From 9a261e2e428d6b24977937337392f8dc6c88fd66 Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Thu, 23 Nov 2023 10:30:04 +0000
Subject: [PATCH] feature: Private Dependencies
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This commit introduces so-called "private dependencies".

High-level Overview
~~~~~~~~~~~~~~~~~~~
Since its inception, Cabal has enforced the restriction that a library
must only link against one version of each package it depends on. This
ensures that all of the dependencies in the build plan work together. In
your application you use different libraries together, so it’s of
paramount importance that they all agree on what `Text` means or what a
`ByteString` is.

However, sometimes it’s desirable to allow multiple versions of the same
library into a build plan. In this case, it’s desirable to allow a
library author to specify a private dependency with the promise that its
existence will not leak from the interface of the library which uses it.

The two main use cases of private dependencies are:

  - Writing benchmarks and testsuites for your library which test new
    versions of your library against old versions.

  - Writing libraries which can communicate with processes built against
    a range of different library versions (such as cabal-install calling
    ./Setup).

A user specifies a private dependency in their cabal file using
`private-build-depends`. The specification starts with the name of the
private dependency scope and then contains a list of normal dependency
specifications which dictates what is included in that private scope:

    private-build-depends: TEXT1 with (text == 1.2.*), TEXT2 with (text == 2.*)

Each private scope is then solved independently of all other scopes. In
this example the TEXT1 scope can choose a version of text in the 1.2.x
range and the TEXT2 scope can choose a version of text in the 2.* range.

Private scopes do not apply transitively, so the dependencies of text
will be solved in the normal top-level scope. If your program contains a
value of type Bool, that comes from the base package, which text depends
on, because the scopes are not applied transitively the same Bool value
can be passed to functions from the TEXT1 scope and TEXT2 scope.

Dependencies introduced privately can be imported into modules in the
project by prefixing the name of the private scope to an exposed module
name.

    import qualified TEXT1.Data.Text as T1
    import qualified TEXT2.Data.Text as T2

Closure of Private Scopes
~~~~~~~~~~~~~~~~~~~~~~~~~

Private dependency scopes can contain multiple packages. Packages in the
same scope are solved together. For example, if two packages are tightly
coupled and you need to use compatible versions with each other, then
you can list them in the same private scope. Such packages will then be
solved together, but independently of other packages.

Private scopes must be closed. A scope is closed if, whenever we have a
dependency chain P1 -> Q -> P2, in which P1 and P2 are both in a given
private scope S, then Q also belongs to the private scope S. The solver
checks this property, but doesn’t implicitly add packages into a private
scope.

Implementation
~~~~~~~~~~~~~~
To implement private dependencies we changed

* Cabal-syntax to introduce the new `private-build-depends: ALIAS (packages, in, private, scope)` syntax.
  See the new type `Dependencies` and changes in `Distribution.Types.Dependency`.

* cabal-install-solver now considers both public and private
  dependencies of a given package (see e.g. `solverPkgLibDeps`), has
  a new constructor `PrivateScope` in `ConstraintScope` for goals in a
  private scope, and there's a new `Qualifier` for packages introduced
  in private scopes (see also [Namespace vs Qualifier refactor] below),
  to solve them separately from packages introduced by `build-depends`.

* cabal-install-solver needs to check that the private-scope closure
  property holds (the closure of the packages in a private scope is in
  the private scope) (see `Distribution.Solver.Modular.PrivateScopeClosure`).

  We check that the closure holds by looking at the reverse dependency
  map while traversing down the tree, at every node:

  For every package in a private scope, traverse up the reverse
  dependency map until a package in the same private scope is found.
  If one exists, and if along the way up any package was not in the same
  private scope as the packages in the two ends, we fail.

* cabal-install understands plans with private dependencies and has a
  new `UserQualifier` to support constrainting packages in private
  scopes using the `--constraint` flag.
  Example: `--constraint=private.pkg-a.TEXT01:text == 1.2.*`

* Cabal the library uses the ghc module-renaming mechanism (also used by
  Backpack) to rename modules from the packages in a private scope to
  prefix them with the private scope alias. It also ensures `cabal
  check` fails if there exist the package has private dependencies, as
  it is currently an experimental feature which we don't necessarily
  want to allow in hackage yet -- e.g. how will haddock render private
  dependencies?

Namespace vs Qualifier refactor
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We also refactored the `Namespace` vs `Qualifier` types in the solver,
clarifying their interaction such that:

* A package goal with an indepedent namespace is fully solved
  indepently from other namespaces, i.e. all the dependency goals
  introduced by a goal in a given namespace are also solved in that
  namespace.

* In contrast, a package goal with a qualifier is shallow-solved
  separately from other goals in the same namespace. The dependency
  goals introduced by it will be solved unqualified (`QualTopLevel`) in
  that namespace.

For example, goal `pkg-a == 0.1` in `DefaultNamespace+QualTopLevel`, and
goal `pkg-a == 0.2` in the same namespace but with `QualAlias A2 ...`
can be solved together and yield a different version of pkg-a for each
of the goals, however, the dependencies of both will be solved together
-- if they both dependend on `base`, we'd have to find a single
solution. If `pkg-a == 0.2` was in an `Independent` namespace, we could
still solve the two goals with two versions of `pkg-a`, but we could
also pick different versions for all the subdependencies of `pkg-a ==
0.2`.

Besides Namespace vs Qualifier being a welcome refactor that facilitates
implementing private dependencies, it also fixes #9466 and helps with #9467.

---

Co-authored-by: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com>
---
 .../src/Test/QuickCheck/Instances/Cabal.hs    |   17 +
 Cabal-described/src/Distribution/Described.hs |   20 +-
 Cabal-syntax/Cabal-syntax.cabal               |    1 +
 .../src/Distribution/FieldGrammar/Parsec.hs   |    2 +
 Cabal-syntax/src/Distribution/ModuleName.hs   |   13 +-
 .../PackageDescription/Configuration.hs       |   51 +-
 .../PackageDescription/FieldGrammar.hs        |   11 +
 .../Distribution/PackageDescription/Parsec.hs |   32 +-
 .../PackageDescription/PrettyPrint.hs         |   28 +-
 .../src/Distribution/Types/BuildInfo.hs       |    3 +
 .../src/Distribution/Types/BuildInfo/Lens.hs  |    9 +-
 .../src/Distribution/Types/ComponentName.hs   |    1 +
 .../src/Distribution/Types/Dependency.hs      |   66 +
 .../src/Distribution/Types/Dependency/Lens.hs |   14 +
 .../src/Distribution/Types/DependencyMap.hs   |   25 +-
 .../Types/GenericPackageDescription.hs        |   20 +-
 .../Types/GenericPackageDescription/Lens.hs   |   18 +-
 .../Distribution/Types/PackageDescription.hs  |   17 +-
 Cabal-tests/tests/NoThunks.hs                 |    3 +
 .../ParserTests/regressions/Octree-0.5.expr   |  128 +-
 .../ParserTests/regressions/anynone.expr      |   14 +-
 .../ParserTests/regressions/big-version.expr  |    6 +-
 .../regressions/common-conditional.expr       |  136 +-
 .../tests/ParserTests/regressions/common.expr |   28 +-
 .../ParserTests/regressions/common2.expr      |  176 ++-
 .../ParserTests/regressions/common3.expr      |   52 +-
 .../tests/ParserTests/regressions/elif.expr   |   20 +-
 .../tests/ParserTests/regressions/elif2.expr  |   46 +-
 .../ParserTests/regressions/encoding-0.8.expr |   22 +-
 .../ParserTests/regressions/generics-sop.expr |  204 +--
 .../ParserTests/regressions/hasktorch.expr    | 1158 +++++++++--------
 .../regressions/hidden-main-lib.expr          |   14 +-
 .../ParserTests/regressions/indentation.expr  |    6 +-
 .../ParserTests/regressions/indentation2.expr |    6 +-
 .../ParserTests/regressions/indentation3.expr |    6 +-
 .../ParserTests/regressions/issue-5055.expr   |   50 +-
 .../ParserTests/regressions/issue-5846.expr   |   78 +-
 .../ParserTests/regressions/issue-6083-a.expr |   92 +-
 .../ParserTests/regressions/issue-6083-b.expr |  102 +-
 .../ParserTests/regressions/issue-6083-c.expr |   38 +-
 .../regressions/issue-6083-pkg-pkg.expr       |   22 +-
 .../ParserTests/regressions/issue-774.expr    |    6 +-
 .../regressions/jaeger-flamegraph.expr        |  178 +--
 .../regressions/leading-comma-2.expr          |   54 +-
 .../regressions/leading-comma.expr            |   54 +-
 .../tests/ParserTests/regressions/libpq1.expr |  112 +-
 .../tests/ParserTests/regressions/libpq2.expr |  112 +-
 .../ParserTests/regressions/mixin-1.expr      |   30 +-
 .../ParserTests/regressions/mixin-2.expr      |   30 +-
 .../ParserTests/regressions/mixin-3.expr      |   30 +-
 .../ParserTests/regressions/monad-param.expr  |   30 +-
 .../regressions/multiple-libs-2.expr          |   28 +-
 .../ParserTests/regressions/noVersion.expr    |   14 +-
 .../regressions/nothing-unicode.expr          |   12 +-
 .../tests/ParserTests/regressions/shake.expr  |  668 +++++-----
 .../tests/ParserTests/regressions/spdx-1.expr |    6 +-
 .../tests/ParserTests/regressions/spdx-2.expr |    6 +-
 .../tests/ParserTests/regressions/spdx-3.expr |    6 +-
 .../regressions/th-lift-instances.expr        |  262 ++--
 .../ParserTests/regressions/version-sets.expr |  106 +-
 .../regressions/wl-pprint-indef.expr          |   56 +-
 .../tests/UnitTests/Distribution/Described.hs |    3 +-
 .../Distribution/Utils/Structured.hs          |    8 +-
 .../src/Data/TreeDiff/Instances/Cabal.hs      |    5 +
 .../Distribution/Backpack/ComponentsGraph.hs  |    2 +-
 Cabal/src/Distribution/Backpack/Configure.hs  |   10 +-
 .../Backpack/ConfiguredComponent.hs           |   33 +-
 .../Distribution/Backpack/LinkedComponent.hs  |   11 +-
 .../src/Distribution/Backpack/ModuleScope.hs  |    4 +-
 .../Backpack/PreExistingComponent.hs          |    7 +-
 Cabal/src/Distribution/Backpack/UnifyM.hs     |   25 +-
 .../Distribution/PackageDescription/Check.hs  |   11 +-
 .../PackageDescription/Check/Conditional.hs   |   30 +-
 Cabal/src/Distribution/Simple/Configure.hs    |   76 +-
 Cabal/src/Distribution/Simple/Errors.hs       |    5 +-
 Cabal/src/Distribution/Simple/GHC/Internal.hs |    2 +-
 Cabal/src/Distribution/Simple/Setup.hs        |    1 +
 Cabal/src/Distribution/Simple/Setup/Config.hs |   32 +-
 .../Distribution/Types/ComponentInclude.hs    |    3 +
 .../Types/ComponentLocalBuildInfo.hs          |    2 +-
 .../src/Distribution/Types/GivenComponent.hs  |    2 +
 .../Distribution/Types/LocalBuildConfig.hs    |    2 +-
 .../src/Distribution/Types/LocalBuildInfo.hs  |    2 +-
 .../cabal-install-solver.cabal                |    1 +
 .../Distribution/Solver/Modular/Builder.hs    |   14 +-
 .../Solver/Modular/ConfiguredConversion.hs    |   61 +-
 .../Solver/Modular/ConflictSet.hs             |    9 +
 .../Distribution/Solver/Modular/Dependency.hs |   51 +-
 .../Distribution/Solver/Modular/Explore.hs    |   15 +-
 .../src/Distribution/Solver/Modular/Index.hs  |    4 +-
 .../Solver/Modular/IndexConversion.hs         |   46 +-
 .../Distribution/Solver/Modular/Linking.hs    |   64 +-
 .../Distribution/Solver/Modular/Message.hs    |    2 +
 .../Distribution/Solver/Modular/Package.hs    |   25 -
 .../Distribution/Solver/Modular/Preference.hs |   15 +-
 .../Solver/Modular/PrivateScopeClosure.hs     |  126 ++
 .../src/Distribution/Solver/Modular/Solver.hs |   10 +-
 .../src/Distribution/Solver/Modular/Tree.hs   |    4 +-
 .../Distribution/Solver/Modular/Validate.hs   |   12 +-
 .../Solver/Types/ComponentDeps.hs             |    2 +-
 .../Solver/Types/InstSolverPackage.hs         |    4 +-
 .../Solver/Types/PackageConstraint.hs         |   34 +-
 .../Distribution/Solver/Types/PackagePath.hs  |   56 +-
 .../Solver/Types/ResolverPackage.hs           |    5 +-
 .../src/Distribution/Solver/Types/SolverId.hs |    5 +-
 .../Solver/Types/SolverPackage.hs             |    3 +-
 .../src/Distribution/Client/CmdOutdated.hs    |    8 +-
 .../src/Distribution/Client/CmdRepl.hs        |    5 +-
 .../src/Distribution/Client/Configure.hs      |    4 +-
 .../src/Distribution/Client/Dependency.hs     |   66 +-
 .../src/Distribution/Client/GenBounds.hs      |   18 +-
 .../src/Distribution/Client/Init/Utils.hs     |    2 +-
 .../src/Distribution/Client/Install.hs        |    4 +-
 .../src/Distribution/Client/InstallPlan.hs    |   21 +-
 .../src/Distribution/Client/InstallSymlink.hs |    2 +-
 cabal-install/src/Distribution/Client/List.hs |    3 +-
 .../src/Distribution/Client/ProjectConfig.hs  |    2 +-
 .../Client/ProjectOrchestration.hs            |    2 +-
 .../Distribution/Client/ProjectPlanOutput.hs  |    6 +-
 .../Distribution/Client/ProjectPlanning.hs    |  128 +-
 .../Client/ProjectPlanning/SetupPolicy.hs     |    2 +-
 .../Client/ProjectPlanning/Types.hs           |   20 +-
 .../src/Distribution/Client/ScriptUtils.hs    |    6 +-
 .../src/Distribution/Client/Setup.hs          |    7 +-
 .../Distribution/Client/SolverInstallPlan.hs  |   48 +-
 .../src/Distribution/Client/Targets.hs        |   38 +-
 .../Client/Types/ConfiguredPackage.hs         |    2 +-
 cabal-install/tests/IntegrationTests2.hs      |    2 +-
 cabal-install/tests/UnitTests.hs              |    3 +-
 .../Distribution/Client/DescribedInstances.hs |    2 +
 .../Distribution/Client/Init/Utils.hs         |   12 +-
 .../Distribution/Solver/Modular/DSL.hs        |   96 +-
 .../Solver/Modular/DSL/TestCaseUtils.hs       |   17 +-
 .../Distribution/Solver/Modular/QuickCheck.hs |   28 +-
 .../Distribution/Solver/Modular/Solver.hs     |  283 +++-
 .../PrivateDeps/cabal-hooks-demo/README.md    |   10 +
 .../cabal-hooks-demo/cabal.project            |    1 +
 .../cabal-hooks-demo/cabal.test.hs            |   20 +
 .../cabal-hooks-demo/hooks-exe/CHANGELOG.md   |    5 +
 .../cabal-hooks-demo/hooks-exe/app/Main.hs    |   35 +
 .../hooks-exe/hooks-exe.cabal                 |   19 +
 .../cabal-hooks-demo/hooks-lib/CHANGELOG.md   |    5 +
 .../hooks-lib/hooks-lib.cabal                 |   20 +
 .../hooks-lib/src/HooksLib.hs                 |  133 ++
 .../cabal-hooks-demo/hooks-lib/src/MyLib.hs   |    4 +
 .../cabal-hooks-demo/main-prog/CHANGELOG.md   |    5 +
 .../cabal-hooks-demo/main-prog/app/Main.hs    |   21 +
 .../main-prog/main-prog.cabal                 |   18 +
 .../repo/lib01-0.1.0.0/CHANGELOG.md           |    5 +
 .../repo/lib01-0.1.0.0/lib01.cabal            |   18 +
 .../repo/lib01-0.1.0.0/src/Lib.hs             |   16 +
 .../repo/lib01-0.2.0.0/CHANGELOG.md           |    5 +
 .../repo/lib01-0.2.0.0/lib01.cabal            |   18 +
 .../repo/lib01-0.2.0.0/src/Lib.hs             |   16 +
 .../closure-property-test/README.md           |   30 +
 .../closure-property-test/cabal.project.1     |    1 +
 .../closure-property-test/cabal.project.2     |    1 +
 .../closure-property-test/cabal.project.3     |    1 +
 .../closure-property-test/cabal.project.4     |    1 +
 .../closure-property-test/cabal.test.hs       |   29 +
 .../libA-0.1.0.0/MyLib.hs                     |    3 +
 .../libA-0.1.0.0/libA.cabal                   |   13 +
 .../libA-0.2.0.0/MyLib.hs                     |    3 +
 .../libA-0.2.0.0/libA.cabal                   |   14 +
 .../libA-0.3.0.0/MyLib.hs                     |    3 +
 .../libA-0.3.0.0/libA.cabal                   |   14 +
 .../libA-0.4.0.0/MyLib.hs                     |    3 +
 .../libA-0.4.0.0/libA.cabal                   |   13 +
 .../repo/libB-0.1.0.0/MyLib.hs                |    3 +
 .../repo/libB-0.1.0.0/libB.cabal              |   12 +
 .../repo/libB-0.2.0.0/MyLib.hs                |    3 +
 .../repo/libB-0.2.0.0/libB.cabal              |   12 +
 .../repo/libB-0.3.0.0/MyLib.hs                |    3 +
 .../repo/libB-0.3.0.0/libB.cabal              |   12 +
 .../repo/libC-0.1.0.0/MyLib.hs                |    3 +
 .../repo/libC-0.1.0.0/libC.cabal              |   11 +
 .../repo/libC-0.2.0.0/MyLib.hs                |    3 +
 .../repo/libC-0.2.0.0/libC.cabal              |   12 +
 .../repo/libD-0.1.0.0/MyLib.hs                |    3 +
 .../repo/libD-0.1.0.0/libD.cabal              |   11 +
 .../PrivateDeps/pd-backpack/README.md         |   15 +
 .../PrivateDeps/pd-backpack/cabal.project     |    1 +
 .../PrivateDeps/pd-backpack/cabal.test.hs     |    9 +
 .../PrivateDeps/pd-backpack/libA/app/Main.hs  |    8 +
 .../PrivateDeps/pd-backpack/libA/libA.cabal   |   22 +
 .../PrivateDeps/pd-backpack/libA/src/A.hs     |    3 +
 .../pd-backpack/libA/src/AHole.hsig           |    3 +
 .../pd-backpack/repo/libB-0.1.0.0/Fill.hs     |    4 +
 .../pd-backpack/repo/libB-0.1.0.0/libB.cabal  |   10 +
 .../pd-backpack/repo/libB-0.1.0.0/tags        |    2 +
 .../pd-backpack/repo/libB-0.2.0.0/Fill.hs     |    4 +
 .../pd-backpack/repo/libB-0.2.0.0/libB.cabal  |   10 +
 .../pd-backpack/repo/libB-0.2.0.0/tags        |    2 +
 .../pd-backpack/repo/libB-0.3.0.0/Fill.hs     |    4 +
 .../pd-backpack/repo/libB-0.3.0.0/libB.cabal  |   10 +
 .../pd-backpack/repo/libB-0.3.0.0/tags        |    2 +
 cabal-testsuite/src/Test/Cabal/Prelude.hs     |    4 +-
 doc/buildinfo-fields-reference.rst            |    7 +
 doc/cabal-package-description-file.rst        |    4 +
 199 files changed, 4536 insertions(+), 2415 deletions(-)
 create mode 100644 Cabal-syntax/src/Distribution/Types/Dependency/Lens.hs
 create mode 100644 cabal-install-solver/src/Distribution/Solver/Modular/PrivateScopeClosure.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/README.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.project
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.test.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/CHANGELOG.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/app/Main.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/hooks-exe.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/CHANGELOG.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/hooks-lib.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/HooksLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/CHANGELOG.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/app/Main.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/main-prog.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/CHANGELOG.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/lib01.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/src/Lib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/CHANGELOG.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/lib01.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/src/Lib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/README.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.1
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.2
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.3
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.4
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.test.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/libA.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/libA.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/libA.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/libA.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/libC.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/libC.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/MyLib.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/libD.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/README.md
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.project
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.test.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/app/Main.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/libA.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/A.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/AHole.hsig
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/Fill.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/tags
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/Fill.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/tags
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/Fill.hs
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/libB.cabal
 create mode 100644 cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/tags

diff --git a/Cabal-QuickCheck/src/Test/QuickCheck/Instances/Cabal.hs b/Cabal-QuickCheck/src/Test/QuickCheck/Instances/Cabal.hs
index e5b5077d414..91fd47863cf 100644
--- a/Cabal-QuickCheck/src/Test/QuickCheck/Instances/Cabal.hs
+++ b/Cabal-QuickCheck/src/Test/QuickCheck/Instances/Cabal.hs
@@ -208,6 +208,23 @@ instance Arbitrary Dependency where
         | (pn', vr', lb') <- shrink (pn, vr, lb)
         ]
 
+-------------------------------------------------------------------------------
+-- Private Dependency
+-------------------------------------------------------------------------------
+
+instance Arbitrary PrivateAlias where
+  arbitrary = PrivateAlias <$> arbitrary
+  shrink (PrivateAlias al) = PrivateAlias <$> shrink al
+instance Arbitrary PrivateDependency where
+    arbitrary = PrivateDependency
+        <$> arbitrary
+        <*> arbitrary
+
+    shrink (PrivateDependency al dps) =
+        [ PrivateDependency al' dps'
+        | (al', dps') <- shrink (al, dps)
+        ]
+
 -------------------------------------------------------------------------------
 -- PackageVersionConstraint
 -------------------------------------------------------------------------------
diff --git a/Cabal-described/src/Distribution/Described.hs b/Cabal-described/src/Distribution/Described.hs
index 8c1c501cf95..8f48aa25a93 100644
--- a/Cabal-described/src/Distribution/Described.hs
+++ b/Cabal-described/src/Distribution/Described.hs
@@ -76,7 +76,7 @@ import Distribution.Types.AbiDependency            (AbiDependency)
 import Distribution.Types.AbiHash                  (AbiHash)
 import Distribution.Types.BenchmarkType            (BenchmarkType)
 import Distribution.Types.BuildType                (BuildType)
-import Distribution.Types.Dependency               (Dependency)
+import Distribution.Types.Dependency               (Dependency, PrivateAlias(..), PrivateDependency)
 import Distribution.Types.ExecutableScope          (ExecutableScope)
 import Distribution.Types.ExeDependency            (ExeDependency)
 import Distribution.Types.ExposedModule            (ExposedModule)
@@ -370,7 +370,7 @@ instance Described CompilerId where
         <> describe (Proxy :: Proxy Version)
 
 instance Described Dependency where
-    describe _ = REAppend
+  describe _ = REAppend
         [ RENamed "pkg-name" (describe (Proxy :: Proxy PackageName))
         , REOpt $
                reChar ':'
@@ -391,6 +391,19 @@ instance Described Dependency where
       where
         vr = RENamed "version-range" (describe (Proxy :: Proxy VersionRange))
 
+instance Described PrivateDependency where
+    describe _ = REAppend
+        [ RENamed "alias" (describe (Proxy :: Proxy PrivateAlias))
+        , RESpaces1
+        , "with"
+        , RESpaces1
+        , reChar '('
+        , RESpaces
+        , REMunch reSpacedComma (describe (Proxy :: Proxy Dependency))
+        , RESpaces
+        , reChar ')'
+        ]
+
 instance Described ExecutableScope where
     describe _ = REUnion ["public","private"]
 
@@ -446,6 +459,9 @@ instance Described ModuleName where
     describe _ = REMunch1 (reChar '.') component where
         component = RECharSet csUpper <> REMunch reEps (REUnion [RECharSet csAlphaNum, RECharSet (fromString "_'")])
 
+instance Described PrivateAlias where
+  describe _ = describe (Proxy :: Proxy ModuleName)
+
 instance Described ModuleReexport where
     describe _ = RETodo
 
diff --git a/Cabal-syntax/Cabal-syntax.cabal b/Cabal-syntax/Cabal-syntax.cabal
index 46c4ce4fc22..6b4a6c887ba 100644
--- a/Cabal-syntax/Cabal-syntax.cabal
+++ b/Cabal-syntax/Cabal-syntax.cabal
@@ -138,6 +138,7 @@ library
     Distribution.Types.Condition
     Distribution.Types.ConfVar
     Distribution.Types.Dependency
+    Distribution.Types.Dependency.Lens
     Distribution.Types.DependencyMap
     Distribution.Types.ExeDependency
     Distribution.Types.Executable
diff --git a/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs b/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
index 4721aa4ad08..bce432e4e4e 100644
--- a/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
+++ b/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
@@ -1,6 +1,8 @@
 {-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE InstanceSigs #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE PartialTypeSignatures #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 -- | This module provides a 'FieldGrammarParser', one way to parse
diff --git a/Cabal-syntax/src/Distribution/ModuleName.hs b/Cabal-syntax/src/Distribution/ModuleName.hs
index 90082d29f06..bdaf4e0d10e 100644
--- a/Cabal-syntax/src/Distribution/ModuleName.hs
+++ b/Cabal-syntax/src/Distribution/ModuleName.hs
@@ -99,12 +99,6 @@ validModuleComponent (c : cs) = isUpper c && all validModuleChar cs
 instance IsString ModuleName where
   fromString = ModuleName . toShortText
 
--- | Construct a 'ModuleName' from valid module components, i.e. parts
--- separated by dots.
-fromComponents :: [String] -> ModuleName
-fromComponents comps = fromString (intercalate "." comps)
-{-# DEPRECATED fromComponents "Exists for cabal-install only" #-}
-
 -- | The module name @Main@.
 main :: ModuleName
 main = ModuleName (fromString "Main")
@@ -119,6 +113,13 @@ components mn = split (unModuleName mn)
       (chunk, []) -> chunk : []
       (chunk, _ : rest) -> chunk : split rest
 
+-- | Construct a 'ModuleName' from valid module components, i.e. parts
+-- separated by dots.
+--
+-- Inverse of 'components', i.e. @fromComponents (components x) = x@
+fromComponents :: [String] -> ModuleName
+fromComponents comps = fromString (intercalate "." comps)
+
 -- | Convert a module name to a file path, but without any file extension.
 -- For example:
 --
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs b/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
index e811c361221..3c41da30b6d 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/Configuration.hs
@@ -31,7 +31,6 @@ module Distribution.PackageDescription.Configuration
   , mapTreeConstrs
   , transformAllBuildInfos
   , transformAllBuildDepends
-  , transformAllBuildDependsN
   , simplifyWithSysParams
   ) where
 
@@ -63,6 +62,7 @@ import Distribution.Version
 
 import qualified Data.Map.Lazy as Map
 import Data.Tree (Tree (Node))
+import qualified Distribution.Types.Dependency.Lens as L
 
 ------------------------------------------------------------------------------
 
@@ -189,10 +189,10 @@ resolveWithFlags
   -- ^ Compiler information
   -> [PackageVersionConstraint]
   -- ^ Additional constraints
-  -> [CondTree ConfVar [Dependency] PDTagged]
-  -> ([Dependency] -> DepTestRslt [Dependency])
+  -> [CondTree ConfVar Dependencies PDTagged]
+  -> (Dependencies -> DepTestRslt Dependencies)
   -- ^ Dependency test function.
-  -> Either [Dependency] (TargetSet PDTagged, FlagAssignment)
+  -> Either Dependencies (TargetSet PDTagged, FlagAssignment)
   -- ^ Either the missing dependencies (error case), or a pair of
   -- (set of build targets with dependencies, chosen flag assignments)
 resolveWithFlags dom enabled os arch impl constrs trees checkDeps =
@@ -324,7 +324,7 @@ extractConditions f gpkg =
     ]
 
 -- | A map of package constraints that combines version ranges using 'unionVersionRanges'.
-newtype DepMapUnion = DepMapUnion {unDepMapUnion :: Map PackageName (VersionRange, NonEmptySet LibraryName)}
+newtype DepMapUnion = DepMapUnion {unDepMapUnion :: Map (PackageName, IsPrivate) (VersionRange, NonEmptySet LibraryName)}
 
 instance Semigroup DepMapUnion where
   DepMapUnion x <> DepMapUnion y =
@@ -337,12 +337,22 @@ unionVersionRanges'
   -> (VersionRange, NonEmptySet LibraryName)
 unionVersionRanges' (vr, cs) (vr', cs') = (unionVersionRanges vr vr', cs <> cs')
 
-toDepMapUnion :: [Dependency] -> DepMapUnion
+toDepMapUnion :: Dependencies -> DepMapUnion
 toDepMapUnion ds =
-  DepMapUnion $ Map.fromListWith unionVersionRanges' [(p, (vr, cs)) | Dependency p vr cs <- ds]
+  DepMapUnion $
+    Map.fromListWith
+      unionVersionRanges'
+      ( [((p, Public), (vr, cs)) | Dependency p vr cs <- publicDependencies ds]
+          ++ [((p, Private (private_alias d)), (vr, cs)) | d <- privateDependencies ds, Dependency p vr cs <- private_depends d]
+      )
 
-fromDepMapUnion :: DepMapUnion -> [Dependency]
-fromDepMapUnion m = [Dependency p vr cs | (p, (vr, cs)) <- Map.toList (unDepMapUnion m)]
+fromDepMapUnion :: DepMapUnion -> Dependencies
+fromDepMapUnion m =
+  Dependencies
+    [Dependency p vr cs | ((p, Public), (vr, cs)) <- Map.toList (unDepMapUnion m)]
+    [PrivateDependency alias deps | (alias, deps) <- Map.toList priv_deps]
+  where
+    priv_deps = Map.fromListWith (++) [(sn, [Dependency p vr cs]) | ((p, Private sn), (vr, cs)) <- Map.toList (unDepMapUnion m)]
 
 freeVars :: CondTree ConfVar c a -> [FlagName]
 freeVars t = [f | PackageFlag f <- freeVars' t]
@@ -400,8 +410,9 @@ flattenTaggedTargets (TargetSet targets) = foldr untag (Nothing, []) targets
         | otherwise -> (mb_lib, (n, redoBD c) : comps)
       (PDNull, x) -> x -- actually this should not happen, but let's be liberal
       where
+        deps = fromDepMap depMap
         redoBD :: L.HasBuildInfo a => a -> a
-        redoBD = set L.targetBuildDepends $ fromDepMap depMap
+        redoBD = set L.targetPrivateBuildDepends (privateDependencies deps) . set L.targetBuildDepends (publicDependencies deps)
 
 ------------------------------------------------------------------------------
 -- Convert GenericPackageDescription to PackageDescription
@@ -453,7 +464,7 @@ finalizePD
   :: FlagAssignment
   -- ^ Explicitly specified flag assignments
   -> ComponentRequestedSpec
-  -> (Dependency -> Bool)
+  -> (Maybe PrivateAlias -> Dependency -> Bool)
   -- ^ Is a given dependency satisfiable from the set of
   -- available packages?  If this is unknown then use
   -- True.
@@ -465,7 +476,7 @@ finalizePD
   -- ^ Additional constraints
   -> GenericPackageDescription
   -> Either
-      [Dependency]
+      Dependencies
       (PackageDescription, FlagAssignment)
   -- ^ Either missing dependencies or the resolved package
   -- description along with the flag assignments chosen.
@@ -526,8 +537,11 @@ finalizePD
           | otherwise -> [b, not b]
       -- flagDefaults = map (\(n,x:_) -> (n,x)) flagChoices
       check ds =
-        let missingDeps = filter (not . satisfyDep) ds
-         in if null missingDeps
+        let missingDeps =
+              Dependencies
+                (filter (not . satisfyDep Nothing) (publicDependencies ds))
+                (mapMaybe (\(PrivateDependency priv pds) -> case filter (not . satisfyDep (Just priv)) pds of [] -> Nothing; pds' -> Just (PrivateDependency priv pds')) (privateDependencies ds))
+         in if null (publicDependencies missingDeps) && null (privateDependencies missingDeps)
               then DepOk
               else MissingDeps missingDeps
 
@@ -652,15 +666,17 @@ transformAllBuildDepends
   -> GenericPackageDescription
   -> GenericPackageDescription
 transformAllBuildDepends f =
-  over (L.traverseBuildInfos . L.targetBuildDepends . traverse) f
+  over (L.traverseBuildInfos . L.targetPrivateBuildDepends . traverse . L.private_depends . traverse) f
+    . over (L.traverseBuildInfos . L.targetBuildDepends . traverse) f
     . over (L.packageDescription . L.setupBuildInfo . traverse . L.setupDepends . traverse) f
     -- cannot be point-free as normal because of higher rank
-    . over (\f' -> L.allCondTrees $ traverseCondTreeC f') (map f)
+    . over (\f' -> L.allCondTrees $ traverseCondTreeC f') (mapDependencies f)
 
+{-
 -- | Walk a 'GenericPackageDescription' and apply @f@ to all nested
 -- @build-depends@ fields.
 transformAllBuildDependsN
-  :: ([Dependency] -> [Dependency])
+  :: (Dependencies -> Dependencies)
   -> GenericPackageDescription
   -> GenericPackageDescription
 transformAllBuildDependsN f =
@@ -668,3 +684,4 @@ transformAllBuildDependsN f =
     . over (L.packageDescription . L.setupBuildInfo . traverse . L.setupDepends) f
     -- cannot be point-free as normal because of higher rank
     . over (\f' -> L.allCondTrees $ traverseCondTreeC f') f
+    -}
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs b/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
index db6b7f7607b..e98cc5ed1a6 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
@@ -171,6 +171,7 @@ libraryFieldGrammar
      , c (List CommaFSep (Identity LegacyExeDependency) LegacyExeDependency)
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
      , c (List CommaVCat (Identity Dependency) Dependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List CommaVCat (Identity ModuleReexport) ModuleReexport)
      , c (List FSep (MQuoted Extension) Extension)
@@ -220,6 +221,7 @@ foreignLibFieldGrammar
      , c (List CommaFSep (Identity ExeDependency) ExeDependency)
      , c (List CommaFSep (Identity LegacyExeDependency) LegacyExeDependency)
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Dependency) Dependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List FSep (Identity ForeignLibOption) ForeignLibOption)
@@ -260,6 +262,7 @@ executableFieldGrammar
      , c (List CommaFSep (Identity LegacyExeDependency) LegacyExeDependency)
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
      , c (List CommaVCat (Identity Dependency) Dependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List FSep (MQuoted Extension) Extension)
      , c (List FSep (MQuoted Language) Language)
@@ -336,6 +339,7 @@ testSuiteFieldGrammar
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
      , c (List CommaFSep Token String)
      , c (List CommaVCat (Identity Dependency) Dependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List FSep (MQuoted Extension) Extension)
      , c (List FSep (MQuoted Language) Language)
@@ -348,6 +352,7 @@ testSuiteFieldGrammar
      , forall from to. c (RelativePathNT from to)
      , c (List VCat Token String)
      , c (MQuoted Language)
+     , c PrivateAlias
      )
   => g TestSuiteStanza TestSuiteStanza
 testSuiteFieldGrammar =
@@ -480,6 +485,7 @@ benchmarkFieldGrammar
      , c (List CommaFSep (Identity LegacyExeDependency) LegacyExeDependency)
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
      , c (List CommaVCat (Identity Dependency) Dependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List FSep (MQuoted Extension) Extension)
      , c (List FSep (MQuoted Language) Language)
@@ -582,6 +588,7 @@ buildInfoFieldGrammar
      , c (List CommaFSep (Identity LegacyExeDependency) LegacyExeDependency)
      , c (List CommaFSep (Identity PkgconfigDependency) PkgconfigDependency)
      , c (List CommaVCat (Identity Dependency) Dependency)
+     , c (List CommaVCat (Identity PrivateDependency) PrivateDependency)
      , c (List CommaVCat (Identity Mixin) Mixin)
      , c (List FSep (MQuoted Extension) Extension)
      , c (List FSep (MQuoted Language) Language)
@@ -676,6 +683,7 @@ buildInfoFieldGrammar =
     <*> pure mempty -- static-options ???
     <*> prefixedFields "x-" L.customFieldsBI
     <*> monoidalFieldAla "build-depends" formatDependencyList L.targetBuildDepends
+    <*> monoidalFieldAla "private-build-depends" formatPrivateDependencyList L.targetPrivateBuildDepends -- (map (\(PrivateDependency a ds) -> (a, formatDependencyList ds))) (map (\(alias, ds) -> PrivateDependency alias (unpack' formatDependencyList ds))) L.targetPrivateBuildDepends
     <*> monoidalFieldAla "mixins" formatMixinList L.mixins
       ^^^ availableSince CabalSpecV2_0 []
 {-# SPECIALIZE buildInfoFieldGrammar :: ParsecFieldGrammar' BuildInfo #-}
@@ -800,6 +808,9 @@ setupBInfoFieldGrammar def =
 formatDependencyList :: [Dependency] -> List CommaVCat (Identity Dependency) Dependency
 formatDependencyList = alaList CommaVCat
 
+formatPrivateDependencyList :: [PrivateDependency] -> List CommaVCat (Identity PrivateDependency) PrivateDependency
+formatPrivateDependencyList = alaList CommaVCat
+
 formatMixinList :: [Mixin] -> List CommaVCat (Identity Mixin) Mixin
 formatMixinList = alaList CommaVCat
 
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs b/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
index cd299b87675..0cbb32df6c5 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -64,6 +65,7 @@ import qualified Data.Set as Set
 import qualified Distribution.Compat.Newtype as Newtype
 import qualified Distribution.Compat.NonEmptySet as NES
 import qualified Distribution.Types.BuildInfo.Lens as L
+import qualified Distribution.Types.Dependency.Lens as L
 import qualified Distribution.Types.Executable.Lens as L
 import qualified Distribution.Types.ForeignLib.Lens as L
 import qualified Distribution.Types.GenericPackageDescription.Lens as L
@@ -189,6 +191,7 @@ parseGenericPackageDescription' scannedVer lexWarnings utf8WarnPos fs = do
 
   -- Package description
   pd <- parseFieldGrammar specVer fields packageDescriptionFieldGrammar
+  !_ <- pd `deepseq` return pd
 
   -- Check that scanned and parsed versions match.
   unless (specVer == specVersion pd) $
@@ -264,7 +267,7 @@ goSections specVer = traverse_ process
       -> Map String CondTreeBuildInfo
       -- \^ common stanzas
       -> [Field Position]
-      -> ParseResult (CondTree ConfVar [Dependency] a)
+      -> ParseResult (CondTree ConfVar Dependencies a)
     parseCondTree' = parseCondTreeWithCommonStanzas specVer
 
     parseSection :: Name Position -> [SectionArg Position] -> [Field Position] -> SectionParser ()
@@ -480,10 +483,10 @@ parseCondTree
   -- ^ common stanzas
   -> (BuildInfo -> a)
   -- ^ constructor from buildInfo
-  -> (a -> [Dependency])
+  -> (a -> Dependencies)
   -- ^ condition extractor
   -> [Field Position]
-  -> ParseResult (CondTree ConfVar [Dependency] a)
+  -> ParseResult (CondTree ConfVar Dependencies a)
 parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
   where
     go fields0 = do
@@ -497,7 +500,7 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
       branches <- concat <$> traverse parseIfs ss
       return $ endo $ CondNode x (cond x) branches
 
-    parseIfs :: [Section Position] -> ParseResult [CondBranch ConfVar [Dependency] a]
+    parseIfs :: [Section Position] -> ParseResult [CondBranch ConfVar Dependencies a]
     parseIfs [] = return []
     parseIfs (MkSection (Name _ name) test fields : sections) | name == "if" = do
       test' <- parseConditionConfVar test
@@ -510,7 +513,7 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
 
     parseElseIfs
       :: [Section Position]
-      -> ParseResult (Maybe (CondTree ConfVar [Dependency] a), [CondBranch ConfVar [Dependency] a])
+      -> ParseResult (Maybe (CondTree ConfVar Dependencies a), [CondBranch ConfVar Dependencies a])
     parseElseIfs [] = return (Nothing, [])
     parseElseIfs (MkSection (Name pos name) args fields : sections) | name == "else" = do
       unless (null args) $
@@ -589,7 +592,7 @@ with new AST, this all need to be rewritten.
 -- The approach is simple, and have good properties:
 --
 -- * Common stanzas are parsed exactly once, even if not-used. Thus we report errors in them.
-type CondTreeBuildInfo = CondTree ConfVar [Dependency] BuildInfo
+type CondTreeBuildInfo = CondTree ConfVar Dependencies BuildInfo
 
 -- | Create @a@ from 'BuildInfo'.
 -- This class is used to implement common stanza parsing.
@@ -631,10 +634,10 @@ parseCondTreeWithCommonStanzas
   -> Map String CondTreeBuildInfo
   -- ^ common stanzas
   -> [Field Position]
-  -> ParseResult (CondTree ConfVar [Dependency] a)
+  -> ParseResult (CondTree ConfVar Dependencies a)
 parseCondTreeWithCommonStanzas v grammar fromBuildInfo commonStanzas fields = do
   (fields', endo) <- processImports v fromBuildInfo commonStanzas fields
-  x <- parseCondTree v hasElif grammar commonStanzas fromBuildInfo (view L.targetBuildDepends) fields'
+  x <- parseCondTree v hasElif grammar commonStanzas fromBuildInfo (\bi -> Dependencies (view L.targetBuildDepends bi) (view L.targetPrivateBuildDepends bi)) fields'
   return (endo x)
   where
     hasElif = specHasElif v
@@ -648,7 +651,7 @@ processImports
   -> Map String CondTreeBuildInfo
   -- ^ common stanzas
   -> [Field Position]
-  -> ParseResult ([Field Position], CondTree ConfVar [Dependency] a -> CondTree ConfVar [Dependency] a)
+  -> ParseResult ([Field Position], CondTree ConfVar Dependencies a -> CondTree ConfVar Dependencies a)
 processImports v fromBuildInfo commonStanzas = go []
   where
     hasCommonStanzas = specHasCommonStanzas v
@@ -691,11 +694,11 @@ warnImport _ f = pure (Just f)
 mergeCommonStanza
   :: L.HasBuildInfo a
   => (BuildInfo -> a)
-  -> CondTree ConfVar [Dependency] BuildInfo
-  -> CondTree ConfVar [Dependency] a
-  -> CondTree ConfVar [Dependency] a
+  -> CondTree ConfVar Dependencies BuildInfo
+  -> CondTree ConfVar Dependencies a
+  -> CondTree ConfVar Dependencies a
 mergeCommonStanza fromBuildInfo (CondNode bi _ bis) (CondNode x _ cs) =
-  CondNode x' (x' ^. L.targetBuildDepends) cs'
+  CondNode x' (Dependencies (view L.targetBuildDepends x') (view L.targetPrivateBuildDepends x')) cs'
   where
     -- new value is old value with buildInfo field _prepended_.
     x' = x & L.buildInfo %~ (bi <>)
@@ -810,7 +813,8 @@ postProcessInternalDeps specVer gpd
   where
     transformBI :: BuildInfo -> BuildInfo
     transformBI =
-      over L.targetBuildDepends (concatMap transformD)
+      over (L.targetPrivateBuildDepends . traverse . L.private_depends) (concatMap transformD)
+        . over L.targetBuildDepends (concatMap transformD)
         . over L.mixins (map transformM)
 
     transformSBI :: SetupBuildInfo -> SetupBuildInfo
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/PrettyPrint.hs b/Cabal-syntax/src/Distribution/PackageDescription/PrettyPrint.hs
index b03b1b99ada..425b273aeb2 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/PrettyPrint.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/PrettyPrint.hs
@@ -61,6 +61,7 @@ import Text.PrettyPrint (Doc, char, hsep, parens, text)
 
 import qualified Data.ByteString.Lazy.Char8 as BS.Char8
 import qualified Distribution.Compat.NonEmptySet as NES
+import qualified Distribution.Types.Dependency.Lens as L
 
 -- | Writes a .cabal file from a generic package description
 writeGenericPackageDescription :: FilePath -> GenericPackageDescription -> IO ()
@@ -121,7 +122,7 @@ ppFlag v flag@(MkPackageFlag name _ _ _) =
   PrettySection () "flag" [ppFlagName name] $
     prettyFieldGrammar v (flagFieldGrammar name) flag
 
-ppCondTree2 :: CabalSpecVersion -> PrettyFieldGrammar' s -> CondTree ConfVar [Dependency] s -> [PrettyField ()]
+ppCondTree2 :: CabalSpecVersion -> PrettyFieldGrammar' s -> CondTree ConfVar Dependencies s -> [PrettyField ()]
 ppCondTree2 v grammar = go
   where
     -- TODO: recognise elif opportunities
@@ -140,42 +141,42 @@ ppCondTree2 v grammar = go
       , PrettySection () "else" [] (go elseTree)
       ]
 
-ppCondLibrary :: CabalSpecVersion -> Maybe (CondTree ConfVar [Dependency] Library) -> [PrettyField ()]
+ppCondLibrary :: CabalSpecVersion -> Maybe (CondTree ConfVar Dependencies Library) -> [PrettyField ()]
 ppCondLibrary _ Nothing = mempty
 ppCondLibrary v (Just condTree) =
   pure $
     PrettySection () "library" [] $
       ppCondTree2 v (libraryFieldGrammar LMainLibName) condTree
 
-ppCondSubLibraries :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar [Dependency] Library)] -> [PrettyField ()]
+ppCondSubLibraries :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar Dependencies Library)] -> [PrettyField ()]
 ppCondSubLibraries v libs =
   [ PrettySection () "library" [pretty n] $
     ppCondTree2 v (libraryFieldGrammar $ LSubLibName n) condTree
   | (n, condTree) <- libs
   ]
 
-ppCondForeignLibs :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar [Dependency] ForeignLib)] -> [PrettyField ()]
+ppCondForeignLibs :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar Dependencies ForeignLib)] -> [PrettyField ()]
 ppCondForeignLibs v flibs =
   [ PrettySection () "foreign-library" [pretty n] $
     ppCondTree2 v (foreignLibFieldGrammar n) condTree
   | (n, condTree) <- flibs
   ]
 
-ppCondExecutables :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar [Dependency] Executable)] -> [PrettyField ()]
+ppCondExecutables :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar Dependencies Executable)] -> [PrettyField ()]
 ppCondExecutables v exes =
   [ PrettySection () "executable" [pretty n] $
     ppCondTree2 v (executableFieldGrammar n) condTree
   | (n, condTree) <- exes
   ]
 
-ppCondTestSuites :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar [Dependency] TestSuite)] -> [PrettyField ()]
+ppCondTestSuites :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar Dependencies TestSuite)] -> [PrettyField ()]
 ppCondTestSuites v suites =
   [ PrettySection () "test-suite" [pretty n] $
     ppCondTree2 v testSuiteFieldGrammar (fmap FG.unvalidateTestSuite condTree)
   | (n, condTree) <- suites
   ]
 
-ppCondBenchmarks :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar [Dependency] Benchmark)] -> [PrettyField ()]
+ppCondBenchmarks :: CabalSpecVersion -> [(UnqualComponentName, CondTree ConfVar Dependencies Benchmark)] -> [PrettyField ()]
 ppCondBenchmarks v suites =
   [ PrettySection () "benchmark" [pretty n] $
     ppCondTree2 v benchmarkFieldGrammar (fmap FG.unvalidateBenchmark condTree)
@@ -239,16 +240,16 @@ pdToGpd pd =
     , condBenchmarks = mkCondTree' benchmarkName <$> benchmarks pd
     }
   where
-    -- We set CondTree's [Dependency] to an empty list, as it
+    -- We set CondTree's Dependencies to an empty list, as it
     -- is not pretty printed anyway.
-    mkCondTree x = CondNode x [] []
-    mkCondTreeL l = (fromMaybe (mkUnqualComponentName "") (libraryNameString (libName l)), CondNode l [] [])
+    mkCondTree x = CondNode x mempty mempty
+    mkCondTreeL l = (fromMaybe (mkUnqualComponentName "") (libraryNameString (libName l)), CondNode l mempty mempty)
 
     mkCondTree'
       :: (a -> UnqualComponentName)
       -> a
-      -> (UnqualComponentName, CondTree ConfVar [Dependency] a)
-    mkCondTree' f x = (f x, CondNode x [] [])
+      -> (UnqualComponentName, CondTree ConfVar Dependencies a)
+    mkCondTree' f x = (f x, CondNode x mempty [])
 
 -------------------------------------------------------------------------------
 -- Internal libs
@@ -263,7 +264,8 @@ preProcessInternalDeps specVer gpd
   where
     transformBI :: BuildInfo -> BuildInfo
     transformBI =
-      over L.targetBuildDepends (concatMap transformD)
+      over (L.targetPrivateBuildDepends . traverse . L.private_depends) (concatMap transformD)
+        . over L.targetBuildDepends (concatMap transformD)
         . over L.mixins (map transformM)
 
     transformSBI :: SetupBuildInfo -> SetupBuildInfo
diff --git a/Cabal-syntax/src/Distribution/Types/BuildInfo.hs b/Cabal-syntax/src/Distribution/Types/BuildInfo.hs
index da1f8aea88f..5fd8e737b9f 100644
--- a/Cabal-syntax/src/Distribution/Types/BuildInfo.hs
+++ b/Cabal-syntax/src/Distribution/Types/BuildInfo.hs
@@ -140,6 +140,7 @@ data BuildInfo = BuildInfo
   --  simple assoc-list.
   , targetBuildDepends :: [Dependency]
   -- ^ Dependencies specific to a library or executable target
+  , targetPrivateBuildDepends :: [PrivateDependency]
   , mixins :: [Mixin]
   }
   deriving (Generic, Show, Read, Eq, Ord, Typeable, Data)
@@ -196,6 +197,7 @@ instance Monoid BuildInfo where
       , staticOptions = mempty
       , customFieldsBI = []
       , targetBuildDepends = []
+      , targetPrivateBuildDepends = []
       , mixins = []
       }
   mappend = (<>)
@@ -248,6 +250,7 @@ instance Semigroup BuildInfo where
       , staticOptions = combine staticOptions
       , customFieldsBI = combine customFieldsBI
       , targetBuildDepends = combineNub targetBuildDepends
+      , targetPrivateBuildDepends = combineNub targetPrivateBuildDepends
       , mixins = combine mixins
       }
     where
diff --git a/Cabal-syntax/src/Distribution/Types/BuildInfo/Lens.hs b/Cabal-syntax/src/Distribution/Types/BuildInfo/Lens.hs
index 19453a671b9..84b49ad7bb1 100644
--- a/Cabal-syntax/src/Distribution/Types/BuildInfo/Lens.hs
+++ b/Cabal-syntax/src/Distribution/Types/BuildInfo/Lens.hs
@@ -13,7 +13,7 @@ import Prelude ()
 import Distribution.Compiler (PerCompilerFlavor)
 import Distribution.ModuleName (ModuleName)
 import Distribution.Types.BuildInfo (BuildInfo)
-import Distribution.Types.Dependency (Dependency)
+import Distribution.Types.Dependency (Dependency, PrivateDependency)
 import Distribution.Types.ExeDependency (ExeDependency)
 import Distribution.Types.LegacyExeDependency (LegacyExeDependency)
 import Distribution.Types.Mixin (Mixin)
@@ -207,6 +207,10 @@ class HasBuildInfo a where
   targetBuildDepends = buildInfo . targetBuildDepends
   {-# INLINE targetBuildDepends #-}
 
+  targetPrivateBuildDepends :: Lens' a [PrivateDependency]
+  targetPrivateBuildDepends = buildInfo . targetPrivateBuildDepends
+  {-# INLINE targetPrivateBuildDepends #-}
+
   mixins :: Lens' a [Mixin]
   mixins = buildInfo . mixins
   {-# INLINE mixins #-}
@@ -350,6 +354,9 @@ instance HasBuildInfo BuildInfo where
   targetBuildDepends f s = fmap (\x -> s{T.targetBuildDepends = x}) (f (T.targetBuildDepends s))
   {-# INLINE targetBuildDepends #-}
 
+  targetPrivateBuildDepends f s = fmap (\x -> s{T.targetPrivateBuildDepends = x}) (f (T.targetPrivateBuildDepends s))
+  {-# INLINE targetPrivateBuildDepends #-}
+
   mixins f s = fmap (\x -> s{T.mixins = x}) (f (T.mixins s))
   {-# INLINE mixins #-}
 
diff --git a/Cabal-syntax/src/Distribution/Types/ComponentName.hs b/Cabal-syntax/src/Distribution/Types/ComponentName.hs
index 01ed6f7655f..2b791bb50cc 100644
--- a/Cabal-syntax/src/Distribution/Types/ComponentName.hs
+++ b/Cabal-syntax/src/Distribution/Types/ComponentName.hs
@@ -8,6 +8,7 @@ module Distribution.Types.ComponentName
   , componentNameRaw
   , componentNameStanza
   , componentNameString
+  , NotLibComponentName (..)
   ) where
 
 import Distribution.Compat.Prelude
diff --git a/Cabal-syntax/src/Distribution/Types/Dependency.hs b/Cabal-syntax/src/Distribution/Types/Dependency.hs
index 10d0506b57e..a50c863d6bd 100644
--- a/Cabal-syntax/src/Distribution/Types/Dependency.hs
+++ b/Cabal-syntax/src/Distribution/Types/Dependency.hs
@@ -1,5 +1,7 @@
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 
 module Distribution.Types.Dependency
   ( Dependency (..)
@@ -9,6 +11,11 @@ module Distribution.Types.Dependency
   , depLibraries
   , simplifyDependency
   , mainLibSet
+  , PrivateDependency (..)
+  , PrivateAlias (..)
+  , Dependencies (..)
+  , IsPrivate (..)
+  , mapDependencies
   ) where
 
 import Distribution.Compat.Prelude
@@ -26,9 +33,55 @@ import Distribution.Types.LibraryName
 import Distribution.Types.PackageName
 import Distribution.Types.UnqualComponentName
 
+import qualified Distribution.Compat.CharParsing as P
 import qualified Distribution.Compat.NonEmptySet as NES
+import Distribution.ModuleName
 import qualified Text.PrettyPrint as PP
 
+data IsPrivate = Private PrivateAlias | Public deriving (Show, Ord, Read, Eq)
+
+data Dependencies = Dependencies {publicDependencies :: [Dependency], privateDependencies :: [PrivateDependency]} deriving (Eq, Show, Generic, Data)
+
+newtype PrivateAlias = PrivateAlias ModuleName deriving (Show, Eq, Generic, Data, Read, Ord)
+
+instance Pretty PrivateAlias where
+  pretty (PrivateAlias p) = pretty p
+
+instance Parsec PrivateAlias where
+  parsec = PrivateAlias <$> parsec
+
+-- | Construct a 'PrivateAlias' from a valid module name 'String'.
+--
+-- This is just a convenience function intended for valid module strings. It is
+-- an error if it is used with a string that is not a valid module name. If you
+-- are parsing user input then use 'Distribution.Text.simpleParse' instead.
+instance IsString PrivateAlias where
+  fromString = PrivateAlias . fromString
+
+data PrivateDependency = PrivateDependency {private_alias :: PrivateAlias, private_depends :: [Dependency]} deriving (Eq, Show, Generic, Data, Read, Ord)
+
+instance Parsec PrivateDependency where
+  parsec = do
+    alias <- parsec
+    P.spaces
+    _ <- P.string "with"
+    P.spaces
+    let parensLax p = P.between (P.char '(' >> P.spaces) (P.char ')' >> P.spaces) p
+    deps <- parensLax (parsecCommaList parsec)
+    return (PrivateDependency alias deps)
+
+instance Pretty PrivateDependency where
+  pretty (PrivateDependency alias deps) = PP.hsep [pretty alias, PP.text "with", PP.parens (PP.hsep (PP.punctuate PP.comma (map pretty deps)))]
+
+instance Semigroup Dependencies where
+  (Dependencies p1 pr1) <> (Dependencies p2 pr2) = Dependencies (p1 <> p2) (pr1 <> pr2)
+
+instance Monoid Dependencies where
+  mempty = Dependencies mempty mempty
+
+mapDependencies :: (Dependency -> Dependency) -> Dependencies -> Dependencies
+mapDependencies f (Dependencies pub priv) = Dependencies (map f pub) (map (\d -> d{private_depends = map f (private_depends d)}) priv)
+
 -- | Describes a dependency on a source package (API)
 --
 -- /Invariant:/ package name does not appear as 'LSubLibName' in
@@ -76,6 +129,18 @@ instance Binary Dependency
 instance Structured Dependency
 instance NFData Dependency where rnf = genericRnf
 
+instance Binary PrivateDependency
+instance Structured PrivateDependency
+instance NFData PrivateDependency where rnf = genericRnf
+
+instance Binary PrivateAlias
+instance Structured PrivateAlias
+instance NFData PrivateAlias where rnf = genericRnf
+
+instance Binary Dependencies
+instance Structured Dependencies
+instance NFData Dependencies where rnf = genericRnf
+
 -- |
 --
 -- >>> prettyShow $ Dependency (mkPackageName "pkg") anyVersion mainLibSet
@@ -139,6 +204,7 @@ instance Pretty Dependency where
 -- >>> map (`simpleParsec'` "mylib:sub") [CabalSpecV2_4, CabalSpecV3_0] :: [Maybe Dependency]
 -- [Nothing,Just (Dependency (PackageName "mylib") (OrLaterVersion (mkVersion [0])) (fromNonEmpty (LSubLibName (UnqualComponentName "sub") :| [])))]
 instance Parsec Dependency where
+  parsec :: forall m. CabalParsing m => m Dependency
   parsec = do
     name <- parsec
 
diff --git a/Cabal-syntax/src/Distribution/Types/Dependency/Lens.hs b/Cabal-syntax/src/Distribution/Types/Dependency/Lens.hs
new file mode 100644
index 00000000000..8dfb9d5bd27
--- /dev/null
+++ b/Cabal-syntax/src/Distribution/Types/Dependency/Lens.hs
@@ -0,0 +1,14 @@
+module Distribution.Types.Dependency.Lens
+  ( private_depends
+  ) where
+
+import Distribution.Compat.Lens
+import Distribution.Compat.Prelude
+import Prelude ()
+
+import Distribution.Types.Dependency (Dependency, PrivateDependency)
+
+import qualified Distribution.Types.Dependency as T
+
+private_depends :: Lens' PrivateDependency [Dependency]
+private_depends f d = fmap (\x -> d{T.private_depends = x}) (f (T.private_depends d))
diff --git a/Cabal-syntax/src/Distribution/Types/DependencyMap.hs b/Cabal-syntax/src/Distribution/Types/DependencyMap.hs
index aebca2c4cbf..8357155e16a 100644
--- a/Cabal-syntax/src/Distribution/Types/DependencyMap.hs
+++ b/Cabal-syntax/src/Distribution/Types/DependencyMap.hs
@@ -18,7 +18,7 @@ import qualified Data.Map.Lazy as Map
 
 -- | A map of dependencies.  Newtyped since the default monoid instance is not
 --   appropriate.  The monoid instance uses 'intersectVersionRanges'.
-newtype DependencyMap = DependencyMap {unDependencyMap :: Map PackageName (VersionRange, NonEmptySet LibraryName)}
+newtype DependencyMap = DependencyMap {unDependencyMap :: Map (PackageName, IsPrivate) (VersionRange, NonEmptySet LibraryName)}
   deriving (Show, Read, Eq)
 
 instance Monoid DependencyMap where
@@ -36,12 +36,22 @@ intersectVersionRangesAndJoinComponents
 intersectVersionRangesAndJoinComponents (va, ca) (vb, cb) =
   (intersectVersionRanges va vb, ca <> cb)
 
-toDepMap :: [Dependency] -> DependencyMap
+toDepMap :: Dependencies -> DependencyMap
 toDepMap ds =
-  DependencyMap $ Map.fromListWith intersectVersionRangesAndJoinComponents [(p, (vr, cs)) | Dependency p vr cs <- ds]
+  DependencyMap $
+    Map.fromListWith
+      intersectVersionRangesAndJoinComponents
+      ( [((p, Public), (vr, cs)) | Dependency p vr cs <- publicDependencies ds]
+          ++ [((p, Private pn), (vr, cs)) | PrivateDependency pn pds <- privateDependencies ds, Dependency p vr cs <- pds]
+      )
 
-fromDepMap :: DependencyMap -> [Dependency]
-fromDepMap m = [Dependency p vr cs | (p, (vr, cs)) <- Map.toList (unDependencyMap m)]
+fromDepMap :: DependencyMap -> Dependencies
+fromDepMap m =
+  Dependencies
+    [Dependency p vr cs | ((p, Public), (vr, cs)) <- Map.toList (unDependencyMap m)]
+    [PrivateDependency alias deps | (alias, deps) <- Map.toList priv_deps]
+  where
+    priv_deps = Map.fromListWith (++) [(sn, [Dependency p vr cs]) | ((p, (Private sn)), (vr, cs)) <- Map.toList (unDependencyMap m)]
 
 -- Apply extra constraints to a dependency map.
 -- Combines dependencies where the result will only contain keys from the left
@@ -54,6 +64,7 @@ constrainBy
 constrainBy = foldl' tightenConstraint
   where
     tightenConstraint (DependencyMap l) (PackageVersionConstraint pn vr) = DependencyMap $
-      case Map.lookup pn l of
+      -- TODO: Need to establish where these constraints come from
+      case Map.lookup (pn, Public) l of
         Nothing -> l
-        Just (vr', cs) -> Map.insert pn (intersectVersionRanges vr' vr, cs) l
+        Just (vr', cs) -> Map.insert (pn, Public) (intersectVersionRanges vr' vr, cs) l
diff --git a/Cabal-syntax/src/Distribution/Types/GenericPackageDescription.hs b/Cabal-syntax/src/Distribution/Types/GenericPackageDescription.hs
index 55ec8652304..312db47053b 100644
--- a/Cabal-syntax/src/Distribution/Types/GenericPackageDescription.hs
+++ b/Cabal-syntax/src/Distribution/Types/GenericPackageDescription.hs
@@ -44,30 +44,30 @@ data GenericPackageDescription = GenericPackageDescription
   --   Perfectly, PackageIndex should have sum type, so we don't need to
   --   have dummy GPDs.
   , genPackageFlags :: [PackageFlag]
-  , condLibrary :: Maybe (CondTree ConfVar [Dependency] Library)
+  , condLibrary :: Maybe (CondTree ConfVar Dependencies Library)
   , condSubLibraries
       :: [ ( UnqualComponentName
-           , CondTree ConfVar [Dependency] Library
+           , CondTree ConfVar Dependencies Library
            )
          ]
   , condForeignLibs
       :: [ ( UnqualComponentName
-           , CondTree ConfVar [Dependency] ForeignLib
+           , CondTree ConfVar Dependencies ForeignLib
            )
          ]
   , condExecutables
       :: [ ( UnqualComponentName
-           , CondTree ConfVar [Dependency] Executable
+           , CondTree ConfVar Dependencies Executable
            )
          ]
   , condTestSuites
       :: [ ( UnqualComponentName
-           , CondTree ConfVar [Dependency] TestSuite
+           , CondTree ConfVar Dependencies TestSuite
            )
          ]
   , condBenchmarks
       :: [ ( UnqualComponentName
-           , CondTree ConfVar [Dependency] Benchmark
+           , CondTree ConfVar Dependencies Benchmark
            )
          ]
   }
@@ -99,15 +99,15 @@ instance L.HasBuildInfos GenericPackageDescription where
       <*> (traverse . L._2 . traverseCondTreeBuildInfo) f x5
       <*> (traverse . L._2 . traverseCondTreeBuildInfo) f x6
 
--- We use this traversal to keep [Dependency] field in CondTree up to date.
+-- We use this traversal to keep Dependencies field in CondTree up to date.
 traverseCondTreeBuildInfo
   :: forall f comp v
    . (Applicative f, L.HasBuildInfo comp)
-  => LensLike' f (CondTree v [Dependency] comp) L.BuildInfo
+  => LensLike' f (CondTree v Dependencies comp) L.BuildInfo
 traverseCondTreeBuildInfo g = node
   where
-    mkCondNode :: comp -> [CondBranch v [Dependency] comp] -> CondTree v [Dependency] comp
-    mkCondNode comp = CondNode comp (view L.targetBuildDepends comp)
+    mkCondNode :: comp -> [CondBranch v Dependencies comp] -> CondTree v Dependencies comp
+    mkCondNode comp = CondNode comp (Dependencies (view L.targetBuildDepends comp) (view L.targetPrivateBuildDepends comp))
 
     node (CondNode comp _ branches) =
       mkCondNode
diff --git a/Cabal-syntax/src/Distribution/Types/GenericPackageDescription/Lens.hs b/Cabal-syntax/src/Distribution/Types/GenericPackageDescription/Lens.hs
index 213c97128f9..9d6ad5d2a2b 100644
--- a/Cabal-syntax/src/Distribution/Types/GenericPackageDescription/Lens.hs
+++ b/Cabal-syntax/src/Distribution/Types/GenericPackageDescription/Lens.hs
@@ -22,7 +22,7 @@ import Distribution.System (Arch, OS)
 import Distribution.Types.Benchmark (Benchmark)
 import Distribution.Types.CondTree (CondTree)
 import Distribution.Types.ConfVar (ConfVar (..))
-import Distribution.Types.Dependency (Dependency)
+import Distribution.Types.Dependency (Dependencies)
 import Distribution.Types.Executable (Executable)
 import Distribution.Types.Flag (FlagName, PackageFlag (MkPackageFlag))
 import Distribution.Types.ForeignLib (ForeignLib)
@@ -49,35 +49,35 @@ genPackageFlags :: Lens' GenericPackageDescription [PackageFlag]
 genPackageFlags f s = fmap (\x -> s{T.genPackageFlags = x}) (f (T.genPackageFlags s))
 {-# INLINE genPackageFlags #-}
 
-condLibrary :: Lens' GenericPackageDescription (Maybe (CondTree ConfVar [Dependency] Library))
+condLibrary :: Lens' GenericPackageDescription (Maybe (CondTree ConfVar Dependencies Library))
 condLibrary f s = fmap (\x -> s{T.condLibrary = x}) (f (T.condLibrary s))
 {-# INLINE condLibrary #-}
 
-condSubLibraries :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar [Dependency] Library))]
+condSubLibraries :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar Dependencies Library))]
 condSubLibraries f s = fmap (\x -> s{T.condSubLibraries = x}) (f (T.condSubLibraries s))
 {-# INLINE condSubLibraries #-}
 
-condForeignLibs :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar [Dependency] ForeignLib))]
+condForeignLibs :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar Dependencies ForeignLib))]
 condForeignLibs f s = fmap (\x -> s{T.condForeignLibs = x}) (f (T.condForeignLibs s))
 {-# INLINE condForeignLibs #-}
 
-condExecutables :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar [Dependency] Executable))]
+condExecutables :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar Dependencies Executable))]
 condExecutables f s = fmap (\x -> s{T.condExecutables = x}) (f (T.condExecutables s))
 {-# INLINE condExecutables #-}
 
-condTestSuites :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar [Dependency] TestSuite))]
+condTestSuites :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar Dependencies TestSuite))]
 condTestSuites f s = fmap (\x -> s{T.condTestSuites = x}) (f (T.condTestSuites s))
 {-# INLINE condTestSuites #-}
 
-condBenchmarks :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar [Dependency] Benchmark))]
+condBenchmarks :: Lens' GenericPackageDescription [(UnqualComponentName, (CondTree ConfVar Dependencies Benchmark))]
 condBenchmarks f s = fmap (\x -> s{T.condBenchmarks = x}) (f (T.condBenchmarks s))
 {-# INLINE condBenchmarks #-}
 
 allCondTrees
   :: Applicative f
   => ( forall a
-        . CondTree ConfVar [Dependency] a
-       -> f (CondTree ConfVar [Dependency] a)
+        . CondTree ConfVar Dependencies a
+       -> f (CondTree ConfVar Dependencies a)
      )
   -> GenericPackageDescription
   -> f GenericPackageDescription
diff --git a/Cabal-syntax/src/Distribution/Types/PackageDescription.hs b/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
index a3f1d0c33da..cec1014d222 100644
--- a/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
+++ b/Cabal-syntax/src/Distribution/Types/PackageDescription.hs
@@ -60,8 +60,6 @@ module Distribution.Types.PackageDescription
 import Distribution.Compat.Prelude
 import Prelude ()
 
-import Control.Monad ((<=<))
-
 -- lens
 
 import Distribution.Types.Benchmark
@@ -362,13 +360,20 @@ enabledBuildInfos pkg enabled =
 -- ------------------------------------------------------------
 
 -- | Get the combined build-depends entries of all components.
-allBuildDepends :: PackageDescription -> [Dependency]
-allBuildDepends = targetBuildDepends <=< allBuildInfo
+allBuildDepends :: PackageDescription -> [(Maybe PrivateAlias, Dependency)]
+allBuildDepends pd = do
+  bi <- allBuildInfo pd
+  [(Nothing, d) | d <- targetBuildDepends bi]
+    ++ [(Just p, d) | PrivateDependency p ds <- targetPrivateBuildDepends bi, d <- ds]
 
 -- | Get the combined build-depends entries of all enabled components, per the
 -- given request spec.
-enabledBuildDepends :: PackageDescription -> ComponentRequestedSpec -> [Dependency]
-enabledBuildDepends spec pd = targetBuildDepends =<< enabledBuildInfos spec pd
+enabledBuildDepends :: PackageDescription -> ComponentRequestedSpec -> [(Maybe PrivateAlias, Dependency)]
+enabledBuildDepends spec pd =
+  do
+    bi <- enabledBuildInfos spec pd
+    [(Nothing, d) | d <- targetBuildDepends bi]
+      ++ [(Just p, d) | PrivateDependency p ds <- targetPrivateBuildDepends bi, d <- ds]
 
 updatePackageDescription :: HookedBuildInfo -> PackageDescription -> PackageDescription
 updatePackageDescription (mb_lib_bi, exe_bi) p =
diff --git a/Cabal-tests/tests/NoThunks.hs b/Cabal-tests/tests/NoThunks.hs
index 6a81475dc03..9bc45114694 100644
--- a/Cabal-tests/tests/NoThunks.hs
+++ b/Cabal-tests/tests/NoThunks.hs
@@ -79,6 +79,9 @@ instance NoThunks ModuleReexport
 instance NoThunks LibraryVisibility
 instance NoThunks ForeignLibType
 instance NoThunks GenericPackageDescription
+instance NoThunks Dependencies
+instance NoThunks PrivateDependency
+instance NoThunks PrivateAlias
 instance NoThunks KnownRepoType
 instance NoThunks Library
 instance NoThunks LibraryName
diff --git a/Cabal-tests/tests/ParserTests/regressions/Octree-0.5.expr b/Cabal-tests/tests/ParserTests/regressions/Octree-0.5.expr
index 3d03421210b..14f8b716352 100644
--- a/Cabal-tests/tests/ParserTests/regressions/Octree-0.5.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/Octree-0.5.expr
@@ -154,26 +154,30 @@ GenericPackageDescription {
               (OrLaterVersion
                 (mkVersion [2, 4, 0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (IntersectVersionRanges
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [4, 0]))
+              (EarlierVersion
+                (mkVersion [4, 7])))
+            mainLibSet,
+          Dependency
+            (PackageName "AC-Vector")
             (OrLaterVersion
-              (mkVersion [4, 0]))
-            (EarlierVersion
-              (mkVersion [4, 7])))
-          mainLibSet,
-        Dependency
-          (PackageName "AC-Vector")
-          (OrLaterVersion
-            (mkVersion [2, 3, 0]))
-          mainLibSet,
-        Dependency
-          (PackageName "QuickCheck")
-          (OrLaterVersion
-            (mkVersion [2, 4, 0]))
-          mainLibSet],
+              (mkVersion [2, 3, 0]))
+            mainLibSet,
+          Dependency
+            (PackageName "QuickCheck")
+            (OrLaterVersion
+              (mkVersion [2, 4, 0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -260,27 +264,31 @@ GenericPackageDescription {
                 (OrLaterVersion
                   (mkVersion [2, 4, 0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (IntersectVersionRanges
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [4, 0]))
+                (EarlierVersion
+                  (mkVersion [4, 7])))
+              mainLibSet,
+            Dependency
+              (PackageName "AC-Vector")
               (OrLaterVersion
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-            mainLibSet,
-          Dependency
-            (PackageName "QuickCheck")
-            (OrLaterVersion
-              (mkVersion [2, 4, 0]))
-            mainLibSet],
+                (mkVersion [2, 3, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName "QuickCheck")
+              (OrLaterVersion
+                (mkVersion [2, 4, 0]))
+              mainLibSet],
+          privateDependencies = []},
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     _×_
       (UnqualComponentName "readme")
@@ -365,30 +373,34 @@ GenericPackageDescription {
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-          Dependency
-            (PackageName "base")
-            (IntersectVersionRanges
+        condTreeConstraints =
+        Dependencies {
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+              (PackageName "base")
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-              (mkVersion [2, 4, 0]))
-            mainLibSet,
-          Dependency
-            (PackageName "markdown-unlit")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+                (mkVersion [2, 3, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName "QuickCheck")
+              (OrLaterVersion
+                (mkVersion [2, 4, 0]))
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+            Dependency
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+              (OrLaterVersion (mkVersion [0]))
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diff --git a/Cabal-tests/tests/ParserTests/regressions/anynone.expr b/Cabal-tests/tests/ParserTests/regressions/anynone.expr
index 3191425d609..c28388a521e 100644
--- a/Cabal-tests/tests/ParserTests/regressions/anynone.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/anynone.expr
@@ -103,12 +103,16 @@ GenericPackageDescription {
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               mainLibSet],
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-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
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+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
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   condSubLibraries = [],
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diff --git a/Cabal-tests/tests/ParserTests/regressions/big-version.expr b/Cabal-tests/tests/ParserTests/regressions/big-version.expr
index e677de20626..baca580b38a 100644
--- a/Cabal-tests/tests/ParserTests/regressions/big-version.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/big-version.expr
@@ -100,8 +100,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
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-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
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+        privateDependencies = []},
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diff --git a/Cabal-tests/tests/ParserTests/regressions/common-conditional.expr b/Cabal-tests/tests/ParserTests/regressions/common-conditional.expr
index f6ffe291e59..c9ba4e6eed2 100644
--- a/Cabal-tests/tests/ParserTests/regressions/common-conditional.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/common-conditional.expr
@@ -120,12 +120,16 @@ GenericPackageDescription {
               (PackageName "ghc-prim")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
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           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "ghc-prim")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
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+          Dependency
+            (PackageName "ghc-prim")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
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@@ -203,20 +207,24 @@ GenericPackageDescription {
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-              Dependency
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-                    (mkVersion [4, 11])))
-                mainLibSet,
-              Dependency
-                (PackageName "containers")
-                (OrLaterVersion (mkVersion [0]))
-                mainLibSet],
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+            Dependencies {
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+                Dependency
+                  (PackageName "base")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
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+                    (EarlierVersion
+                      (mkVersion [4, 11])))
+                  mainLibSet,
+                Dependency
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+                  (OrLaterVersion (mkVersion [0]))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = [
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                 condBranchCondition =
@@ -286,12 +294,16 @@ GenericPackageDescription {
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                           (OrLaterVersion (mkVersion [0]))
                           mainLibSet],
+                      targetPrivateBuildDepends = [],
                       mixins = []}},
-                  condTreeConstraints = [
-                    Dependency
-                      (PackageName "Win32")
-                      (OrLaterVersion (mkVersion [0]))
-                      mainLibSet],
+                  condTreeConstraints =
+                  Dependencies {
+                    publicDependencies = [
+                      Dependency
+                        (PackageName "Win32")
+                        (OrLaterVersion (mkVersion [0]))
+                        mainLibSet],
+                    privateDependencies = []},
                   condTreeComponents = []},
                 condBranchIfFalse = Nothing}]},
           condBranchIfFalse = Nothing}]},
@@ -364,13 +376,17 @@ GenericPackageDescription {
                 (PackageName "HUnit")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
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           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "HUnit")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "HUnit")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = [
           CondBranch {
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@@ -436,9 +452,13 @@ GenericPackageDescription {
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                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing},
           CondBranch {
@@ -517,21 +537,25 @@ GenericPackageDescription {
                       (PackageName "containers")
                       (OrLaterVersion (mkVersion [0]))
                       mainLibSet],
+                  targetPrivateBuildDepends = [],
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                 testCodeGenerators = []},
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-                Dependency
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-                    (OrLaterVersion
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-                      (mkVersion [4, 11])))
-                  mainLibSet,
-                Dependency
-                  (PackageName "containers")
-                  (OrLaterVersion (mkVersion [0]))
-                  mainLibSet],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [
+                  Dependency
+                    (PackageName "base")
+                    (IntersectVersionRanges
+                      (OrLaterVersion
+                        (mkVersion [4, 10]))
+                      (EarlierVersion
+                        (mkVersion [4, 11])))
+                    mainLibSet,
+                  Dependency
+                    (PackageName "containers")
+                    (OrLaterVersion (mkVersion [0]))
+                    mainLibSet],
+                privateDependencies = []},
               condTreeComponents = [
                 CondBranch {
                   condBranchCondition =
@@ -601,13 +625,17 @@ GenericPackageDescription {
                             (PackageName "Win32")
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+                        targetPrivateBuildDepends = [],
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                       testCodeGenerators = []},
-                    condTreeConstraints = [
-                      Dependency
-                        (PackageName "Win32")
-                        (OrLaterVersion (mkVersion [0]))
-                        mainLibSet],
+                    condTreeConstraints =
+                    Dependencies {
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+                          (PackageName "Win32")
+                          (OrLaterVersion (mkVersion [0]))
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                 CondBranch {
@@ -678,13 +706,17 @@ GenericPackageDescription {
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-                    condTreeConstraints = [
-                      Dependency
-                        (PackageName "Win32")
-                        (OrLaterVersion (mkVersion [0]))
-                        mainLibSet],
+                    condTreeConstraints =
+                    Dependencies {
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+                          (PackageName "Win32")
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                   condBranchIfFalse = Nothing}]},
             condBranchIfFalse = Nothing}]}],
diff --git a/Cabal-tests/tests/ParserTests/regressions/common.expr b/Cabal-tests/tests/ParserTests/regressions/common.expr
index e0eb4a1dde7..955af0e2ca8 100644
--- a/Cabal-tests/tests/ParserTests/regressions/common.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/common.expr
@@ -118,12 +118,16 @@ GenericPackageDescription {
               (PackageName "ghc-prim")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "ghc-prim")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
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+          Dependency
+            (PackageName "ghc-prim")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -194,12 +198,16 @@ GenericPackageDescription {
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                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
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           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "HUnit")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "HUnit")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/common2.expr b/Cabal-tests/tests/ParserTests/regressions/common2.expr
index b3cb004eecb..83596f63a7b 100644
--- a/Cabal-tests/tests/ParserTests/regressions/common2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/common2.expr
@@ -126,24 +126,28 @@ GenericPackageDescription {
               (PackageName "ghc-prim")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
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-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "ghc-prim")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
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+          Dependency
+            (PackageName "base")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [4, 10]))
+              (EarlierVersion
+                (mkVersion [4, 11])))
+            mainLibSet,
+          Dependency
+            (PackageName "containers")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "ghc-prim")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -213,12 +217,16 @@ GenericPackageDescription {
                     (PackageName "Win32")
                     (OrLaterVersion (mkVersion [0]))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "Win32")
-                (OrLaterVersion (mkVersion [0]))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "Win32")
+                  (OrLaterVersion (mkVersion [0]))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing}]},
   condSubLibraries = [
@@ -305,24 +313,28 @@ GenericPackageDescription {
                 (PackageName "ghc-prim")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [4, 10]))
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-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "ghc-prim")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [4, 10]))
+                (EarlierVersion
+                  (mkVersion [4, 11])))
+              mainLibSet,
+            Dependency
+              (PackageName "containers")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "ghc-prim")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = [
           CondBranch {
             condBranchCondition =
@@ -394,12 +406,16 @@ GenericPackageDescription {
                       (PackageName "Win32")
                       (OrLaterVersion (mkVersion [0]))
                       mainLibSet],
+                  targetPrivateBuildDepends = [],
                   mixins = []}},
-              condTreeConstraints = [
-                Dependency
-                  (PackageName "Win32")
-                  (OrLaterVersion (mkVersion [0]))
-                  mainLibSet],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [
+                  Dependency
+                    (PackageName "Win32")
+                    (OrLaterVersion (mkVersion [0]))
+                    mainLibSet],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing}]}],
   condForeignLibs = [],
@@ -482,25 +498,29 @@ GenericPackageDescription {
                 (PackageName "HUnit")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
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-              (OrLaterVersion
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-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "HUnit")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
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+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [4, 10]))
+                (EarlierVersion
+                  (mkVersion [4, 11])))
+              mainLibSet,
+            Dependency
+              (PackageName "containers")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "HUnit")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = [
           CondBranch {
             condBranchCondition =
@@ -570,13 +590,17 @@ GenericPackageDescription {
                       (PackageName "Win32")
                       (OrLaterVersion (mkVersion [0]))
                       mainLibSet],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [
-                Dependency
-                  (PackageName "Win32")
-                  (OrLaterVersion (mkVersion [0]))
-                  mainLibSet],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [
+                  Dependency
+                    (PackageName "Win32")
+                    (OrLaterVersion (mkVersion [0]))
+                    mainLibSet],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing},
           CondBranch {
@@ -647,13 +671,17 @@ GenericPackageDescription {
                       (PackageName "Win32")
                       (OrLaterVersion (mkVersion [0]))
                       mainLibSet],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [
-                Dependency
-                  (PackageName "Win32")
-                  (OrLaterVersion (mkVersion [0]))
-                  mainLibSet],
+              condTreeConstraints =
+              Dependencies {
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+                  Dependency
+                    (PackageName "Win32")
+                    (OrLaterVersion (mkVersion [0]))
+                    mainLibSet],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing},
           CondBranch {
@@ -720,9 +748,13 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
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                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
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+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing}]}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/common3.expr b/Cabal-tests/tests/ParserTests/regressions/common3.expr
index 21b200baa7b..acad707bda7 100644
--- a/Cabal-tests/tests/ParserTests/regressions/common3.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/common3.expr
@@ -118,12 +118,16 @@ GenericPackageDescription {
               (PackageName "ghc-prim")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "ghc-prim")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
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+          Dependency
+            (PackageName "ghc-prim")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -206,24 +210,28 @@ GenericPackageDescription {
                 (PackageName "HUnit")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
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           testCodeGenerators = []},
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-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "HUnit")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
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+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
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+                (EarlierVersion
+                  (mkVersion [4, 11])))
+              mainLibSet,
+            Dependency
+              (PackageName "containers")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "HUnit")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/elif.expr b/Cabal-tests/tests/ParserTests/regressions/elif.expr
index 1315d689467..d22deddf324 100644
--- a/Cabal-tests/tests/ParserTests/regressions/elif.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/elif.expr
@@ -109,8 +109,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
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+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -180,12 +184,16 @@ GenericPackageDescription {
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                     (OrLaterVersion (mkVersion [0]))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "unix")
-                (OrLaterVersion (mkVersion [0]))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "unix")
+                  (OrLaterVersion (mkVersion [0]))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing}]},
   condSubLibraries = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/elif2.expr b/Cabal-tests/tests/ParserTests/regressions/elif2.expr
index 61f2177cbaa..ece3c44ab04 100644
--- a/Cabal-tests/tests/ParserTests/regressions/elif2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/elif2.expr
@@ -109,8 +109,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
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+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -180,12 +184,16 @@ GenericPackageDescription {
                     (PackageName "unix")
                     (OrLaterVersion (mkVersion [0]))
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+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "unix")
-                (OrLaterVersion (mkVersion [0]))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
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+                Dependency
+                  (PackageName "unix")
+                  (OrLaterVersion (mkVersion [0]))
+                  mainLibSet],
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             condTreeComponents = []},
           condBranchIfFalse = Just
             CondNode {
@@ -249,8 +257,12 @@ GenericPackageDescription {
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                   customFieldsBI = [],
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+                  targetPrivateBuildDepends = [],
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+              condTreeConstraints =
+              Dependencies {
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@@ -320,12 +332,16 @@ GenericPackageDescription {
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                             (OrLaterVersion (mkVersion [0]))
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-                    condTreeConstraints = [
-                      Dependency
-                        (PackageName "Win32")
-                        (OrLaterVersion (mkVersion [0]))
-                        mainLibSet],
+                    condTreeConstraints =
+                    Dependencies {
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+                          (PackageName "Win32")
+                          (OrLaterVersion (mkVersion [0]))
+                          mainLibSet],
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@@ -389,8 +405,12 @@ GenericPackageDescription {
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+                          targetPrivateBuildDepends = [],
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-                      condTreeConstraints = [],
+                      condTreeConstraints =
+                      Dependencies {
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diff --git a/Cabal-tests/tests/ParserTests/regressions/encoding-0.8.expr b/Cabal-tests/tests/ParserTests/regressions/encoding-0.8.expr
index e1b125e7a32..681892c14e0 100644
--- a/Cabal-tests/tests/ParserTests/regressions/encoding-0.8.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/encoding-0.8.expr
@@ -126,16 +126,20 @@ GenericPackageDescription {
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                   (mkVersion [4, 4])))
               mainLibSet],
+          targetPrivateBuildDepends = [],
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-      condTreeConstraints = [
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-          (UnionVersionRanges
-            (LaterVersion
-              (mkVersion [4, 4]))
-            (ThisVersion
-              (mkVersion [4, 4])))
-          mainLibSet],
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+        publicDependencies = [
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+              (ThisVersion
+                (mkVersion [4, 4])))
+            mainLibSet],
+        privateDependencies = []},
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diff --git a/Cabal-tests/tests/ParserTests/regressions/generics-sop.expr b/Cabal-tests/tests/ParserTests/regressions/generics-sop.expr
index 9084371a614..9d721e24db8 100644
--- a/Cabal-tests/tests/ParserTests/regressions/generics-sop.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/generics-sop.expr
@@ -278,40 +278,44 @@ GenericPackageDescription {
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               mainLibSet],
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-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [1, 3]))
-            (EarlierVersion
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+            (PackageName "template-haskell")
+            (IntersectVersionRanges
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+              (EarlierVersion
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+            mainLibSet,
+          Dependency
+            (PackageName "ghc-prim")
+            (IntersectVersionRanges
+              (OrLaterVersion
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+              (EarlierVersion
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+          Dependency
+            (PackageName "deepseq")
+            (IntersectVersionRanges
+              (OrLaterVersion
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+              (EarlierVersion
+                (mkVersion [1, 5])))
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@@ -385,16 +389,20 @@ GenericPackageDescription {
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-                (IntersectVersionRanges
-                  (OrLaterVersion
-                    (mkVersion [0, 7]))
-                  (EarlierVersion
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@@ -478,25 +486,29 @@ GenericPackageDescription {
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+                    (EarlierVersion
+                      (mkVersion [0, 6])))
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+                Dependency
+                  (PackageName "transformers")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
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+                    (EarlierVersion
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+                  mainLibSet],
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         CondBranch {
@@ -565,8 +577,12 @@ GenericPackageDescription {
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+                targetPrivateBuildDepends = [],
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-            condTreeConstraints = [],
+            condTreeConstraints =
+            Dependencies {
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+              privateDependencies = []},
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         CondBranch {
@@ -635,8 +651,12 @@ GenericPackageDescription {
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+            condTreeConstraints =
+            Dependencies {
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+              privateDependencies = []},
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@@ -721,21 +741,25 @@ GenericPackageDescription {
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-              (OrLaterVersion
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-              (EarlierVersion
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+              (PackageName "base")
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+              (IntersectVersionRanges
+                (OrLaterVersion
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+                (EarlierVersion
+                  (mkVersion [0, 14])))
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+              (OrLaterVersion (mkVersion [0]))
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diff --git a/Cabal-tests/tests/ParserTests/regressions/hasktorch.expr b/Cabal-tests/tests/ParserTests/regressions/hasktorch.expr
index 346af927d1b..a2cdde88871 100644
--- a/Cabal-tests/tests/ParserTests/regressions/hasktorch.expr
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@@ -398,80 +398,84 @@ GenericPackageDescription {
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+                (LaterVersion
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-          (IntersectVersionRanges
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-            (EarlierVersion
-              (mkVersion [0, 0, 2])))
-          mainLibSet],
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+            mainLibSet,
+          Dependency
+            (PackageName "hasktorch")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
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+                      "hasktorch-cpu")])),
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+            (PackageName "hasktorch-ffi-th")
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+              (UnionVersionRanges
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+                  (mkVersion [0, 0, 1]))
+                (LaterVersion
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+            (IntersectVersionRanges
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@@ -646,8 +650,12 @@ GenericPackageDescription {
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+            condTreeConstraints =
+            Dependencies {
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+              privateDependencies = []},
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         CondBranch {
@@ -897,17 +905,21 @@ GenericPackageDescription {
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-                    [
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+                  (PackageName "hasktorch")
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+                  (NonEmptySet.fromNonEmpty
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+                          (UnqualComponentName
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@@ -1088,8 +1100,12 @@ GenericPackageDescription {
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@@ -1535,6 +1551,7 @@ GenericPackageDescription {
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@@ -2582,100 +2599,103 @@ GenericPackageDescription {
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@@ -2744,8 +2764,12 @@ GenericPackageDescription {
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@@ -2842,6 +2866,7 @@ GenericPackageDescription {
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@@ -4840,16 +4865,19 @@ GenericPackageDescription {
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@@ -5193,6 +5221,7 @@ GenericPackageDescription {
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@@ -6242,124 +6271,127 @@ GenericPackageDescription {
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+              (UnionVersionRanges
+                (ThisVersion
+                  (mkVersion [2, 2, 2]))
+                (LaterVersion
+                  (mkVersion [2, 2, 2])))
+              mainLibSet,
+            Dependency
+              (PackageName
+                "microlens-platform")
+              (UnionVersionRanges
+                (ThisVersion
+                  (mkVersion [0, 3, 10]))
+                (LaterVersion
+                  (mkVersion [0, 3, 10])))
+              mainLibSet,
+            Dependency
+              (PackageName "monad-loops")
+              (UnionVersionRanges
+                (ThisVersion
+                  (mkVersion [0, 4, 3]))
+                (LaterVersion
+                  (mkVersion [0, 4, 3])))
+              mainLibSet,
+            Dependency
+              (PackageName "time")
+              (UnionVersionRanges
+                (ThisVersion
+                  (mkVersion [1, 8, 0]))
+                (LaterVersion
+                  (mkVersion [1, 8, 0])))
+              mainLibSet,
+            Dependency
+              (PackageName "transformers")
+              (UnionVersionRanges
+                (ThisVersion
+                  (mkVersion [0, 5, 5]))
+                (LaterVersion
+                  (mkVersion [0, 5, 5])))
+              mainLibSet,
+            Dependency
+              (PackageName "generic-lens")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/hidden-main-lib.expr b/Cabal-tests/tests/ParserTests/regressions/hidden-main-lib.expr
index fba99528b53..c341d178084 100644
--- a/Cabal-tests/tests/ParserTests/regressions/hidden-main-lib.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/hidden-main-lib.expr
@@ -105,12 +105,16 @@ GenericPackageDescription {
               (PackageName "base")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/indentation.expr b/Cabal-tests/tests/ParserTests/regressions/indentation.expr
index e5b106dc5cd..88a6c09c396 100644
--- a/Cabal-tests/tests/ParserTests/regressions/indentation.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/indentation.expr
@@ -110,8 +110,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/indentation2.expr b/Cabal-tests/tests/ParserTests/regressions/indentation2.expr
index 46f24105f0f..755195fc848 100644
--- a/Cabal-tests/tests/ParserTests/regressions/indentation2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/indentation2.expr
@@ -103,8 +103,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/indentation3.expr b/Cabal-tests/tests/ParserTests/regressions/indentation3.expr
index 0191d063f6e..db211c2be9c 100644
--- a/Cabal-tests/tests/ParserTests/regressions/indentation3.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/indentation3.expr
@@ -105,8 +105,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-5055.expr b/Cabal-tests/tests/ParserTests/regressions/issue-5055.expr
index 07c04ec6cb9..ee3554212a0 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-5055.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-5055.expr
@@ -112,16 +112,20 @@ GenericPackageDescription {
                   (EarlierVersion
                     (mkVersion [5])))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [4, 8]))
-              (EarlierVersion
-                (mkVersion [5])))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [4, 8]))
+                (EarlierVersion
+                  (mkVersion [5])))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [
     _×_
@@ -195,17 +199,21 @@ GenericPackageDescription {
                   (EarlierVersion
                     (mkVersion [5])))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [4, 8]))
-              (EarlierVersion
-                (mkVersion [5])))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [4, 8]))
+                (EarlierVersion
+                  (mkVersion [5])))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = [
           CondBranch {
             condBranchCondition =
@@ -271,9 +279,13 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing}]}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-5846.expr b/Cabal-tests/tests/ParserTests/regressions/issue-5846.expr
index 2ff7de7917e..86bdde11186 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-5846.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-5846.expr
@@ -134,44 +134,48 @@ GenericPackageDescription {
                       (UnqualComponentName "a"),
                     LSubLibName
                       (UnqualComponentName "b")]))],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "lib1")
-          (OrLaterVersion (mkVersion [0]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName "a"),
-                LSubLibName
-                  (UnqualComponentName "b")])),
-        Dependency
-          (PackageName "lib2")
-          (OrLaterVersion (mkVersion [0]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName "c")])),
-        Dependency
-          (PackageName "lib3")
-          (OrLaterVersion (mkVersion [1]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName "d")])),
-        Dependency
-          (PackageName "lib4")
-          (OrLaterVersion (mkVersion [1]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName "a"),
-                LSubLibName
-                  (UnqualComponentName "b")]))],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "lib1")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName "a"),
+                  LSubLibName
+                    (UnqualComponentName "b")])),
+          Dependency
+            (PackageName "lib2")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName "c")])),
+          Dependency
+            (PackageName "lib3")
+            (OrLaterVersion (mkVersion [1]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName "d")])),
+          Dependency
+            (PackageName "lib4")
+            (OrLaterVersion (mkVersion [1]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName "a"),
+                  LSubLibName
+                    (UnqualComponentName "b")]))],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-6083-a.expr b/Cabal-tests/tests/ParserTests/regressions/issue-6083-a.expr
index 43c345dd170..3d5861da196 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-6083-a.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-6083-a.expr
@@ -111,21 +111,25 @@ GenericPackageDescription {
                     LSubLibName
                       (UnqualComponentName
                         "sublib")]))],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "issue")
-          (OrLaterVersion (mkVersion [0]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName
-                    "sublib")]))],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "issue")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName
+                      "sublib")]))],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [
     _×_
@@ -193,8 +197,12 @@ GenericPackageDescription {
             PerCompilerFlavor [] [],
             customFieldsBI = [],
             targetBuildDepends = [],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [],
+          privateDependencies = []},
         condTreeComponents = []}],
   condForeignLibs = [],
   condExecutables = [
@@ -267,16 +275,20 @@ GenericPackageDescription {
                 (PackageName "sublib")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "sublib")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "sublib")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []},
     _×_
       (UnqualComponentName "demo-b")
@@ -352,21 +364,25 @@ GenericPackageDescription {
                       LSubLibName
                         (UnqualComponentName
                           "sublib")]))],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            (NonEmptySet.fromNonEmpty
-              (NE.fromList
-                [
-                  LSubLibName
-                    (UnqualComponentName
-                      "sublib")]))],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              (NonEmptySet.fromNonEmpty
+                (NE.fromList
+                  [
+                    LSubLibName
+                      (UnqualComponentName
+                        "sublib")]))],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-6083-b.expr b/Cabal-tests/tests/ParserTests/regressions/issue-6083-b.expr
index e6606851627..7de6fff480d 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-6083-b.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-6083-b.expr
@@ -111,21 +111,25 @@ GenericPackageDescription {
                     LSubLibName
                       (UnqualComponentName
                         "sublib")]))],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "issue")
-          (OrLaterVersion (mkVersion [0]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName
-                    "sublib")]))],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "issue")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName
+                      "sublib")]))],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [
     _×_
@@ -193,8 +197,12 @@ GenericPackageDescription {
             PerCompilerFlavor [] [],
             customFieldsBI = [],
             targetBuildDepends = [],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [],
+          privateDependencies = []},
         condTreeComponents = []}],
   condForeignLibs = [],
   condExecutables = [
@@ -272,21 +280,25 @@ GenericPackageDescription {
                       LSubLibName
                         (UnqualComponentName
                           "sublib")]))],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            (NonEmptySet.fromNonEmpty
-              (NE.fromList
-                [
-                  LSubLibName
-                    (UnqualComponentName
-                      "sublib")]))],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              (NonEmptySet.fromNonEmpty
+                (NE.fromList
+                  [
+                    LSubLibName
+                      (UnqualComponentName
+                        "sublib")]))],
+          privateDependencies = []},
         condTreeComponents = []},
     _×_
       (UnqualComponentName "demo-b")
@@ -362,21 +374,25 @@ GenericPackageDescription {
                       LSubLibName
                         (UnqualComponentName
                           "sublib")]))],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "issue")
-            (OrLaterVersion (mkVersion [0]))
-            (NonEmptySet.fromNonEmpty
-              (NE.fromList
-                [
-                  LSubLibName
-                    (UnqualComponentName
-                      "sublib")]))],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "issue")
+              (OrLaterVersion (mkVersion [0]))
+              (NonEmptySet.fromNonEmpty
+                (NE.fromList
+                  [
+                    LSubLibName
+                      (UnqualComponentName
+                        "sublib")]))],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-6083-c.expr b/Cabal-tests/tests/ParserTests/regressions/issue-6083-c.expr
index 7435b0d59b4..aaafb65ceed 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-6083-c.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-6083-c.expr
@@ -111,21 +111,25 @@ GenericPackageDescription {
                     LSubLibName
                       (UnqualComponentName
                         "sublib")]))],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "issue")
-          (OrLaterVersion (mkVersion [0]))
-          (NonEmptySet.fromNonEmpty
-            (NE.fromList
-              [
-                LSubLibName
-                  (UnqualComponentName
-                    "sublib")]))],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "issue")
+            (OrLaterVersion (mkVersion [0]))
+            (NonEmptySet.fromNonEmpty
+              (NE.fromList
+                [
+                  LSubLibName
+                    (UnqualComponentName
+                      "sublib")]))],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [
     _×_
@@ -193,8 +197,12 @@ GenericPackageDescription {
             PerCompilerFlavor [] [],
             customFieldsBI = [],
             targetBuildDepends = [],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [],
+          privateDependencies = []},
         condTreeComponents = []}],
   condForeignLibs = [],
   condExecutables = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-6083-pkg-pkg.expr b/Cabal-tests/tests/ParserTests/regressions/issue-6083-pkg-pkg.expr
index a221632efa4..bd946d92f0d 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-6083-pkg-pkg.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-6083-pkg-pkg.expr
@@ -106,16 +106,20 @@ GenericPackageDescription {
               (PackageName "freetype")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "freetype")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "freetype")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "freetype")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "freetype")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/issue-774.expr b/Cabal-tests/tests/ParserTests/regressions/issue-774.expr
index e1ffb85dceb..eb23ebfb0b0 100644
--- a/Cabal-tests/tests/ParserTests/regressions/issue-774.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/issue-774.expr
@@ -112,8 +112,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/jaeger-flamegraph.expr b/Cabal-tests/tests/ParserTests/regressions/jaeger-flamegraph.expr
index c9e675ceb76..d4dacada3a3 100644
--- a/Cabal-tests/tests/ParserTests/regressions/jaeger-flamegraph.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/jaeger-flamegraph.expr
@@ -156,21 +156,25 @@ GenericPackageDescription {
               (MajorBoundVersion
                 (mkVersion [2, 12, 6, 1]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (UnionVersionRanges
-            (MajorBoundVersion
-              (mkVersion [4, 11, 1, 0]))
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (UnionVersionRanges
+              (MajorBoundVersion
+                (mkVersion [4, 11, 1, 0]))
+              (MajorBoundVersion
+                (mkVersion [4, 12, 0, 0])))
+            mainLibSet,
+          Dependency
+            (PackageName "QuickCheck")
             (MajorBoundVersion
-              (mkVersion [4, 12, 0, 0])))
-          mainLibSet,
-        Dependency
-          (PackageName "QuickCheck")
-          (MajorBoundVersion
-            (mkVersion [2, 12, 6, 1]))
-          mainLibSet],
+              (mkVersion [2, 12, 6, 1]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -286,52 +290,56 @@ GenericPackageDescription {
                 (MajorBoundVersion
                   (mkVersion [1, 2, 3, 1]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (UnionVersionRanges
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (UnionVersionRanges
+                (MajorBoundVersion
+                  (mkVersion [4, 11, 1, 0]))
+                (MajorBoundVersion
+                  (mkVersion [4, 12, 0, 0])))
+              mainLibSet,
+            Dependency
+              (PackageName
+                "jaeger-flamegraph")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "bytestring")
               (MajorBoundVersion
-                (mkVersion [4, 11, 1, 0]))
+                (mkVersion [0, 10, 8, 2]))
+              mainLibSet,
+            Dependency
+              (PackageName "containers")
               (MajorBoundVersion
-                (mkVersion [4, 12, 0, 0])))
-            mainLibSet,
-          Dependency
-            (PackageName
-              "jaeger-flamegraph")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "bytestring")
-            (MajorBoundVersion
-              (mkVersion [0, 10, 8, 2]))
-            mainLibSet,
-          Dependency
-            (PackageName "containers")
-            (MajorBoundVersion
-              (mkVersion [0, 6, 0, 1]))
-            mainLibSet,
-          Dependency
-            (PackageName "extra")
-            (MajorBoundVersion
-              (mkVersion [1, 6, 13]))
-            mainLibSet,
-          Dependency
-            (PackageName "aeson")
-            (MajorBoundVersion
-              (mkVersion [1, 4, 1, 0]))
-            mainLibSet,
-          Dependency
-            (PackageName
-              "optparse-applicative")
-            (MajorBoundVersion
-              (mkVersion [0, 14, 3, 0]))
-            mainLibSet,
-          Dependency
-            (PackageName "text")
-            (MajorBoundVersion
-              (mkVersion [1, 2, 3, 1]))
-            mainLibSet],
+                (mkVersion [0, 6, 0, 1]))
+              mainLibSet,
+            Dependency
+              (PackageName "extra")
+              (MajorBoundVersion
+                (mkVersion [1, 6, 13]))
+              mainLibSet,
+            Dependency
+              (PackageName "aeson")
+              (MajorBoundVersion
+                (mkVersion [1, 4, 1, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName
+                "optparse-applicative")
+              (MajorBoundVersion
+                (mkVersion [0, 14, 3, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName "text")
+              (MajorBoundVersion
+                (mkVersion [1, 2, 3, 1]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [
     _×_
@@ -435,36 +443,40 @@ GenericPackageDescription {
                 (MajorBoundVersion
                   (mkVersion [0, 10]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (UnionVersionRanges
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (UnionVersionRanges
+                (MajorBoundVersion
+                  (mkVersion [4, 11, 1, 0]))
+                (MajorBoundVersion
+                  (mkVersion [4, 12, 0, 0])))
+              mainLibSet,
+            Dependency
+              (PackageName
+                "jaeger-flamegraph")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "tasty")
               (MajorBoundVersion
-                (mkVersion [4, 11, 1, 0]))
+                (mkVersion [1, 1, 0, 4]))
+              mainLibSet,
+            Dependency
+              (PackageName "tasty-hspec")
               (MajorBoundVersion
-                (mkVersion [4, 12, 0, 0])))
-            mainLibSet,
-          Dependency
-            (PackageName
-              "jaeger-flamegraph")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "tasty")
-            (MajorBoundVersion
-              (mkVersion [1, 1, 0, 4]))
-            mainLibSet,
-          Dependency
-            (PackageName "tasty-hspec")
-            (MajorBoundVersion
-              (mkVersion [1, 1, 5]))
-            mainLibSet,
-          Dependency
-            (PackageName "tasty-quickcheck")
-            (MajorBoundVersion
-              (mkVersion [0, 10]))
-            mainLibSet],
+                (mkVersion [1, 1, 5]))
+              mainLibSet,
+            Dependency
+              (PackageName "tasty-quickcheck")
+              (MajorBoundVersion
+                (mkVersion [0, 10]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/leading-comma-2.expr b/Cabal-tests/tests/ParserTests/regressions/leading-comma-2.expr
index 0bb5556b2f4..d71b1d8604e 100644
--- a/Cabal-tests/tests/ParserTests/regressions/leading-comma-2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/leading-comma-2.expr
@@ -132,32 +132,36 @@ GenericPackageDescription {
               (PackageName "directory")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "containers")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "deepseq")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "transformers")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "filepath")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "directory")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "containers")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "deepseq")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "transformers")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "filepath")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "directory")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/leading-comma.expr b/Cabal-tests/tests/ParserTests/regressions/leading-comma.expr
index b1ba1b282f4..7a166677823 100644
--- a/Cabal-tests/tests/ParserTests/regressions/leading-comma.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/leading-comma.expr
@@ -125,32 +125,36 @@ GenericPackageDescription {
               (PackageName "directory")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "containers")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "deepseq")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "transformers")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "filepath")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "directory")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "containers")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "deepseq")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "transformers")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "filepath")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "directory")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/libpq1.expr b/Cabal-tests/tests/ParserTests/regressions/libpq1.expr
index 8906a91f63b..8e097892041 100644
--- a/Cabal-tests/tests/ParserTests/regressions/libpq1.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/libpq1.expr
@@ -210,24 +210,28 @@ GenericPackageDescription {
                 (EarlierVersion
                   (mkVersion [0, 11])))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [4, 3]))
-            (EarlierVersion
-              (mkVersion [4, 13])))
-          mainLibSet,
-        Dependency
-          (PackageName "bytestring")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 9, 1, 0]))
-            (EarlierVersion
-              (mkVersion [0, 11])))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [4, 3]))
+              (EarlierVersion
+                (mkVersion [4, 13])))
+            mainLibSet,
+          Dependency
+            (PackageName "bytestring")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 9, 1, 0]))
+              (EarlierVersion
+                (mkVersion [0, 11])))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -301,16 +305,20 @@ GenericPackageDescription {
                       (EarlierVersion
                         (mkVersion [2, 8])))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "unix")
-                (IntersectVersionRanges
-                  (OrLaterVersion
-                    (mkVersion [2, 4, 2, 0]))
-                  (EarlierVersion
-                    (mkVersion [2, 8])))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "unix")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
+                      (mkVersion [2, 4, 2, 0]))
+                    (EarlierVersion
+                      (mkVersion [2, 8])))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing},
         CondBranch {
@@ -385,16 +393,20 @@ GenericPackageDescription {
                       (EarlierVersion
                         (mkVersion [2, 7])))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "Win32")
-                (IntersectVersionRanges
-                  (OrLaterVersion
-                    (mkVersion [2, 2, 0, 2]))
-                  (EarlierVersion
-                    (mkVersion [2, 7])))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "Win32")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
+                      (mkVersion [2, 2, 0, 2]))
+                    (EarlierVersion
+                      (mkVersion [2, 7])))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing},
         CondBranch {
@@ -468,8 +480,12 @@ GenericPackageDescription {
                 PerCompilerFlavor [] [],
                 customFieldsBI = [],
                 targetBuildDepends = [],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Just
             CondNode {
@@ -533,8 +549,12 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []}},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = [
                 CondBranch {
                   condBranchCondition =
@@ -600,8 +620,12 @@ GenericPackageDescription {
                         PerCompilerFlavor [] [],
                         customFieldsBI = [],
                         targetBuildDepends = [],
+                        targetPrivateBuildDepends = [],
                         mixins = []}},
-                    condTreeConstraints = [],
+                    condTreeConstraints =
+                    Dependencies {
+                      publicDependencies = [],
+                      privateDependencies = []},
                     condTreeComponents = []},
                   condBranchIfFalse = Just
                     CondNode {
@@ -665,8 +689,12 @@ GenericPackageDescription {
                           PerCompilerFlavor [] [],
                           customFieldsBI = [],
                           targetBuildDepends = [],
+                          targetPrivateBuildDepends = [],
                           mixins = []}},
-                      condTreeConstraints = [],
+                      condTreeConstraints =
+                      Dependencies {
+                        publicDependencies = [],
+                        privateDependencies = []},
                       condTreeComponents = [
                         CondBranch {
                           condBranchCondition =
@@ -732,8 +760,12 @@ GenericPackageDescription {
                                 PerCompilerFlavor [] [],
                                 customFieldsBI = [],
                                 targetBuildDepends = [],
+                                targetPrivateBuildDepends = [],
                                 mixins = []}},
-                            condTreeConstraints = [],
+                            condTreeConstraints =
+                            Dependencies {
+                              publicDependencies = [],
+                              privateDependencies = []},
                             condTreeComponents = []},
                           condBranchIfFalse =
                           Nothing}]}}]}}]},
diff --git a/Cabal-tests/tests/ParserTests/regressions/libpq2.expr b/Cabal-tests/tests/ParserTests/regressions/libpq2.expr
index 3c26ece45ad..12539463cc4 100644
--- a/Cabal-tests/tests/ParserTests/regressions/libpq2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/libpq2.expr
@@ -215,24 +215,28 @@ GenericPackageDescription {
                 (EarlierVersion
                   (mkVersion [0, 11])))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [4, 3]))
-            (EarlierVersion
-              (mkVersion [4, 13])))
-          mainLibSet,
-        Dependency
-          (PackageName "bytestring")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 9, 1, 0]))
-            (EarlierVersion
-              (mkVersion [0, 11])))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [4, 3]))
+              (EarlierVersion
+                (mkVersion [4, 13])))
+            mainLibSet,
+          Dependency
+            (PackageName "bytestring")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 9, 1, 0]))
+              (EarlierVersion
+                (mkVersion [0, 11])))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -306,16 +310,20 @@ GenericPackageDescription {
                       (EarlierVersion
                         (mkVersion [2, 8])))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "unix")
-                (IntersectVersionRanges
-                  (OrLaterVersion
-                    (mkVersion [2, 4, 2, 0]))
-                  (EarlierVersion
-                    (mkVersion [2, 8])))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "unix")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
+                      (mkVersion [2, 4, 2, 0]))
+                    (EarlierVersion
+                      (mkVersion [2, 8])))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing},
         CondBranch {
@@ -390,16 +398,20 @@ GenericPackageDescription {
                       (EarlierVersion
                         (mkVersion [2, 7])))
                     mainLibSet],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [
-              Dependency
-                (PackageName "Win32")
-                (IntersectVersionRanges
-                  (OrLaterVersion
-                    (mkVersion [2, 2, 0, 2]))
-                  (EarlierVersion
-                    (mkVersion [2, 7])))
-                mainLibSet],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [
+                Dependency
+                  (PackageName "Win32")
+                  (IntersectVersionRanges
+                    (OrLaterVersion
+                      (mkVersion [2, 2, 0, 2]))
+                    (EarlierVersion
+                      (mkVersion [2, 7])))
+                  mainLibSet],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing},
         CondBranch {
@@ -470,8 +482,12 @@ GenericPackageDescription {
                 PerCompilerFlavor [] [],
                 customFieldsBI = [],
                 targetBuildDepends = [],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Just
             CondNode {
@@ -535,8 +551,12 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []}},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = [
                 CondBranch {
                   condBranchCondition =
@@ -602,8 +622,12 @@ GenericPackageDescription {
                         PerCompilerFlavor [] [],
                         customFieldsBI = [],
                         targetBuildDepends = [],
+                        targetPrivateBuildDepends = [],
                         mixins = []}},
-                    condTreeConstraints = [],
+                    condTreeConstraints =
+                    Dependencies {
+                      publicDependencies = [],
+                      privateDependencies = []},
                     condTreeComponents = []},
                   condBranchIfFalse = Just
                     CondNode {
@@ -667,8 +691,12 @@ GenericPackageDescription {
                           PerCompilerFlavor [] [],
                           customFieldsBI = [],
                           targetBuildDepends = [],
+                          targetPrivateBuildDepends = [],
                           mixins = []}},
-                      condTreeConstraints = [],
+                      condTreeConstraints =
+                      Dependencies {
+                        publicDependencies = [],
+                        privateDependencies = []},
                       condTreeComponents = [
                         CondBranch {
                           condBranchCondition =
@@ -734,8 +762,12 @@ GenericPackageDescription {
                                 PerCompilerFlavor [] [],
                                 customFieldsBI = [],
                                 targetBuildDepends = [],
+                                targetPrivateBuildDepends = [],
                                 mixins = []}},
-                            condTreeConstraints = [],
+                            condTreeConstraints =
+                            Dependencies {
+                              publicDependencies = [],
+                              privateDependencies = []},
                             condTreeComponents = []},
                           condBranchIfFalse =
                           Nothing}]}}]}}]},
diff --git a/Cabal-tests/tests/ParserTests/regressions/mixin-1.expr b/Cabal-tests/tests/ParserTests/regressions/mixin-1.expr
index de8a15f04c0..27e23d6650f 100644
--- a/Cabal-tests/tests/ParserTests/regressions/mixin-1.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/mixin-1.expr
@@ -114,6 +114,7 @@ GenericPackageDescription {
                 (PackageName "str-bytestring")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = [
               Mixin {
                 mixinPackageName = PackageName
@@ -143,19 +144,22 @@ GenericPackageDescription {
                         (ModuleName "Str.ByteString")],
                   includeRequiresRn =
                   DefaultRenaming}}]}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-string")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-bytestring")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-string")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-bytestring")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/mixin-2.expr b/Cabal-tests/tests/ParserTests/regressions/mixin-2.expr
index 3bf06bc9c3b..e0ff2fcb192 100644
--- a/Cabal-tests/tests/ParserTests/regressions/mixin-2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/mixin-2.expr
@@ -114,6 +114,7 @@ GenericPackageDescription {
                 (PackageName "str-bytestring")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = [
               Mixin {
                 mixinPackageName = PackageName
@@ -143,19 +144,22 @@ GenericPackageDescription {
                         (ModuleName "Str.ByteString")],
                   includeRequiresRn =
                   DefaultRenaming}}]}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-string")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-bytestring")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-string")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-bytestring")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/mixin-3.expr b/Cabal-tests/tests/ParserTests/regressions/mixin-3.expr
index 0c0fc57a8b8..d89df8b451d 100644
--- a/Cabal-tests/tests/ParserTests/regressions/mixin-3.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/mixin-3.expr
@@ -114,6 +114,7 @@ GenericPackageDescription {
                 (PackageName "str-bytestring")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = [
               Mixin {
                 mixinPackageName = PackageName
@@ -126,19 +127,22 @@ GenericPackageDescription {
                     [ModuleName "Foo"],
                   includeRequiresRn =
                   DefaultRenaming}}]}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-string")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-bytestring")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-string")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-bytestring")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/monad-param.expr b/Cabal-tests/tests/ParserTests/regressions/monad-param.expr
index 28d57c1e3b0..296104ef38b 100644
--- a/Cabal-tests/tests/ParserTests/regressions/monad-param.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/monad-param.expr
@@ -136,20 +136,24 @@ GenericPackageDescription {
               (PackageName "stm")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "mtl")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "stm")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "mtl")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "stm")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
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diff --git a/Cabal-tests/tests/ParserTests/regressions/multiple-libs-2.expr b/Cabal-tests/tests/ParserTests/regressions/multiple-libs-2.expr
index a8c6b0c0c4a..48b5264673c 100644
--- a/Cabal-tests/tests/ParserTests/regressions/multiple-libs-2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/multiple-libs-2.expr
@@ -105,12 +105,16 @@ GenericPackageDescription {
               (PackageName "base")
               (OrLaterVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [
     _×_
@@ -183,12 +187,16 @@ GenericPackageDescription {
                 (PackageName "base")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condForeignLibs = [],
   condExecutables = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/noVersion.expr b/Cabal-tests/tests/ParserTests/regressions/noVersion.expr
index 8187272c2c0..f4f99c23bb3 100644
--- a/Cabal-tests/tests/ParserTests/regressions/noVersion.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/noVersion.expr
@@ -105,12 +105,16 @@ GenericPackageDescription {
               (PackageName "bad-package")
               (EarlierVersion (mkVersion [0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "bad-package")
-          (EarlierVersion (mkVersion [0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "bad-package")
+            (EarlierVersion (mkVersion [0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/nothing-unicode.expr b/Cabal-tests/tests/ParserTests/regressions/nothing-unicode.expr
index 2f2663733c6..74501fb3845 100644
--- a/Cabal-tests/tests/ParserTests/regressions/nothing-unicode.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/nothing-unicode.expr
@@ -116,8 +116,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = [
         CondBranch {
           condBranchCondition =
@@ -183,8 +187,12 @@ GenericPackageDescription {
                 PerCompilerFlavor [] [],
                 customFieldsBI = [],
                 targetBuildDepends = [],
+                targetPrivateBuildDepends = [],
                 mixins = []}},
-            condTreeConstraints = [],
+            condTreeConstraints =
+            Dependencies {
+              publicDependencies = [],
+              privateDependencies = []},
             condTreeComponents = []},
           condBranchIfFalse = Nothing}]},
   condSubLibraries = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/shake.expr b/Cabal-tests/tests/ParserTests/regressions/shake.expr
index 8dd849d75bd..5099b41c052 100644
--- a/Cabal-tests/tests/ParserTests/regressions/shake.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/shake.expr
@@ -383,81 +383,85 @@ GenericPackageDescription {
               (OrLaterVersion
                 (mkVersion [1, 1]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
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-          (OrLaterVersion
-            (mkVersion [4, 5]))
-          mainLibSet,
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-          mainLibSet,
-        Dependency
-          (PackageName "deepseq")
-          (OrLaterVersion
-            (mkVersion [1, 1]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
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+            (PackageName "base")
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+              (mkVersion [4, 5]))
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+            (PackageName "directory")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "hashable")
+            (OrLaterVersion
+              (mkVersion [1, 1, 2, 3]))
+            mainLibSet,
+          Dependency
+            (PackageName "binary")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "filepath")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "process")
+            (OrLaterVersion
+              (mkVersion [1, 1]))
+            mainLibSet,
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+            (PackageName
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+            (OrLaterVersion
+              (mkVersion [0, 2, 1]))
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+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "utf8-string")
+            (OrLaterVersion
+              (mkVersion [0, 3]))
+            mainLibSet,
+          Dependency
+            (PackageName "time")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "random")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "js-jquery")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "js-flot")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "transformers")
+            (OrLaterVersion
+              (mkVersion [0, 2]))
+            mainLibSet,
+          Dependency
+            (PackageName "extra")
+            (OrLaterVersion
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+            mainLibSet,
+          Dependency
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+            (OrLaterVersion
+              (mkVersion [1, 1]))
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@@ -523,8 +527,12 @@ GenericPackageDescription {
                 PerCompilerFlavor [] [],
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+            condTreeConstraints =
+            Dependencies {
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@@ -594,12 +602,16 @@ GenericPackageDescription {
                           (PackageName "old-time")
                           (OrLaterVersion (mkVersion [0]))
                           mainLibSet],
+                      targetPrivateBuildDepends = [],
                       mixins = []}},
-                  condTreeConstraints = [
-                    Dependency
-                      (PackageName "old-time")
-                      (OrLaterVersion (mkVersion [0]))
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                 condBranchIfFalse = Nothing}]},
           condBranchIfFalse = Just
@@ -664,8 +676,12 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
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                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
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+              condTreeConstraints =
+              Dependencies {
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@@ -736,13 +752,17 @@ GenericPackageDescription {
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-                      Dependency
-                        (PackageName "unix")
-                        (OrLaterVersion
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+                    Dependencies {
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+                          (PackageName "unix")
+                          (OrLaterVersion
+                            (mkVersion [2, 5, 1]))
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@@ -813,12 +833,16 @@ GenericPackageDescription {
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                     (OrLaterVersion (mkVersion [0]))
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-            condTreeConstraints = [
-              Dependency
-                (PackageName "unix")
-                (OrLaterVersion (mkVersion [0]))
-                mainLibSet],
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   condSubLibraries = [],
@@ -1065,87 +1089,91 @@ GenericPackageDescription {
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                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
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@@ -1210,8 +1238,12 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
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-              condTreeConstraints = [],
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@@ -1275,8 +1307,12 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
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@@ -1343,12 +1379,16 @@ GenericPackageDescription {
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                             (OrLaterVersion (mkVersion [0]))
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+                        targetPrivateBuildDepends = [],
                         mixins = []}},
-                    condTreeConstraints = [
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-                        (PackageName "old-time")
-                        (OrLaterVersion (mkVersion [0]))
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@@ -1410,8 +1450,12 @@ GenericPackageDescription {
                     PerCompilerFlavor [] [],
                     customFieldsBI = [],
                     targetBuildDepends = [],
+                    targetPrivateBuildDepends = [],
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@@ -1479,13 +1523,17 @@ GenericPackageDescription {
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@@ -1553,12 +1601,16 @@ GenericPackageDescription {
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   condTestSuites = [
@@ -1848,89 +1900,93 @@ GenericPackageDescription {
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@@ -1996,9 +2052,13 @@ GenericPackageDescription {
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@@ -2065,9 +2125,13 @@ GenericPackageDescription {
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                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing},
           CondBranch {
@@ -2134,9 +2198,13 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = [
                 CondBranch {
                   condBranchCondition =
@@ -2206,13 +2274,17 @@ GenericPackageDescription {
                             (PackageName "old-time")
                             (OrLaterVersion (mkVersion [0]))
                             mainLibSet],
+                        targetPrivateBuildDepends = [],
                         mixins = []},
                       testCodeGenerators = []},
-                    condTreeConstraints = [
-                      Dependency
-                        (PackageName "old-time")
-                        (OrLaterVersion (mkVersion [0]))
-                        mainLibSet],
+                    condTreeConstraints =
+                    Dependencies {
+                      publicDependencies = [
+                        Dependency
+                          (PackageName "old-time")
+                          (OrLaterVersion (mkVersion [0]))
+                          mainLibSet],
+                      privateDependencies = []},
                     condTreeComponents = []},
                   condBranchIfFalse = Nothing}]},
             condBranchIfFalse = Just
@@ -2277,9 +2349,13 @@ GenericPackageDescription {
                     PerCompilerFlavor [] [],
                     customFieldsBI = [],
                     targetBuildDepends = [],
+                    targetPrivateBuildDepends = [],
                     mixins = []},
                   testCodeGenerators = []},
-                condTreeConstraints = [],
+                condTreeConstraints =
+                Dependencies {
+                  publicDependencies = [],
+                  privateDependencies = []},
                 condTreeComponents = [
                   CondBranch {
                     condBranchCondition =
@@ -2350,14 +2426,18 @@ GenericPackageDescription {
                               (OrLaterVersion
                                 (mkVersion [2, 5, 1]))
                               mainLibSet],
+                          targetPrivateBuildDepends = [],
                           mixins = []},
                         testCodeGenerators = []},
-                      condTreeConstraints = [
-                        Dependency
-                          (PackageName "unix")
-                          (OrLaterVersion
-                            (mkVersion [2, 5, 1]))
-                          mainLibSet],
+                      condTreeConstraints =
+                      Dependencies {
+                        publicDependencies = [
+                          Dependency
+                            (PackageName "unix")
+                            (OrLaterVersion
+                              (mkVersion [2, 5, 1]))
+                            mainLibSet],
+                        privateDependencies = []},
                       condTreeComponents = []},
                     condBranchIfFalse = Nothing}]}},
           CondBranch {
@@ -2428,13 +2508,17 @@ GenericPackageDescription {
                       (PackageName "unix")
                       (OrLaterVersion (mkVersion [0]))
                       mainLibSet],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [
-                Dependency
-                  (PackageName "unix")
-                  (OrLaterVersion (mkVersion [0]))
-                  mainLibSet],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [
+                  Dependency
+                    (PackageName "unix")
+                    (OrLaterVersion (mkVersion [0]))
+                    mainLibSet],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing}]}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/spdx-1.expr b/Cabal-tests/tests/ParserTests/regressions/spdx-1.expr
index 2ca07bf2322..a4b5453730b 100644
--- a/Cabal-tests/tests/ParserTests/regressions/spdx-1.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/spdx-1.expr
@@ -99,8 +99,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/spdx-2.expr b/Cabal-tests/tests/ParserTests/regressions/spdx-2.expr
index 9c50edd4864..c4bdcfb0c1c 100644
--- a/Cabal-tests/tests/ParserTests/regressions/spdx-2.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/spdx-2.expr
@@ -103,8 +103,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/spdx-3.expr b/Cabal-tests/tests/ParserTests/regressions/spdx-3.expr
index 944faa4c0c0..53abd4ed448 100644
--- a/Cabal-tests/tests/ParserTests/regressions/spdx-3.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/spdx-3.expr
@@ -103,8 +103,12 @@ GenericPackageDescription {
           PerCompilerFlavor [] [],
           customFieldsBI = [],
           targetBuildDepends = [],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/th-lift-instances.expr b/Cabal-tests/tests/ParserTests/regressions/th-lift-instances.expr
index 8f2edf09a36..dd59047de84 100644
--- a/Cabal-tests/tests/ParserTests/regressions/th-lift-instances.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/th-lift-instances.expr
@@ -180,57 +180,61 @@ GenericPackageDescription {
                 (EarlierVersion
                   (mkVersion [0, 11])))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [4, 4]))
-            (EarlierVersion
-              (mkVersion [5])))
-          mainLibSet,
-        Dependency
-          (PackageName "template-haskell")
-          (EarlierVersion
-            (mkVersion [2, 10]))
-          mainLibSet,
-        Dependency
-          (PackageName "th-lift")
-          (OrLaterVersion (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "containers")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 4]))
-            (EarlierVersion
-              (mkVersion [0, 6])))
-          mainLibSet,
-        Dependency
-          (PackageName "vector")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 9]))
-            (EarlierVersion
-              (mkVersion [0, 11])))
-          mainLibSet,
-        Dependency
-          (PackageName "text")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 11]))
-            (EarlierVersion
-              (mkVersion [1, 3])))
-          mainLibSet,
-        Dependency
-          (PackageName "bytestring")
-          (IntersectVersionRanges
-            (OrLaterVersion
-              (mkVersion [0, 9]))
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [4, 4]))
+              (EarlierVersion
+                (mkVersion [5])))
+            mainLibSet,
+          Dependency
+            (PackageName "template-haskell")
             (EarlierVersion
-              (mkVersion [0, 11])))
-          mainLibSet],
+              (mkVersion [2, 10]))
+            mainLibSet,
+          Dependency
+            (PackageName "th-lift")
+            (OrLaterVersion (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "containers")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 4]))
+              (EarlierVersion
+                (mkVersion [0, 6])))
+            mainLibSet,
+          Dependency
+            (PackageName "vector")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 9]))
+              (EarlierVersion
+                (mkVersion [0, 11])))
+            mainLibSet,
+          Dependency
+            (PackageName "text")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 11]))
+              (EarlierVersion
+                (mkVersion [1, 3])))
+            mainLibSet,
+          Dependency
+            (PackageName "bytestring")
+            (IntersectVersionRanges
+              (OrLaterVersion
+                (mkVersion [0, 9]))
+              (EarlierVersion
+                (mkVersion [0, 11])))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -356,63 +360,67 @@ GenericPackageDescription {
                   (EarlierVersion
                     (mkVersion [2, 8])))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "template-haskell")
-            (EarlierVersion
-              (mkVersion [2, 10]))
-            mainLibSet,
-          Dependency
-            (PackageName "containers")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [0, 4]))
-              (EarlierVersion
-                (mkVersion [0, 6])))
-            mainLibSet,
-          Dependency
-            (PackageName "vector")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [0, 9]))
-              (EarlierVersion
-                (mkVersion [0, 11])))
-            mainLibSet,
-          Dependency
-            (PackageName "text")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [0, 11]))
-              (EarlierVersion
-                (mkVersion [1, 2])))
-            mainLibSet,
-          Dependency
-            (PackageName "bytestring")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [0, 9]))
-              (EarlierVersion
-                (mkVersion [0, 11])))
-            mainLibSet,
-          Dependency
-            (PackageName
-              "th-lift-instances")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "QuickCheck")
-            (IntersectVersionRanges
-              (OrLaterVersion
-                (mkVersion [2, 6]))
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "template-haskell")
               (EarlierVersion
-                (mkVersion [2, 8])))
-            mainLibSet],
+                (mkVersion [2, 10]))
+              mainLibSet,
+            Dependency
+              (PackageName "containers")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [0, 4]))
+                (EarlierVersion
+                  (mkVersion [0, 6])))
+              mainLibSet,
+            Dependency
+              (PackageName "vector")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [0, 9]))
+                (EarlierVersion
+                  (mkVersion [0, 11])))
+              mainLibSet,
+            Dependency
+              (PackageName "text")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [0, 11]))
+                (EarlierVersion
+                  (mkVersion [1, 2])))
+              mainLibSet,
+            Dependency
+              (PackageName "bytestring")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [0, 9]))
+                (EarlierVersion
+                  (mkVersion [0, 11])))
+              mainLibSet,
+            Dependency
+              (PackageName
+                "th-lift-instances")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "QuickCheck")
+              (IntersectVersionRanges
+                (OrLaterVersion
+                  (mkVersion [2, 6]))
+                (EarlierVersion
+                  (mkVersion [2, 8])))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []},
     _×_
       (UnqualComponentName "doctests")
@@ -495,27 +503,31 @@ GenericPackageDescription {
                 (PackageName "filepath")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []},
           testCodeGenerators = []},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet,
-          Dependency
-            (PackageName "directory")
-            (OrLaterVersion
-              (mkVersion [1, 0]))
-            mainLibSet,
-          Dependency
-            (PackageName "doctest")
-            (OrLaterVersion
-              (mkVersion [0, 9, 1]))
-            mainLibSet,
-          Dependency
-            (PackageName "filepath")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet,
+            Dependency
+              (PackageName "directory")
+              (OrLaterVersion
+                (mkVersion [1, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName "doctest")
+              (OrLaterVersion
+                (mkVersion [0, 9, 1]))
+              mainLibSet,
+            Dependency
+              (PackageName "filepath")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = [
           CondBranch {
             condBranchCondition =
@@ -581,9 +593,13 @@ GenericPackageDescription {
                   PerCompilerFlavor [] [],
                   customFieldsBI = [],
                   targetBuildDepends = [],
+                  targetPrivateBuildDepends = [],
                   mixins = []},
                 testCodeGenerators = []},
-              condTreeConstraints = [],
+              condTreeConstraints =
+              Dependencies {
+                publicDependencies = [],
+                privateDependencies = []},
               condTreeComponents = []},
             condBranchIfFalse = Nothing}]}],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/ParserTests/regressions/version-sets.expr b/Cabal-tests/tests/ParserTests/regressions/version-sets.expr
index b134e4584ad..1d3277c8b33 100644
--- a/Cabal-tests/tests/ParserTests/regressions/version-sets.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/version-sets.expr
@@ -189,72 +189,76 @@ GenericPackageDescription {
                 (MajorBoundVersion
                   (mkVersion [2, 2, 0, 0])))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "network")
-          (MajorBoundVersion
-            (mkVersion [0]))
-          mainLibSet,
-        Dependency
-          (PackageName "base")
-          (ThisVersion (mkVersion [1]))
-          mainLibSet,
-        Dependency
-          (PackageName "base")
-          (ThisVersion (mkVersion [1]))
-          mainLibSet,
-        Dependency
-          (PackageName "base")
-          (UnionVersionRanges
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "network")
+            (MajorBoundVersion
+              (mkVersion [0]))
+            mainLibSet,
+          Dependency
+            (PackageName "base")
             (ThisVersion (mkVersion [1]))
-            (ThisVersion (mkVersion [2])))
-          mainLibSet,
-        Dependency
-          (PackageName "base")
-          (ThisVersion (mkVersion [1, 2]))
-          mainLibSet,
-        Dependency
-          (PackageName "base")
-          (UnionVersionRanges
+            mainLibSet,
+          Dependency
+            (PackageName "base")
+            (ThisVersion (mkVersion [1]))
+            mainLibSet,
+          Dependency
+            (PackageName "base")
+            (UnionVersionRanges
+              (ThisVersion (mkVersion [1]))
+              (ThisVersion (mkVersion [2])))
+            mainLibSet,
+          Dependency
+            (PackageName "base")
             (ThisVersion (mkVersion [1, 2]))
-            (ThisVersion
-              (mkVersion [3, 4])))
-          mainLibSet,
-        Dependency
-          (PackageName "ghc")
-          (UnionVersionRanges
-            (ThisVersion
-              (mkVersion [8, 6, 3]))
+            mainLibSet,
+          Dependency
+            (PackageName "base")
+            (UnionVersionRanges
+              (ThisVersion (mkVersion [1, 2]))
+              (ThisVersion
+                (mkVersion [3, 4])))
+            mainLibSet,
+          Dependency
+            (PackageName "ghc")
             (UnionVersionRanges
               (ThisVersion
-                (mkVersion [8, 4, 4]))
+                (mkVersion [8, 6, 3]))
               (UnionVersionRanges
                 (ThisVersion
-                  (mkVersion [8, 2, 2]))
+                  (mkVersion [8, 4, 4]))
                 (UnionVersionRanges
                   (ThisVersion
-                    (mkVersion [8, 0, 2]))
+                    (mkVersion [8, 2, 2]))
                   (UnionVersionRanges
                     (ThisVersion
-                      (mkVersion [7, 10, 3]))
+                      (mkVersion [8, 0, 2]))
                     (UnionVersionRanges
                       (ThisVersion
-                        (mkVersion [7, 8, 4]))
+                        (mkVersion [7, 10, 3]))
                       (UnionVersionRanges
                         (ThisVersion
-                          (mkVersion [7, 6, 3]))
-                        (ThisVersion
-                          (mkVersion [7, 4, 2])))))))))
-          mainLibSet,
-        Dependency
-          (PackageName "Cabal")
-          (UnionVersionRanges
-            (MajorBoundVersion
-              (mkVersion [2, 4, 1, 1]))
-            (MajorBoundVersion
-              (mkVersion [2, 2, 0, 0])))
-          mainLibSet],
+                          (mkVersion [7, 8, 4]))
+                        (UnionVersionRanges
+                          (ThisVersion
+                            (mkVersion [7, 6, 3]))
+                          (ThisVersion
+                            (mkVersion [7, 4, 2])))))))))
+            mainLibSet,
+          Dependency
+            (PackageName "Cabal")
+            (UnionVersionRanges
+              (MajorBoundVersion
+                (mkVersion [2, 4, 1, 1]))
+              (MajorBoundVersion
+                (mkVersion [2, 2, 0, 0])))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
diff --git a/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.expr b/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.expr
index 03959b195c0..ebd5e41d199 100644
--- a/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.expr
+++ b/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.expr
@@ -127,17 +127,21 @@ GenericPackageDescription {
               (OrLaterVersion
                 (mkVersion [0, 1, 0, 0]))
               mainLibSet],
+          targetPrivateBuildDepends = [],
           mixins = []}},
-      condTreeConstraints = [
-        Dependency
-          (PackageName "base")
-          (EarlierVersion (mkVersion [5]))
-          mainLibSet,
-        Dependency
-          (PackageName "str-sig")
-          (OrLaterVersion
-            (mkVersion [0, 1, 0, 0]))
-          mainLibSet],
+      condTreeConstraints =
+      Dependencies {
+        publicDependencies = [
+          Dependency
+            (PackageName "base")
+            (EarlierVersion (mkVersion [5]))
+            mainLibSet,
+          Dependency
+            (PackageName "str-sig")
+            (OrLaterVersion
+              (mkVersion [0, 1, 0, 0]))
+            mainLibSet],
+        privateDependencies = []},
       condTreeComponents = []},
   condSubLibraries = [],
   condForeignLibs = [],
@@ -219,21 +223,25 @@ GenericPackageDescription {
                 (PackageName "wl-pprint-indef")
                 (OrLaterVersion (mkVersion [0]))
                 mainLibSet],
+            targetPrivateBuildDepends = [],
             mixins = []}},
-        condTreeConstraints = [
-          Dependency
-            (PackageName "base")
-            (EarlierVersion (mkVersion [5]))
-            mainLibSet,
-          Dependency
-            (PackageName "str-string")
-            (OrLaterVersion
-              (mkVersion [0, 1, 0, 0]))
-            mainLibSet,
-          Dependency
-            (PackageName "wl-pprint-indef")
-            (OrLaterVersion (mkVersion [0]))
-            mainLibSet],
+        condTreeConstraints =
+        Dependencies {
+          publicDependencies = [
+            Dependency
+              (PackageName "base")
+              (EarlierVersion (mkVersion [5]))
+              mainLibSet,
+            Dependency
+              (PackageName "str-string")
+              (OrLaterVersion
+                (mkVersion [0, 1, 0, 0]))
+              mainLibSet,
+            Dependency
+              (PackageName "wl-pprint-indef")
+              (OrLaterVersion (mkVersion [0]))
+              mainLibSet],
+          privateDependencies = []},
         condTreeComponents = []}],
   condTestSuites = [],
   condBenchmarks = []}
diff --git a/Cabal-tests/tests/UnitTests/Distribution/Described.hs b/Cabal-tests/tests/UnitTests/Distribution/Described.hs
index 2c73c805c71..4e041c6d380 100644
--- a/Cabal-tests/tests/UnitTests/Distribution/Described.hs
+++ b/Cabal-tests/tests/UnitTests/Distribution/Described.hs
@@ -12,7 +12,7 @@ import Test.Tasty             (TestTree, testGroup)
 import Distribution.Compiler                       (CompilerFlavor, CompilerId)
 import Distribution.ModuleName                     (ModuleName)
 import Distribution.System                         (Arch, OS)
-import Distribution.Types.Dependency               (Dependency)
+import Distribution.Types.Dependency               (Dependency, PrivateDependency)
 import Distribution.Types.Flag                     (FlagAssignment, FlagName)
 import Distribution.Types.IncludeRenaming          (IncludeRenaming)
 import Distribution.Types.Mixin                    (Mixin)
@@ -30,6 +30,7 @@ import Test.QuickCheck.Instances.Cabal ()
 tests :: TestTree
 tests = testGroup "Described"
     [ testDescribed (Proxy :: Proxy Dependency)
+    , testDescribed (Proxy :: Proxy PrivateDependency)
     , testDescribed (Proxy :: Proxy PackageName)
     , testDescribed (Proxy :: Proxy PackageIdentifier)
     , testDescribed (Proxy :: Proxy PackageVersionConstraint)
diff --git a/Cabal-tests/tests/UnitTests/Distribution/Utils/Structured.hs b/Cabal-tests/tests/UnitTests/Distribution/Utils/Structured.hs
index 71653353f9f..4075b608e85 100644
--- a/Cabal-tests/tests/UnitTests/Distribution/Utils/Structured.hs
+++ b/Cabal-tests/tests/UnitTests/Distribution/Utils/Structured.hs
@@ -33,15 +33,15 @@ md5Check proxy md5Int = structureHash proxy @?= md5FromInteger md5Int
 md5CheckGenericPackageDescription :: Proxy GenericPackageDescription -> Assertion
 md5CheckGenericPackageDescription proxy = md5Check proxy
 #if MIN_VERSION_base(4,19,0)
-    0x5a48c6570cbcf96af4c51f38962e37b5
+    0x3d55bd418cd0619715252020b5490032
 #else
-    0xc5c0e54b95e651216e92db04c9cd4ecf
+    0xd049fb2803ff57821436895040ea4403
 #endif
 
 md5CheckLocalBuildInfo :: Proxy LocalBuildInfo -> Assertion
 md5CheckLocalBuildInfo proxy = md5Check proxy
 #if MIN_VERSION_base(4,19,0)
-    0x6d668de33d7b4d5df3830e65e6941373
+    0x6075b2e1ec83e58e6cf21c43781b38ec
 #else
-    0xcdf740970a7d37e5e7ca48ea5f4f25eb7
+    0x61579c843fbfefef0df2c5c65ef6bc9f
 #endif
diff --git a/Cabal-tree-diff/src/Data/TreeDiff/Instances/Cabal.hs b/Cabal-tree-diff/src/Data/TreeDiff/Instances/Cabal.hs
index 15fae62649e..863eaac1fb4 100644
--- a/Cabal-tree-diff/src/Data/TreeDiff/Instances/Cabal.hs
+++ b/Cabal-tree-diff/src/Data/TreeDiff/Instances/Cabal.hs
@@ -71,6 +71,8 @@ instance ToExpr CabalSpecVersion
 instance ToExpr CompilerFlavor
 instance ToExpr CompilerId
 instance ToExpr ComponentId
+instance ToExpr ComponentName
+instance ToExpr NotLibComponentName
 instance ToExpr DebugInfoLevel
 instance ToExpr DefUnitId
 instance ToExpr DumpBuildInfo
@@ -127,5 +129,8 @@ instance ToExpr UnqualComponentName
 instance ToExpr Verbosity
 instance ToExpr VerbosityFlag
 instance ToExpr VerbosityLevel
+instance ToExpr Dependencies
+instance ToExpr PrivateDependency
+instance ToExpr PrivateAlias
 
 instance ToExpr ShortText where toExpr = toExpr . fromShortText
diff --git a/Cabal/src/Distribution/Backpack/ComponentsGraph.hs b/Cabal/src/Distribution/Backpack/ComponentsGraph.hs
index aef3db817c6..0c7cb6a18ca 100644
--- a/Cabal/src/Distribution/Backpack/ComponentsGraph.hs
+++ b/Cabal/src/Distribution/Backpack/ComponentsGraph.hs
@@ -73,7 +73,7 @@ mkComponentsGraph enabled pkg_descr =
         toolDependencies = CExeName <$> getAllInternalToolDependencies pkg_descr bi
 
         libDependencies = do
-          Dependency pkgname _ lns <- targetBuildDepends bi
+          Dependency pkgname _ lns <- (targetBuildDepends bi ++ concatMap private_depends (targetPrivateBuildDepends bi))
           guard (pkgname == packageName pkg_descr)
 
           ln <- NES.toList lns
diff --git a/Cabal/src/Distribution/Backpack/Configure.hs b/Cabal/src/Distribution/Backpack/Configure.hs
index 8e9eb18ae6a..43b75db0408 100644
--- a/Cabal/src/Distribution/Backpack/Configure.hs
+++ b/Cabal/src/Distribution/Backpack/Configure.hs
@@ -103,7 +103,7 @@ configureComponentLocalBuildInfos
     let conf_pkg_map =
           Map.fromListWith
             Map.union
-            [ ( pc_pkgname pkg
+            [ ( (pc_pkgname pkg, pc_alias pkg)
               , Map.singleton
                   (pc_compname pkg)
                   ( AnnotatedId
@@ -117,8 +117,10 @@ configureComponentLocalBuildInfos
             ]
             `Map.union` Map.fromListWith
               Map.union
-              [ (pkg, Map.singleton (ann_cname aid) aid)
-              | PromisedComponent pkg aid <- promisedPkgDeps
+              [ ( (pkg, alias)
+                , Map.singleton (ann_cname aid) aid
+                )
+              | PromisedComponent pkg aid alias <- promisedPkgDeps
               ]
     graph1 <-
       toConfiguredComponents
@@ -151,7 +153,7 @@ configureComponentLocalBuildInfos
                   , emptyModuleShape
                   )
                 )
-              | PromisedComponent _ aid <- promisedPkgDeps
+              | PromisedComponent _ aid _ <- promisedPkgDeps
               ]
         uid_lookup def_uid
           | Just pkg <- PackageIndex.lookupUnitId installedPackageSet uid =
diff --git a/Cabal/src/Distribution/Backpack/ConfiguredComponent.hs b/Cabal/src/Distribution/Backpack/ConfiguredComponent.hs
index 9bfaefb7e0b..a542bc98dcb 100644
--- a/Cabal/src/Distribution/Backpack/ConfiguredComponent.hs
+++ b/Cabal/src/Distribution/Backpack/ConfiguredComponent.hs
@@ -100,7 +100,7 @@ dispConfiguredComponent cc =
 mkConfiguredComponent
   :: PackageDescription
   -> ComponentId
-  -> [AnnotatedId ComponentId] -- lib deps
+  -> [(AnnotatedId ComponentId, Maybe PrivateAlias)] -- lib deps
   -> [AnnotatedId ComponentId] -- exe deps
   -> Component
   -> LogProgress ConfiguredComponent
@@ -120,6 +120,8 @@ mkConfiguredComponent pkg_descr this_cid lib_deps exe_deps component = do
         { ci_ann_id = aid
         , ci_renaming = rns
         , ci_implicit = False
+        , -- Mixins can't be private
+          ci_alias = Nothing
         }
 
   -- Any @build-depends@ which is not explicitly mentioned in
@@ -127,14 +129,15 @@ mkConfiguredComponent pkg_descr this_cid lib_deps exe_deps component = do
   let used_explicitly = Set.fromList (map ci_id explicit_includes)
       implicit_includes =
         map
-          ( \aid ->
+          ( \(aid, alias) ->
               ComponentInclude
                 { ci_ann_id = aid
                 , ci_renaming = defaultIncludeRenaming
                 , ci_implicit = True
+                , ci_alias = alias
                 }
           )
-          $ filter (flip Set.notMember used_explicitly . ann_id) lib_deps
+          $ filter (flip Set.notMember used_explicitly . ann_id . fst) lib_deps
 
   return
     ConfiguredComponent
@@ -161,13 +164,14 @@ mkConfiguredComponent pkg_descr this_cid lib_deps exe_deps component = do
     deps_map =
       Map.fromList
         [ ((packageName dep, ann_cname dep), dep)
-        | dep <- lib_deps
+        | (dep, _) <- lib_deps
         ]
 
     is_public = componentName component == CLibName LMainLibName
 
+-- A function from PackageName -> Maybe PrivateQualifier -> ComponentName -> ResolvedComponentId
 type ConfiguredComponentMap =
-  Map PackageName (Map ComponentName (AnnotatedId ComponentId))
+  Map (PackageName, Maybe PrivateAlias) (Map ComponentName ((AnnotatedId ComponentId)))
 
 toConfiguredComponent
   :: PackageDescription
@@ -180,14 +184,16 @@ toConfiguredComponent pkg_descr this_cid lib_dep_map exe_dep_map component = do
   lib_deps <-
     if newPackageDepsBehaviour pkg_descr
       then fmap concat $
-        forM (targetBuildDepends bi) $
-          \(Dependency name _ sublibs) -> do
-            case Map.lookup name lib_dep_map of
+        forM ([(d, Nothing) | d <- targetBuildDepends bi] ++ [(d, Just alias) | (PrivateDependency alias ds) <- targetPrivateBuildDepends bi, d <- ds]) $
+          \((Dependency name _ sublibs), alias) -> do
+            case Map.lookup (name, alias) lib_dep_map of
               Nothing ->
                 dieProgress $
                   text "Dependency on unbuildable"
                     <+> text "package"
                     <+> pretty name
+                    <+> maybe mempty pretty alias
+                    <+> text (show lib_dep_map)
               Just pkg -> do
                 -- Return all library components
                 forM (NonEmptySet.toList sublibs) $ \lib ->
@@ -199,7 +205,8 @@ toConfiguredComponent pkg_descr this_cid lib_dep_map exe_dep_map component = do
                               <+> text (showLibraryName lib)
                               <+> text "from"
                               <+> pretty name
-                        Just v -> return v
+                              <+> maybe mempty pretty alias
+                        Just v -> return (v, alias)
       else return old_style_lib_deps
   mkConfiguredComponent
     pkg_descr
@@ -217,8 +224,8 @@ toConfiguredComponent pkg_descr this_cid lib_dep_map exe_dep_map component = do
     -- because it would imply a cyclic dependency for the
     -- library itself.
     old_style_lib_deps =
-      [ e
-      | (pn, comp_map) <- Map.toList lib_dep_map
+      [ (e, alias)
+      | ((pn, alias), comp_map) <- Map.toList lib_dep_map
       , pn /= packageName pkg_descr
       , (cn, e) <- Map.toList comp_map
       , cn == CLibName LMainLibName
@@ -236,7 +243,7 @@ toConfiguredComponent pkg_descr this_cid lib_dep_map exe_dep_map component = do
         -- which the package is attempting to use (those deps are only
         -- fed in when cabal-install uses this codepath.)
         -- TODO: Let cabal-install request errors here
-        Just exe <- [Map.lookup (CExeName cn) =<< Map.lookup pn exe_dep_map]
+        Just exe <- [Map.lookup (CExeName cn) =<< Map.lookup (pn, Nothing) exe_dep_map]
         ]
 
 -- | Also computes the 'ComponentId', and sets cc_public if necessary.
@@ -292,7 +299,7 @@ extendConfiguredComponentMap
 extendConfiguredComponentMap cc =
   Map.insertWith
     Map.union
-    (pkgName (cc_pkgid cc))
+    ((pkgName (cc_pkgid cc)), Nothing)
     (Map.singleton (cc_name cc) (cc_ann_id cc))
 
 -- Compute the 'ComponentId's for a graph of 'Component's.  The
diff --git a/Cabal/src/Distribution/Backpack/LinkedComponent.hs b/Cabal/src/Distribution/Backpack/LinkedComponent.hs
index b2d2bc25066..924945d0cb9 100644
--- a/Cabal/src/Distribution/Backpack/LinkedComponent.hs
+++ b/Cabal/src/Distribution/Backpack/LinkedComponent.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 
@@ -150,13 +151,14 @@ toLinkedComponent
             _ -> ([], [], [])
       src_hidden = otherModules (componentBuildInfo component)
 
+      -- HERE??
       -- Take each included ComponentId and resolve it into an
       -- \*unlinked* unit identity.  We will use unification (relying
       -- on the ModuleShape) to resolve these into linked identities.
       unlinked_includes :: [ComponentInclude (OpenUnitId, ModuleShape) IncludeRenaming]
       unlinked_includes =
-        [ ComponentInclude (fmap lookupUid dep_aid) rns i
-        | ComponentInclude dep_aid rns i <- cid_includes
+        [ ComponentInclude (fmap lookupUid dep_aid) rns i alias
+        | ComponentInclude dep_aid rns i alias <- cid_includes
         ]
 
       lookupUid :: ComponentId -> (OpenUnitId, ModuleShape)
@@ -184,7 +186,7 @@ toLinkedComponent
               , preModShapeRequires = Set.fromList src_reqs
               }
               : [ renamePreModuleShape (toPreModuleShape sh) rns
-                | ComponentInclude (AnnotatedId{ann_id = (_, sh)}) rns _ <- unlinked_includes
+                | ComponentInclude (AnnotatedId{ann_id = (_, sh)}) rns _ _ <- unlinked_includes
                 ]
         reqs = preModShapeRequires pre_shape
         insts =
@@ -236,7 +238,7 @@ toLinkedComponent
         -- src_reqs_u <- traverse convertReq src_reqs
         -- Read out all the final results by converting back
         -- into a pure representation.
-        let convertIncludeU (ComponentInclude dep_aid rns i) = do
+        let convertIncludeU (ComponentInclude dep_aid rns i alias) = do
               let component_name = pretty $ ann_cname dep_aid
               uid <- convertUnitIdU (ann_id dep_aid) component_name
               return
@@ -244,6 +246,7 @@ toLinkedComponent
                     { ci_ann_id = dep_aid{ann_id = uid}
                     , ci_renaming = rns
                     , ci_implicit = i
+                    , ci_alias = alias
                     }
                 )
 
diff --git a/Cabal/src/Distribution/Backpack/ModuleScope.hs b/Cabal/src/Distribution/Backpack/ModuleScope.hs
index 5e18766a15d..40b68513149 100644
--- a/Cabal/src/Distribution/Backpack/ModuleScope.hs
+++ b/Cabal/src/Distribution/Backpack/ModuleScope.hs
@@ -70,6 +70,7 @@ data ModuleScope = ModuleScope
   { modScopeProvides :: ModuleProvides
   , modScopeRequires :: ModuleRequires
   }
+  deriving (Show)
 
 -- | An empty 'ModuleScope'.
 emptyModuleScope :: ModuleScope
@@ -92,6 +93,7 @@ data ModuleSource
   | FromExposedModules ModuleName
   | FromOtherModules ModuleName
   | FromSignatures ModuleName
+  deriving (Show)
 
 -- We don't have line numbers, but if we did, we'd want to record that
 -- too
@@ -123,7 +125,7 @@ dispComponent pn cn =
 
 -- | An 'OpenModule', annotated with where it came from in a Cabal file.
 data WithSource a = WithSource ModuleSource a
-  deriving (Functor, Foldable, Traversable)
+  deriving (Show, Functor, Foldable, Traversable)
 
 unWithSource :: WithSource a -> a
 unWithSource (WithSource _ x) = x
diff --git a/Cabal/src/Distribution/Backpack/PreExistingComponent.hs b/Cabal/src/Distribution/Backpack/PreExistingComponent.hs
index 5f937de9062..aeca962b299 100644
--- a/Cabal/src/Distribution/Backpack/PreExistingComponent.hs
+++ b/Cabal/src/Distribution/Backpack/PreExistingComponent.hs
@@ -27,6 +27,7 @@ import Distribution.Types.AnnotatedId
 data PromisedComponent = PromisedComponent
   { pr_pkgname :: PackageName
   , pr_cid :: AnnotatedId ComponentId
+  , pr_alias :: Maybe PrivateAlias
   }
 
 instance Package PromisedComponent where
@@ -47,13 +48,14 @@ data PreExistingComponent = PreExistingComponent
   , pc_cid :: ComponentId
   , pc_open_uid :: OpenUnitId
   , pc_shape :: ModuleShape
+  , pc_alias :: Maybe PrivateAlias
   }
 
 -- | Convert an 'InstalledPackageInfo' into a 'PreExistingComponent',
 -- which was brought into scope under the 'PackageName' (important for
 -- a package qualified reference.)
-ipiToPreExistingComponent :: InstalledPackageInfo -> PreExistingComponent
-ipiToPreExistingComponent ipi =
+ipiToPreExistingComponent :: Maybe PrivateAlias -> InstalledPackageInfo -> PreExistingComponent
+ipiToPreExistingComponent alias ipi =
   PreExistingComponent
     { pc_pkgname = packageName ipi
     , pc_compname = CLibName $ Installed.sourceLibName ipi
@@ -65,6 +67,7 @@ ipiToPreExistingComponent ipi =
           (Installed.installedComponentId ipi)
           (Map.fromList (Installed.instantiatedWith ipi))
     , pc_shape = shapeInstalledPackage ipi
+    , pc_alias = alias
     }
 
 instance HasMungedPackageId PreExistingComponent where
diff --git a/Cabal/src/Distribution/Backpack/UnifyM.hs b/Cabal/src/Distribution/Backpack/UnifyM.hs
index 6e0f00d9f63..b66632b5d09 100644
--- a/Cabal/src/Distribution/Backpack/UnifyM.hs
+++ b/Cabal/src/Distribution/Backpack/UnifyM.hs
@@ -481,6 +481,7 @@ convertInclude
             }
         , ci_renaming = incl@(IncludeRenaming prov_rns req_rns)
         , ci_implicit = implicit
+        , ci_alias = alias
         }
       ) = addErrContext (text "In" <+> ci_msg ci) $ do
     let pn = packageName pid
@@ -619,12 +620,31 @@ convertInclude
               | (from, to) <- rns
               ]
           return (r, prov_rns)
+
+    -- TODO: Test hiding and private depends to check that works
+
+    -- Expand the alias
+    let prepend_alias mn = case alias of
+          Just (PrivateAlias alias_mn) -> fromComponents (components alias_mn ++ components mn)
+          Nothing -> mn
+
+    let pre_prov_scope' = map (first prepend_alias) pre_prov_scope
+
+    let prov_rns'' =
+          case prov_rns' of
+            DefaultRenaming -> case alias of
+              Nothing -> DefaultRenaming
+              Just{} -> ModuleRenaming (map ((\x -> (x, prepend_alias x)) . fst) (pre_prov_scope))
+            ModuleRenaming rn -> ModuleRenaming (map (\(x, y) -> (x, prepend_alias y)) rn)
+            -- Can't happen, expanded avove
+            HidingRenaming{} -> error "unreachabel"
+
     let prov_scope =
           modSubst req_subst $
             Map.fromListWith
               (++)
               [ (k, [source v])
-              | (k, v) <- pre_prov_scope
+              | (k, v) <- pre_prov_scope'
               ]
 
     provs_u <- convertModuleProvides prov_scope
@@ -646,8 +666,9 @@ convertInclude
                     , ann_pid = pid
                     , ann_cname = compname
                     }
-              , ci_renaming = prov_rns'
+              , ci_renaming = prov_rns''
               , ci_implicit = ci_implicit ci
+              , ci_alias = alias
               }
           )
       )
diff --git a/Cabal/src/Distribution/PackageDescription/Check.hs b/Cabal/src/Distribution/PackageDescription/Check.hs
index f444a4c23fe..e8155d2b069 100644
--- a/Cabal/src/Distribution/PackageDescription/Check.hs
+++ b/Cabal/src/Distribution/PackageDescription/Check.hs
@@ -909,14 +909,15 @@ wrapParseWarning fp pw = PackageDistSuspicious (ParseWarning fp pw)
 -- each of those branch will be checked one by one.
 extractAssocDeps
   :: UnqualComponentName -- Name of the target library
-  -> CondTree ConfVar [Dependency] Library
+  -> CondTree ConfVar Dependencies Library
   -> AssocDep
 extractAssocDeps n ct =
   let a = ignoreConditions ct
    in -- Merging is fine here, remember the specific
       -- library dependencies will be checked branch
       -- by branch.
-      (n, snd a)
+      -- MP: TOOD: WRONG
+      (n, publicDependencies (snd a))
 
 -- | August 2022: this function is an oddity due to the historical
 -- GenericPackageDescription/PackageDescription split (check
@@ -952,8 +953,8 @@ pd2gpd pd = gpd
         }
 
     -- From target to simple, unconditional CondTree.
-    t2c :: a -> CondTree ConfVar [Dependency] a
-    t2c a = CondNode a [] []
+    t2c :: a -> CondTree ConfVar Dependencies a
+    t2c a = CondNode a mempty []
 
     -- From named target to unconditional CondTree. Notice we have
     -- a function to extract the name *and* a function to modify
@@ -963,7 +964,7 @@ pd2gpd pd = gpd
       :: (a -> UnqualComponentName)
       -> (a -> a)
       -> a
-      -> (UnqualComponentName, CondTree ConfVar [Dependency] a)
+      -> (UnqualComponentName, CondTree ConfVar Dependencies a)
     t2cName nf mf a = (nf a, t2c . mf $ a)
 
     ln :: Library -> UnqualComponentName
diff --git a/Cabal/src/Distribution/PackageDescription/Check/Conditional.hs b/Cabal/src/Distribution/PackageDescription/Check/Conditional.hs
index da05b2c80b9..60ffd13477a 100644
--- a/Cabal/src/Distribution/PackageDescription/Check/Conditional.hs
+++ b/Cabal/src/Distribution/PackageDescription/Check/Conditional.hs
@@ -61,8 +61,8 @@ annotateCondTree
    . (Eq a, Monoid a)
   => [PackageFlag] -- User flags.
   -> TargetAnnotation a
-  -> CondTree ConfVar [Dependency] a
-  -> CondTree ConfVar [Dependency] (TargetAnnotation a)
+  -> CondTree ConfVar Dependencies a
+  -> CondTree ConfVar Dependencies (TargetAnnotation a)
 annotateCondTree fs ta (CondNode a c bs) =
   let ta' = updateTargetAnnotation a ta
       bs' = map (annotateBranch ta') bs
@@ -71,10 +71,10 @@ annotateCondTree fs ta (CondNode a c bs) =
   where
     annotateBranch
       :: TargetAnnotation a
-      -> CondBranch ConfVar [Dependency] a
+      -> CondBranch ConfVar Dependencies a
       -> CondBranch
           ConfVar
-          [Dependency]
+          Dependencies
           (TargetAnnotation a)
     annotateBranch wta (CondBranch k t mf) =
       let uf = isPkgFlagCond k
@@ -117,13 +117,13 @@ crossAnnotateBranches
   :: forall a
    . (Eq a, Monoid a)
   => [PackageFlag] -- `default: true` flags.
-  -> [CondBranch ConfVar [Dependency] (TargetAnnotation a)]
-  -> [CondBranch ConfVar [Dependency] (TargetAnnotation a)]
+  -> [CondBranch ConfVar Dependencies (TargetAnnotation a)]
+  -> [CondBranch ConfVar Dependencies (TargetAnnotation a)]
 crossAnnotateBranches fs bs = map crossAnnBranch bs
   where
     crossAnnBranch
-      :: CondBranch ConfVar [Dependency] (TargetAnnotation a)
-      -> CondBranch ConfVar [Dependency] (TargetAnnotation a)
+      :: CondBranch ConfVar Dependencies (TargetAnnotation a)
+      -> CondBranch ConfVar Dependencies (TargetAnnotation a)
     crossAnnBranch wr =
       let
         rs = filter (/= wr) bs
@@ -131,7 +131,7 @@ crossAnnotateBranches fs bs = map crossAnnBranch bs
        in
         updateTargetAnnBranch (mconcat ts) wr
 
-    realiseBranch :: CondBranch ConfVar [Dependency] (TargetAnnotation a) -> Maybe a
+    realiseBranch :: CondBranch ConfVar Dependencies (TargetAnnotation a) -> Maybe a
     realiseBranch b =
       let
         -- We are only interested in True by default package flags.
@@ -144,8 +144,8 @@ crossAnnotateBranches fs bs = map crossAnnBranch bs
 
     updateTargetAnnBranch
       :: a
-      -> CondBranch ConfVar [Dependency] (TargetAnnotation a)
-      -> CondBranch ConfVar [Dependency] (TargetAnnotation a)
+      -> CondBranch ConfVar Dependencies (TargetAnnotation a)
+      -> CondBranch ConfVar Dependencies (TargetAnnotation a)
     updateTargetAnnBranch a (CondBranch k t mt) =
       let updateTargetAnnTree (CondNode ka c wbs) =
             (CondNode (updateTargetAnnotation a ka) c wbs)
@@ -163,7 +163,7 @@ checkCondTarget
   -- Naming function (some targets
   -- need to have their name
   -- spoonfed to them.
-  -> (UnqualComponentName, CondTree ConfVar [Dependency] a)
+  -> (UnqualComponentName, CondTree ConfVar Dependencies a)
   -- Target name/condtree.
   -> CheckM m ()
 checkCondTarget fs cf nf (unqualName, ct) =
@@ -172,7 +172,7 @@ checkCondTarget fs cf nf (unqualName, ct) =
     -- Walking the tree. Remember that CondTree is not a binary
     -- tree but a /rose/tree.
     wTree
-      :: CondTree ConfVar [Dependency] (TargetAnnotation a)
+      :: CondTree ConfVar Dependencies (TargetAnnotation a)
       -> CheckM m ()
     wTree (CondNode ta _ bs)
       -- There are no branches ([] == True) *or* every branch
@@ -190,13 +190,13 @@ checkCondTarget fs cf nf (unqualName, ct) =
           mapM_ wBranch bs
 
     isSimple
-      :: CondBranch ConfVar [Dependency] (TargetAnnotation a)
+      :: CondBranch ConfVar Dependencies (TargetAnnotation a)
       -> Bool
     isSimple (CondBranch _ _ Nothing) = True
     isSimple (CondBranch _ _ (Just _)) = False
 
     wBranch
-      :: CondBranch ConfVar [Dependency] (TargetAnnotation a)
+      :: CondBranch ConfVar Dependencies (TargetAnnotation a)
       -> CheckM m ()
     wBranch (CondBranch k t mf) = do
       checkCondVars k
diff --git a/Cabal/src/Distribution/Simple/Configure.hs b/Cabal/src/Distribution/Simple/Configure.hs
index 0a788af830c..0d11f65c4f4 100644
--- a/Cabal/src/Distribution/Simple/Configure.hs
+++ b/Cabal/src/Distribution/Simple/Configure.hs
@@ -723,9 +723,9 @@ computeLocalBuildConfig cfg comp programDb = do
 
 data PackageInfo = PackageInfo
   { internalPackageSet :: Set LibraryName
-  , promisedDepsSet :: Map (PackageName, ComponentName) ComponentId
+  , promisedDepsSet :: Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   , installedPackageSet :: InstalledPackageIndex
-  , requiredDepsMap :: Map (PackageName, ComponentName) InstalledPackageInfo
+  , requiredDepsMap :: Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
   }
 
 configurePackage
@@ -879,7 +879,7 @@ finalizeAndConfigurePackage cfg lbc0 g_pkg_descr comp platform enabled = do
   -- that is not possible to configure a test-suite to use one
   -- version of a dependency, and the executable to use another.
   ( allConstraints :: [PackageVersionConstraint]
-    , requiredDepsMap :: Map (PackageName, ComponentName) InstalledPackageInfo
+    , requiredDepsMap :: Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
     ) <-
     either (dieWithException verbosity) return $
       combinedConstraints
@@ -1259,8 +1259,8 @@ configureComponents
 
       return lbi
 
-mkPromisedDepsSet :: [GivenComponent] -> Map (PackageName, ComponentName) ComponentId
-mkPromisedDepsSet comps = Map.fromList [((pn, CLibName ln), cid) | GivenComponent pn ln cid <- comps]
+mkPromisedDepsSet :: [GivenComponent] -> Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
+mkPromisedDepsSet comps = Map.fromList [((pn, CLibName ln, alias), cid) | GivenComponent pn ln cid alias <- comps]
 
 -- | Adds the extra program paths from the flags provided to @configure@ as
 -- well as specified locations for certain known programs and their default
@@ -1363,10 +1363,10 @@ dependencySatisfiable
   -- ^ installed set
   -> Set LibraryName
   -- ^ library components
-  -> Map (PackageName, ComponentName) ComponentId
-  -> Map (PackageName, ComponentName) InstalledPackageInfo
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
   -- ^ required dependencies
-  -> (Dependency -> Bool)
+  -> (Maybe PrivateAlias -> Dependency -> Bool)
 dependencySatisfiable
   use_external_internal_deps
   exact_config
@@ -1376,6 +1376,7 @@ dependencySatisfiable
   packageLibraries
   promisedDeps
   requiredDepsMap
+  alias
   (Dependency depName vr sublibs)
     | exact_config =
         -- When we're given '--exact-configuration', we assume that all
@@ -1398,6 +1399,7 @@ dependencySatisfiable
                   , CLibName $
                       LSubLibName $
                         packageNameToUnqualComponentName depName
+                  , alias
                   )
                   requiredDepsMap
             )
@@ -1447,8 +1449,8 @@ dependencySatisfiable
           -- Don't check if it's visible, we promise to build it before we need it.
           || promised
         where
-          maybeIPI = Map.lookup (depName, CLibName lib) requiredDepsMap
-          promised = isJust $ Map.lookup (depName, CLibName lib) promisedDeps
+          maybeIPI = Map.lookup (depName, CLibName lib, alias) requiredDepsMap
+          promised = isJust $ Map.lookup (depName, CLibName lib, alias) promisedDeps
 
 -- | Finalize a generic package description.
 --
@@ -1458,7 +1460,7 @@ configureFinalizedPackage
   -> ConfigFlags
   -> ComponentRequestedSpec
   -> [PackageVersionConstraint]
-  -> (Dependency -> Bool)
+  -> (Maybe PrivateAlias -> Dependency -> Bool)
   -- ^ tests if a dependency is satisfiable.
   -- Might say it's satisfiable even when not.
   -> Compiler
@@ -1525,10 +1527,10 @@ configureDependencies
   :: Verbosity
   -> UseExternalInternalDeps
   -> Set LibraryName
-  -> Map (PackageName, ComponentName) ComponentId
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   -> InstalledPackageIndex
   -- ^ installed packages
-  -> Map (PackageName, ComponentName) InstalledPackageInfo
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
   -- ^ required deps
   -> PackageDescription
   -> ComponentRequestedSpec
@@ -1548,7 +1550,7 @@ configureDependencies
           partitionEithers $
             concat
               [ fmap (\s -> (dep, s)) <$> status
-              | dep <- enabledBuildDepends pkg_descr enableSpec
+              | (alias, dep) <- enabledBuildDepends pkg_descr enableSpec
               , let status =
                       selectDependency
                         (package pkg_descr)
@@ -1557,6 +1559,7 @@ configureDependencies
                         installedPackageSet
                         requiredDepsMap
                         use_external_internal_deps
+                        alias
                         dep
               ]
 
@@ -1779,16 +1782,17 @@ selectDependency
   -- ^ Package id of current package
   -> Set LibraryName
   -- ^ package libraries
-  -> Map (PackageName, ComponentName) ComponentId
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   -- ^ Set of components that are promised, i.e. are not installed already. See 'PromisedDependency' for more details.
   -> InstalledPackageIndex
   -- ^ Installed packages
-  -> Map (PackageName, ComponentName) InstalledPackageInfo
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
   -- ^ Packages for which we have been given specific deps to
   -- use
   -> UseExternalInternalDeps
   -- ^ Are we configuring a
   -- single component?
+  -> Maybe PrivateAlias
   -> Dependency
   -> [Either FailedDependency DependencyResolution]
 selectDependency
@@ -1798,6 +1802,7 @@ selectDependency
   installedIndex
   requiredDepsMap
   use_external_internal_deps
+  alias
   (Dependency dep_pkgname vr libs) =
     -- If the dependency specification matches anything in the internal package
     -- index, then we prefer that match to anything in the second.
@@ -1831,31 +1836,31 @@ selectDependency
       -- We have to look it up externally
       do_external_external :: LibraryName -> Either FailedDependency DependencyResolution
       do_external_external lib
-        | Just cid <- Map.lookup (dep_pkgname, CLibName lib) promisedIndex =
-            return $ PromisedDependency (PromisedComponent dep_pkgname (AnnotatedId currentCabalId (CLibName lib) cid))
+        | Just cid <- Map.lookup (dep_pkgname, CLibName lib, alias) promisedIndex =
+            return $ PromisedDependency (PromisedComponent dep_pkgname (AnnotatedId currentCabalId (CLibName lib) cid) alias)
       do_external_external lib = do
-        ipi <- case Map.lookup (dep_pkgname, CLibName lib) requiredDepsMap of
+        ipi <- case Map.lookup (dep_pkgname, CLibName lib, alias) requiredDepsMap of
           -- If we know the exact pkg to use, then use it.
           Just pkginstance -> Right pkginstance
           -- Otherwise we just pick an arbitrary instance of the latest version.
           Nothing -> case pickLastIPI $ PackageIndex.lookupInternalDependency installedIndex dep_pkgname vr lib of
             Nothing -> Left (DependencyNotExists dep_pkgname)
             Just pkg -> Right pkg
-        return $ ExternalDependency $ ipiToPreExistingComponent ipi
+        return $ ExternalDependency $ ipiToPreExistingComponent alias ipi
 
       do_external_internal :: LibraryName -> Either FailedDependency DependencyResolution
       do_external_internal lib
-        | Just cid <- Map.lookup (dep_pkgname, CLibName lib) promisedIndex =
-            return $ PromisedDependency (PromisedComponent dep_pkgname (AnnotatedId currentCabalId (CLibName lib) cid))
+        | Just cid <- Map.lookup (dep_pkgname, CLibName lib, alias) promisedIndex =
+            return $ PromisedDependency (PromisedComponent dep_pkgname (AnnotatedId currentCabalId (CLibName lib) cid) alias)
       do_external_internal lib = do
-        ipi <- case Map.lookup (dep_pkgname, CLibName lib) requiredDepsMap of
+        ipi <- case Map.lookup (dep_pkgname, CLibName lib, alias) requiredDepsMap of
           -- If we know the exact pkg to use, then use it.
           Just pkginstance -> Right pkginstance
           Nothing -> case pickLastIPI $ PackageIndex.lookupInternalDependency installedIndex pn vr lib of
             -- It's an internal library, being looked up externally
             Nothing -> Left (DependencyMissingInternal dep_pkgname lib)
             Just pkg -> Right pkg
-        return $ ExternalDependency $ ipiToPreExistingComponent ipi
+        return $ ExternalDependency $ ipiToPreExistingComponent alias ipi
 
       pickLastIPI :: [(Version, [InstalledPackageInfo])] -> Maybe InstalledPackageInfo
       pickLastIPI pkgs = safeHead . snd . last =<< nonEmpty pkgs
@@ -2028,7 +2033,7 @@ combinedConstraints
   -> Either
       CabalException
       ( [PackageVersionConstraint]
-      , Map (PackageName, ComponentName) InstalledPackageInfo
+      , Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
       )
 combinedConstraints constraints dependencies installedPackages = do
   when (not (null badComponentIds)) $
@@ -2043,23 +2048,23 @@ combinedConstraints constraints dependencies installedPackages = do
     allConstraints =
       constraints
         ++ [ thisPackageVersionConstraint (packageId pkg)
-           | (_, _, _, Just pkg) <- dependenciesPkgInfo
+           | (_, _, _, _, Just pkg) <- dependenciesPkgInfo
            ]
 
-    idConstraintMap :: Map (PackageName, ComponentName) InstalledPackageInfo
+    idConstraintMap :: Map (PackageName, ComponentName, Maybe PrivateAlias) InstalledPackageInfo
     idConstraintMap =
       Map.fromList
         -- NB: do NOT use the packageName from
         -- dependenciesPkgInfo!
-        [ ((pn, cname), pkg)
-        | (pn, cname, _, Just pkg) <- dependenciesPkgInfo
+        [ ((pn, cname, alias), pkg)
+        | (pn, cname, alias, _, Just pkg) <- dependenciesPkgInfo
         ]
 
     -- The dependencies along with the installed package info, if it exists
-    dependenciesPkgInfo :: [(PackageName, ComponentName, ComponentId, Maybe InstalledPackageInfo)]
+    dependenciesPkgInfo :: [(PackageName, ComponentName, Maybe PrivateAlias, ComponentId, Maybe InstalledPackageInfo)]
     dependenciesPkgInfo =
-      [ (pkgname, CLibName lname, cid, mpkg)
-      | GivenComponent pkgname lname cid <- dependencies
+      [ (pkgname, CLibName lname, alias, cid, mpkg)
+      | GivenComponent pkgname lname cid alias <- dependencies
       , let mpkg =
               PackageIndex.lookupComponentId
                 installedPackages
@@ -2070,8 +2075,8 @@ combinedConstraints constraints dependencies installedPackages = do
     -- (i.e. someone has written a hash) and didn't find it then it's
     -- an error.
     badComponentIds =
-      [ (pkgname, cname, cid)
-      | (pkgname, cname, cid, Nothing) <- dependenciesPkgInfo
+      [ (pkgname, cname, alias, cid)
+      | (pkgname, cname, alias, cid, Nothing) <- dependenciesPkgInfo
       ]
 
     dispDependencies deps =
@@ -2085,8 +2090,9 @@ combinedConstraints constraints dependencies installedPackages = do
                   _ -> ":" <<>> pretty cname
                 <<>> char '='
                 <<>> pretty cid
+                <<>> maybe "" (\a -> "=" <<>> pretty a) alias
             )
-        | (pkgname, cname, cid) <- deps
+        | (pkgname, cname, alias, cid) <- deps
         ]
 
 -- -----------------------------------------------------------------------------
diff --git a/Cabal/src/Distribution/Simple/Errors.hs b/Cabal/src/Distribution/Simple/Errors.hs
index 1ca8c97c6c6..68f30231591 100644
--- a/Cabal/src/Distribution/Simple/Errors.hs
+++ b/Cabal/src/Distribution/Simple/Errors.hs
@@ -126,7 +126,7 @@ data CabalException
   | CantFindForeignLibraries [String]
   | ExpectedAbsoluteDirectory FilePath
   | FlagsNotSpecified [FlagName]
-  | EncounteredMissingDependency [Dependency]
+  | EncounteredMissingDependency Dependencies
   | CompilerDoesn'tSupportThinning
   | CompilerDoesn'tSupportReexports
   | CompilerDoesn'tSupportBackpack
@@ -551,8 +551,11 @@ exceptionMessage e = case e of
             . sep
             . punctuate comma
             . map (pretty . simplifyDependency)
+            . allDependencies
             $ missing
          )
+    where
+      allDependencies (Dependencies pub priv) = pub ++ concatMap private_depends priv
   CompilerDoesn'tSupportThinning ->
     "Your compiler does not support thinning and renaming on "
       ++ "package flags.  To use this feature you must use "
diff --git a/Cabal/src/Distribution/Simple/GHC/Internal.hs b/Cabal/src/Distribution/Simple/GHC/Internal.hs
index a4b75cdb6d3..108bba30250 100644
--- a/Cabal/src/Distribution/Simple/GHC/Internal.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Internal.hs
@@ -672,7 +672,7 @@ getHaskellObjects _implInfo lib lbi clbi pref wanted_obj_ext allow_split_objs
 -- and is a hack to avoid passing bogus `-package` arguments to GHC. The assumption being that
 -- in 99% of cases we will include the right `-package` so that the C file finds the right headers.
 mkGhcOptPackages
-  :: Map (PackageName, ComponentName) ComponentId
+  :: Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   -> ComponentLocalBuildInfo
   -> [(OpenUnitId, ModuleRenaming)]
 mkGhcOptPackages promisedPkgsMap clbi =
diff --git a/Cabal/src/Distribution/Simple/Setup.hs b/Cabal/src/Distribution/Simple/Setup.hs
index 861cf16095c..7a9834195e7 100644
--- a/Cabal/src/Distribution/Simple/Setup.hs
+++ b/Cabal/src/Distribution/Simple/Setup.hs
@@ -44,6 +44,7 @@ module Distribution.Simple.Setup
   , ConfigFlags (..)
   , emptyConfigFlags
   , defaultConfigFlags
+  , AliasDependency (..)
   , configureCommand
   , configPrograms
   , readPackageDb
diff --git a/Cabal/src/Distribution/Simple/Setup/Config.hs b/Cabal/src/Distribution/Simple/Setup/Config.hs
index 14e76c7d769..dfa388a60b7 100644
--- a/Cabal/src/Distribution/Simple/Setup/Config.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Config.hs
@@ -41,6 +41,8 @@ module Distribution.Simple.Setup.Config
   , configureArgs
   , configureOptions
   , installDirsOptions
+  -- TODO: Move
+  , AliasDependency (..)
   ) where
 
 import Distribution.Compat.Prelude hiding (get)
@@ -258,6 +260,11 @@ pattern ConfigCommonFlags
 instance Binary ConfigFlags
 instance Structured ConfigFlags
 
+data AliasDependency = AliasDependency PrivateAlias GivenComponent deriving (Generic, Read, Show, Typeable)
+
+instance Binary AliasDependency
+instance Structured AliasDependency
+
 -- | More convenient version of 'configPrograms'. Results in an
 -- 'error' if internal invariant is violated.
 configPrograms :: WithCallStack (ConfigFlags -> ProgramDb)
@@ -756,7 +763,7 @@ configureOptions showOrParseArgs =
           configDependencies
           (\v flags -> flags{configDependencies = v})
           ( reqArg
-              "NAME[:COMPONENT_NAME]=CID"
+              "NAME[:COMPONENT_NAME]=CID[=ALIAS]"
               (parsecToReadE (const "dependency expected") ((\x -> [x]) `fmap` parsecGivenComponent))
               (map prettyGivenComponent)
           )
@@ -767,7 +774,7 @@ configureOptions showOrParseArgs =
           configPromisedDependencies
           (\v flags -> flags{configPromisedDependencies = v})
           ( reqArg
-              "NAME[:COMPONENT_NAME]=CID"
+              "NAME[:COMPONENT_NAME]=CID[=ALIAS]"
               (parsecToReadE (const "dependency expected") ((\x -> [x]) `fmap` parsecGivenComponent))
               (map prettyGivenComponent)
           )
@@ -898,6 +905,19 @@ showProfDetailLevelFlag :: Flag ProfDetailLevel -> [String]
 showProfDetailLevelFlag NoFlag = []
 showProfDetailLevelFlag (Flag dl) = [showProfDetailLevel dl]
 
+_parsecAliasDependency :: ParsecParser AliasDependency
+_parsecAliasDependency = do
+  pn <- parsec
+  _ <- P.char '='
+  gc <- parsecGivenComponent
+  return $ AliasDependency pn gc
+
+_prettyAliasDependency :: AliasDependency -> String
+_prettyAliasDependency (AliasDependency pn gc) =
+  prettyShow pn
+    ++ "="
+    ++ prettyGivenComponent gc
+
 parsecGivenComponent :: ParsecParser GivenComponent
 parsecGivenComponent = do
   pn <- parsec
@@ -910,16 +930,20 @@ parsecGivenComponent = do
         else LSubLibName ucn
   _ <- P.char '='
   cid <- parsec
-  return $ GivenComponent pn ln cid
+  alias <- P.option Nothing $ do
+    _ <- P.char '='
+    Just <$> parsec
+  return $ GivenComponent pn ln cid alias
 
 prettyGivenComponent :: GivenComponent -> String
-prettyGivenComponent (GivenComponent pn cn cid) =
+prettyGivenComponent (GivenComponent pn cn cid alias) =
   prettyShow pn
     ++ case cn of
       LMainLibName -> ""
       LSubLibName n -> ":" ++ prettyShow n
     ++ "="
     ++ prettyShow cid
+    ++ maybe "" (\a -> "=" ++ prettyShow a) alias
 
 installDirsOptions :: [OptionField (InstallDirs (Flag PathTemplate))]
 installDirsOptions =
diff --git a/Cabal/src/Distribution/Types/ComponentInclude.hs b/Cabal/src/Distribution/Types/ComponentInclude.hs
index 6999b6544d7..e2e4057a042 100644
--- a/Cabal/src/Distribution/Types/ComponentInclude.hs
+++ b/Cabal/src/Distribution/Types/ComponentInclude.hs
@@ -7,6 +7,7 @@ module Distribution.Types.ComponentInclude
 
 import Distribution.Types.AnnotatedId
 import Distribution.Types.ComponentName
+import Distribution.Types.Dependency (PrivateAlias)
 import Distribution.Types.PackageId
 
 -- Once ci_id is refined to an 'OpenUnitId' or 'DefUnitId',
@@ -19,7 +20,9 @@ data ComponentInclude id rn = ComponentInclude
   , ci_implicit :: Bool
   -- ^ Did this come from an entry in @mixins@, or
   -- was implicitly generated by @build-depends@?
+  , ci_alias :: Maybe PrivateAlias
   }
+  deriving (Show)
 
 ci_id :: ComponentInclude id rn -> id
 ci_id = ann_id . ci_ann_id
diff --git a/Cabal/src/Distribution/Types/ComponentLocalBuildInfo.hs b/Cabal/src/Distribution/Types/ComponentLocalBuildInfo.hs
index 0728656620e..8af914467c8 100644
--- a/Cabal/src/Distribution/Types/ComponentLocalBuildInfo.hs
+++ b/Cabal/src/Distribution/Types/ComponentLocalBuildInfo.hs
@@ -41,7 +41,7 @@ data ComponentLocalBuildInfo
       , componentIsIndefinite_ :: Bool
       -- ^ Is this an indefinite component (i.e. has unfilled holes)?
       , componentInstantiatedWith :: [(ModuleName, OpenModule)]
-      -- ^ How the component was instantiated
+      -- ^ How the component was instantiate
       , componentPackageDeps :: [(UnitId, MungedPackageId)]
       -- ^ Resolved internal and external package dependencies for this component.
       -- The 'BuildInfo' specifies a set of build dependencies that must be
diff --git a/Cabal/src/Distribution/Types/GivenComponent.hs b/Cabal/src/Distribution/Types/GivenComponent.hs
index c8314311d89..eaab3e8e713 100644
--- a/Cabal/src/Distribution/Types/GivenComponent.hs
+++ b/Cabal/src/Distribution/Types/GivenComponent.hs
@@ -8,6 +8,7 @@ module Distribution.Types.GivenComponent
 import Distribution.Compat.Prelude
 
 import Distribution.Types.ComponentId
+import Distribution.Types.Dependency
 import Distribution.Types.LibraryName
 import Distribution.Types.PackageName
 
@@ -22,6 +23,7 @@ data GivenComponent = GivenComponent
   , givenComponentName :: LibraryName -- --dependency is for libraries
   -- only, not for any component
   , givenComponentId :: ComponentId
+  , givenComponentAlias :: Maybe PrivateAlias
   }
   deriving (Generic, Read, Show, Eq, Typeable)
 
diff --git a/Cabal/src/Distribution/Types/LocalBuildConfig.hs b/Cabal/src/Distribution/Types/LocalBuildConfig.hs
index 9126d92f1eb..4fd700d83e4 100644
--- a/Cabal/src/Distribution/Types/LocalBuildConfig.hs
+++ b/Cabal/src/Distribution/Types/LocalBuildConfig.hs
@@ -101,7 +101,7 @@ data ComponentBuildDescr = ComponentBuildDescr
   -- ^ A map from component name to all matching
   -- components.  These coincide with 'componentGraph'
   -- There may be more than one matching component because of backpack instantiations
-  , promisedPkgs :: Map (PackageName, ComponentName) ComponentId
+  , promisedPkgs :: Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   -- ^ The packages we were promised, but aren't already installed.
   -- MP: Perhaps this just needs to be a Set UnitId at this stage.
   , installedPkgs :: InstalledPackageIndex
diff --git a/Cabal/src/Distribution/Types/LocalBuildInfo.hs b/Cabal/src/Distribution/Types/LocalBuildInfo.hs
index a5706fff09a..e0e3d58da79 100644
--- a/Cabal/src/Distribution/Types/LocalBuildInfo.hs
+++ b/Cabal/src/Distribution/Types/LocalBuildInfo.hs
@@ -156,7 +156,7 @@ pattern LocalBuildInfo
   -> Maybe (SymbolicPath Pkg File)
   -> Graph ComponentLocalBuildInfo
   -> Map ComponentName [ComponentLocalBuildInfo]
-  -> Map (PackageName, ComponentName) ComponentId
+  -> Map (PackageName, ComponentName, Maybe PrivateAlias) ComponentId
   -> InstalledPackageIndex
   -> PackageDescription
   -> ProgramDb
diff --git a/cabal-install-solver/cabal-install-solver.cabal b/cabal-install-solver/cabal-install-solver.cabal
index e692c79ce88..ba0e8c165c6 100644
--- a/cabal-install-solver/cabal-install-solver.cabal
+++ b/cabal-install-solver/cabal-install-solver.cabal
@@ -69,6 +69,7 @@ library
     Distribution.Solver.Modular.MessageUtils
     Distribution.Solver.Modular.Package
     Distribution.Solver.Modular.Preference
+    Distribution.Solver.Modular.PrivateScopeClosure
     Distribution.Solver.Modular.PSQ
     Distribution.Solver.Modular.RetryLog
     Distribution.Solver.Modular.Solver
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Builder.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Builder.hs
index 5d196f4fd9f..95373cbd473 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Builder.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Builder.hs
@@ -73,7 +73,7 @@ extendOpen qpn' gs s@(BS { rdeps = gs', open = o' }) = go gs' o' gs
       -- the later addition will have better dependency information.
     go g o ((Stanza sn@(SN qpn _) t)           : ngs) =
         go g (StanzaGoal sn t (flagGR qpn) : o) ngs
-    go g o ((Simple (LDep dr (Dep (PkgComponent qpn _) _)) c) : ngs)
+    go g o ((Simple (LDep dr (Dep (PkgComponent qpn _) _is_private _)) c) : ngs)
       | qpn == qpn'       =
             -- We currently only add a self-dependency to the graph if it is
             -- between a package and its setup script. The edge creates a cycle
@@ -100,12 +100,12 @@ extendOpen qpn' gs s@(BS { rdeps = gs', open = o' }) = go gs' o' gs
 
 -- | Given the current scope, qualify all the package names in the given set of
 -- dependencies and then extend the set of open goals accordingly.
-scopedExtendOpen :: QPN -> FlaggedDeps PN -> FlagInfo ->
+scopedExtendOpen :: RevDepMap -> QPN -> FlaggedDeps PN -> FlagInfo ->
                     BuildState -> BuildState
-scopedExtendOpen qpn fdeps fdefs s = extendOpen qpn gs s
+scopedExtendOpen rdm qpn fdeps fdefs s = extendOpen qpn gs s
   where
     -- Qualify all package names
-    qfdeps = qualifyDeps (qualifyOptions s) qpn fdeps
+    qfdeps = qualifyDeps (qualifyOptions s) rdm qpn fdeps
     -- Introduce all package flags
     qfdefs = L.map (\ (fn, b) -> Flagged (FN qpn fn) b [] []) $ M.toList fdefs
     -- Combine new package and flag goals
@@ -179,8 +179,8 @@ addChildren bs@(BS { rdeps = rdm, next = OneGoal (StanzaGoal qsn@(SN qpn _) t gr
 -- and furthermore we update the set of goals.
 --
 -- TODO: We could inline this above.
-addChildren bs@(BS { next = Instance qpn (PInfo fdeps _ fdefs _) }) =
-  addChildren ((scopedExtendOpen qpn fdeps fdefs bs)
+addChildren bs@(BS { rdeps = rdm, next = Instance qpn (PInfo fdeps _ fdefs _) }) =
+  addChildren ((scopedExtendOpen rdm qpn fdeps fdefs bs)
          { next = Goals })
 
 {-------------------------------------------------------------------------------
@@ -263,7 +263,7 @@ buildTree idx (IndependentGoals ind) igs =
     topLevelGoal qpn = PkgGoal qpn UserGoal
 
     qpns | ind       = L.map makeIndependent igs
-         | otherwise = L.map (Q (PackagePath DefaultNamespace QualToplevel)) igs
+         | otherwise = L.map (Q (PackagePath DefaultNamespace QualToplevel) ) igs
 
 {-------------------------------------------------------------------------------
   Goals
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/ConfiguredConversion.hs b/cabal-install-solver/src/Distribution/Solver/Modular/ConfiguredConversion.hs
index 0e2e8ad5baa..86928083faf 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/ConfiguredConversion.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/ConfiguredConversion.hs
@@ -4,9 +4,8 @@ module Distribution.Solver.Modular.ConfiguredConversion
 
 import Data.Maybe
 import Prelude hiding (pi)
-import Data.Either (partitionEithers)
 
-import Distribution.Package (UnitId, packageId)
+import Distribution.Package (UnitId)
 
 import qualified Distribution.Simple.PackageIndex as SI
 
@@ -21,6 +20,7 @@ import           Distribution.Solver.Types.SolverId
 import           Distribution.Solver.Types.SolverPackage
 import           Distribution.Solver.Types.InstSolverPackage
 import           Distribution.Solver.Types.SourcePackage
+import Distribution.Types.Dependency (PrivateAlias)
 
 -- | Converts from the solver specific result @CP QPN@ into
 -- a 'ResolverPackage', which can then be converted into
@@ -33,40 +33,69 @@ convCP iidx sidx (CP qpi fa es ds) =
     Left  pi -> PreExisting $
                   InstSolverPackage {
                     instSolverPkgIPI = fromJust $ SI.lookupUnitId iidx pi,
-                    instSolverPkgLibDeps = fmap fst ds',
-                    instSolverPkgExeDeps = fmap snd ds'
+                    instSolverPkgLibDeps  = fmap fst (ds' Nothing),
+                    instSolverPkgExeDeps  = fmap snd (ds' Nothing)
                   }
     Right pi -> Configured $
-                  SolverPackage {
+                  let libAndExeDeps = ds' (Just (pkgName pi))
+                   in SolverPackage {
                       solverPkgSource = srcpkg,
                       solverPkgFlags = fa,
                       solverPkgStanzas = es,
-                      solverPkgLibDeps = fmap fst ds',
-                      solverPkgExeDeps = fmap snd ds'
+                      solverPkgLibDeps = fmap fst libAndExeDeps,
+                      solverPkgExeDeps = fmap snd libAndExeDeps
                     }
       where
         srcpkg = fromMaybe (error "convCP: lookupPackageId failed") $ CI.lookupPackageId sidx pi
   where
-    ds' :: ComponentDeps ([SolverId] {- lib -}, [SolverId] {- exe -})
-    ds' = fmap (partitionEithers . map convConfId) ds
+
+    ds' :: Maybe PackageName -> ComponentDeps (([(SolverId, Maybe PrivateAlias)] {- lib -}, [SolverId] {- exe -}))
+    ds' pn = fmap (partitionDeps . map (convConfId pn)) ds
+
+partitionDeps :: [Converted] -> (([(SolverId, Maybe PrivateAlias)], [SolverId]))
+partitionDeps [] = ([], [])
+partitionDeps (dep:deps) =
+  let (p, e) = partitionDeps deps
+  in case dep of
+        AliasPkg sid pn -> ((sid, Just pn) : p, e)
+        NormalPkg sid -> ((sid, Nothing) :p, e)
+        NormalExe sid -> (p, sid:e)
 
 convPI :: PI QPN -> Either UnitId PackageId
 convPI (PI _ (I _ (Inst pi))) = Left pi
-convPI pi                     = Right (packageId (either id id (convConfId pi)))
+convPI (PI (Q _ pn) (I v _)) = Right (PackageIdentifier pn v)
+
+data Converted = NormalPkg SolverId | NormalExe SolverId | AliasPkg SolverId PrivateAlias
+  deriving Show
 
-convConfId :: PI QPN -> Either SolverId {- is lib -} SolverId {- is exe -}
-convConfId (PI (Q (PackagePath _ q) pn) (I v loc)) =
+convConfId :: Maybe PackageName -> PI QPN -> Converted
+convConfId parent (PI (Q (PackagePath ns qn) pn) (I v loc)) =
     case loc of
-        Inst pi -> Left (PreExistingId sourceId pi)
+        Inst pi
+          -- As below, we need to identify where `AliasPkg` applies. This is
+          -- needed to qualify `solverPkgLibDeps` since we may have multiple
+          -- instances of the same package qualified.
+          | QualAlias pn' _ alias <- qn
+          , parent == Just pn' -> AliasPkg (PreExistingId sourceId pi) alias
+
+          | otherwise
+          -> NormalPkg (PreExistingId sourceId pi)
         _otherwise
-          | QualExe _ pn' <- q
+          -- Same reasoning as for exes, the "top" qualified goal is the one
+          -- which is private and needs to be aliased, but there might be other goals underneath which
+          -- are solved in the same scope (but are not private)
+          | QualAlias pn' _ alias <- qn
+          , parent == Just pn' -> AliasPkg (PlannedId sourceId) alias
+
+          | IndependentBuildTool _ pn' <- ns
           -- NB: the dependencies of the executable are also
           -- qualified.  So the way to tell if this is an executable
           -- dependency is to make sure the qualifier is pointing
           -- at the actual thing.  Fortunately for us, I was
           -- silly and didn't allow arbitrarily nested build-tools
           -- dependencies, so a shallow check works.
-          , pn == pn' -> Right (PlannedId sourceId)
-          | otherwise    -> Left  (PlannedId sourceId)
+          , pn == pn' -> NormalExe (PlannedId sourceId)
+
+          | otherwise    -> NormalPkg  (PlannedId sourceId)
   where
     sourceId    = PackageIdentifier pn v
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/ConflictSet.hs b/cabal-install-solver/src/Distribution/Solver/Modular/ConflictSet.hs
index 00cf15b466f..6c9b4280986 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/ConflictSet.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/ConflictSet.hs
@@ -74,6 +74,15 @@ data Conflict =
     -- means that package y's constraint 'x >= 2.0' excluded some version of x.
   | VersionConflict QPN OrderedVersionRange
 
+    -- | The conflict set variable represents a package that was excluded for
+    -- violating the closure property of a private-scope, because that package is part of
+    -- the closure of the private scope, but it itself is not
+    -- included in it. For example, the conflict set entry '(P pkgC,
+    -- PrivateScopeClosureConflict pkgA:lib:G0:pkgB pkgA:lib:G0:pkgD)' means
+    -- that pkgC is in the (private-deps) closure from pkgA:lib:G0:pkgB to
+    -- pkgA:lib:G0:pkgD, but pkgC is not included in the private scope pkgA:lib:G0.
+  | PrivateScopeClosureConflict QPN QPN
+
     -- | Any other conflict.
   | OtherConflict
   deriving (Eq, Ord, Show)
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Dependency.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Dependency.hs
index 27debc9c6f0..32076b38897 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Dependency.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Dependency.hs
@@ -58,6 +58,7 @@ import Distribution.Solver.Types.PackagePath
 import Distribution.Types.LibraryName
 import Distribution.Types.PkgconfigVersionRange
 import Distribution.Types.UnqualComponentName
+import Distribution.Types.Dependency
 
 {-------------------------------------------------------------------------------
   Constrained instances
@@ -92,7 +93,7 @@ data FlaggedDep qpn =
     -- (e.g., a test suite or benchmark) is enabled.
   | Stanza  (SN qpn)       (TrueFlaggedDeps qpn)
     -- | Dependencies which are always enabled, for the component 'comp'.
-  | Simple (LDep qpn) Component
+  | Simple (LDep qpn) Component deriving Show
 
 -- | Conservatively flatten out flagged dependencies
 --
@@ -114,16 +115,16 @@ type FalseFlaggedDeps qpn = FlaggedDeps qpn
 -- is used both to record the dependencies as well as who's doing the
 -- depending; having a 'Functor' instance makes bugs where we don't distinguish
 -- these two far too likely. (By rights 'LDep' ought to have two type variables.)
-data LDep qpn = LDep (DependencyReason qpn) (Dep qpn)
+data LDep qpn = LDep (DependencyReason qpn) (Dep qpn) deriving Show
 
 -- | A dependency (constraint) associates a package name with a constrained
 -- instance. It can also represent other types of dependencies, such as
 -- dependencies on language extensions.
-data Dep qpn = Dep (PkgComponent qpn) CI  -- ^ dependency on a package component
+data Dep qpn = Dep (PkgComponent qpn) IsPrivate CI  -- ^ dependency on a package component
              | Ext Extension              -- ^ dependency on a language extension
              | Lang Language              -- ^ dependency on a language version
              | Pkg PkgconfigName PkgconfigVersionRange  -- ^ dependency on a pkg-config package
-  deriving Functor
+  deriving (Show, Functor)
 
 -- | An exposed component within a package. This type is used to represent
 -- build-depends and build-tool-depends dependencies.
@@ -174,15 +175,15 @@ data QualifyOptions = QO {
 --
 -- NOTE: It's the _dependencies_ of a package that may or may not be independent
 -- from the package itself. Package flag choices must of course be consistent.
-qualifyDeps :: QualifyOptions -> QPN -> FlaggedDeps PN -> FlaggedDeps QPN
-qualifyDeps QO{..} (Q pp@(PackagePath ns q) pn) = go
+qualifyDeps :: QualifyOptions -> RevDepMap -> QPN -> FlaggedDeps PN -> FlaggedDeps QPN
+qualifyDeps QO{..} rdm (Q pp@(PackagePath ns q) pn) = go
   where
     go :: FlaggedDeps PN -> FlaggedDeps QPN
     go = map go1
 
     go1 :: FlaggedDep PN -> FlaggedDep QPN
-    go1 (Flagged fn nfo t f) = Flagged (fmap (Q pp) fn) nfo (go t) (go f)
-    go1 (Stanza  sn     t)   = Stanza  (fmap (Q pp) sn)     (go t)
+    go1 (Flagged fn nfo t f) = Flagged (fmap (Q pp ) fn) nfo (go t) (go f)
+    go1 (Stanza  sn     t)   = Stanza  (fmap (Q pp ) sn)     (go t)
     go1 (Simple dep comp)    = Simple (goLDep dep comp) comp
 
     -- Suppose package B has a setup dependency on package A.
@@ -194,18 +195,19 @@ qualifyDeps QO{..} (Q pp@(PackagePath ns q) pn) = go
     -- @"A"@ into @"B-setup.A"@, but we should not apply that same qualifier
     -- to the DependencyReason.
     goLDep :: LDep PN -> Component -> LDep QPN
-    goLDep (LDep dr dep) comp = LDep (fmap (Q pp) dr) (goD dep comp)
+    goLDep (LDep dr dep) comp = LDep (fmap (Q pp ) dr) (goD dep comp)
 
     goD :: Dep PN -> Component -> Dep QPN
     goD (Ext  ext)    _    = Ext  ext
     goD (Lang lang)   _    = Lang lang
     goD (Pkg pkn vr)  _    = Pkg pkn vr
-    goD (Dep dep@(PkgComponent qpn (ExposedExe _)) ci) _ =
-        Dep (Q (PackagePath ns (QualExe pn qpn)) <$> dep) ci
-    goD (Dep dep@(PkgComponent qpn (ExposedLib _)) ci) comp
-      | qBase qpn   = Dep (Q (PackagePath ns (QualBase  pn)) <$> dep) ci
-      | qSetup comp = Dep (Q (PackagePath ns (QualSetup pn)) <$> dep) ci
-      | otherwise   = Dep (Q (PackagePath ns inheritedQ    ) <$> dep) ci
+    goD (Dep dep@(PkgComponent qpn (ExposedExe _)) is_private ci) _ =
+        Dep (Q (PackagePath (IndependentBuildTool pn qpn) QualToplevel) <$> dep) is_private ci
+    goD (Dep dep@(PkgComponent qpn (ExposedLib _)) is_private ci) comp
+      | Private pq <- is_private  = Dep (Q (PackagePath ns (QualAlias pn comp pq))  <$> dep) is_private ci
+      | qBase qpn   = Dep (Q (PackagePath ns (QualBase pn)) <$> dep) is_private ci
+      | qSetup comp = Dep (Q (PackagePath (IndependentComponent pn ComponentSetup) QualToplevel) <$> dep) is_private ci
+      | otherwise   = Dep (Q (PackagePath ns (inheritedQ qpn)    ) <$> dep) is_private ci
 
     -- If P has a setup dependency on Q, and Q has a regular dependency on R, then
     -- we say that the 'Setup' qualifier is inherited: P has an (indirect) setup
@@ -214,12 +216,19 @@ qualifyDeps QO{..} (Q pp@(PackagePath ns q) pn) = go
     -- The inherited qualifier is only used for regular dependencies; for setup
     -- and base dependencies we override the existing qualifier. See #3160 for
     -- a detailed discussion.
-    inheritedQ :: Qualifier
-    inheritedQ = case q of
-                   QualSetup _  -> q
-                   QualExe _ _  -> q
-                   QualToplevel -> q
-                   QualBase _   -> QualToplevel
+    inheritedQ :: PackageName -> Qualifier
+    inheritedQ pnx = case q of
+                   QualToplevel -> QualToplevel
+                   QualBase {}  -> QualToplevel
+                   -- check if package name is in same private scope (if so, persist)
+                   QualAlias {} ->
+                     -- Lookup this dependency in the reverse dependency map
+                     -- with the package-path of the package that introduced
+                     -- this dependency, which will match if this dependency is
+                     -- included in the same private scope.
+                     case M.lookup (Q pp pnx) rdm of
+                       Just _x -> q -- found, use same private qualifier
+                       Nothing -> QualToplevel -- not found, use top level qual
 
     -- Should we qualify this goal with the 'Base' package path?
     qBase :: PN -> Bool
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Explore.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Explore.hs
index 90038a28f5c..fe54752771d 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Explore.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Explore.hs
@@ -220,9 +220,9 @@ exploreLog mbj enableBj fineGrainedConflicts (CountConflicts countConflicts) idx
         let es' = es { esConflictMap = updateCM c (esConflictMap es) }
         in failWith (Failure c fr) (NoSolution c es')
     go (DoneF rdm a)                           = \ _   -> succeedWith Success (a, rdm)
-    go (PChoiceF qpn _ gr       ts)            =
+    go (PChoiceF qpn rdm gr       ts)            =
       backjump mbj enableBj fineGrainedConflicts
-               (couldResolveConflicts qpn)
+               (couldResolveConflicts rdm qpn)
                (logSkippedPackage qpn)
                (P qpn) (avoidSet (P qpn) gr) $ -- try children in order,
                W.mapWithKey                    -- when descending ...
@@ -267,23 +267,24 @@ exploreLog mbj enableBj fineGrainedConflicts (CountConflicts countConflicts) idx
     -- is true, because it is always safe to explore a package instance.
     -- Skipping it is an optimization. If false, it returns a new conflict set
     -- to be merged with the previous one.
-    couldResolveConflicts :: QPN -> POption -> S.Set CS.Conflict -> Maybe ConflictSet
-    couldResolveConflicts currentQPN@(Q _ pn) (POption i@(I v _) _) conflicts =
+    couldResolveConflicts :: RevDepMap -> QPN -> POption -> S.Set CS.Conflict -> Maybe ConflictSet
+    couldResolveConflicts rdm currentQPN@(Q _ pn) (POption i@(I v _) _) conflicts =
       let (PInfo deps _ _ _) = idx M.! pn M.! i
-          qdeps = qualifyDeps (defaultQualifyOptions idx) currentQPN deps
+          qdeps = qualifyDeps (defaultQualifyOptions idx) rdm currentQPN deps
 
           couldBeResolved :: CS.Conflict -> Maybe ConflictSet
           couldBeResolved CS.OtherConflict = Nothing
+          couldBeResolved (CS.PrivateScopeClosureConflict _ _) = Nothing -- Could we optimise here?
           couldBeResolved (CS.GoalConflict conflictingDep) =
               -- Check whether this package instance also has 'conflictingDep'
               -- as a dependency (ignoring flag and stanza choices).
-              if null [() | Simple (LDep _ (Dep (PkgComponent qpn _) _)) _ <- qdeps, qpn == conflictingDep]
+              if null [() | Simple (LDep _ (Dep (PkgComponent qpn _) _is_private _)) _ <- qdeps, qpn == conflictingDep]
               then Nothing
               else Just CS.empty
           couldBeResolved (CS.VersionConstraintConflict dep excludedVersion) =
               -- Check whether this package instance also excludes version
               -- 'excludedVersion' of 'dep' (ignoring flag and stanza choices).
-              let vrs = [vr | Simple (LDep _ (Dep (PkgComponent qpn _) (Constrained vr))) _ <- qdeps, qpn == dep ]
+              let vrs = [vr | Simple (LDep _ (Dep (PkgComponent qpn _) _is_private (Constrained vr))) _ <- qdeps, qpn == dep ]
                   vrIntersection = L.foldl' (.&&.) anyVersion vrs
               in if checkVR vrIntersection excludedVersion
                  then Nothing
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Index.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Index.hs
index 2f28d12de85..0c17ff731e3 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Index.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Index.hs
@@ -60,13 +60,13 @@ groupMap xs = M.fromListWith (flip (++)) (L.map (\ (x, y) -> (x, [y])) xs)
 
 defaultQualifyOptions :: Index -> QualifyOptions
 defaultQualifyOptions idx = QO {
-      qoBaseShim         = or [ dep == base
+      qoBaseShim         =  or [ dep == base
                               | -- Find all versions of base ..
                                 Just is <- [M.lookup base idx]
                                 -- .. which are installed ..
                               , (I _ver (Inst _), PInfo deps _comps _flagNfo _fr) <- M.toList is
                                 -- .. and flatten all their dependencies ..
-                              , (LDep _ (Dep (PkgComponent dep _) _ci), _comp) <- flattenFlaggedDeps deps
+                              , (LDep _ (Dep (PkgComponent dep _) _ _ci), _comp) <- flattenFlaggedDeps deps
                               ]
     , qoSetupIndependent = True
     }
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/IndexConversion.hs b/cabal-install-solver/src/Distribution/Solver/Modular/IndexConversion.hs
index 72d0b8193e3..278b8d358c9 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/IndexConversion.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/IndexConversion.hs
@@ -89,6 +89,7 @@ convId ipi = (pn, I ver $ Inst $ IPI.installedUnitId ipi)
 -- | Convert a single installed package into the solver-specific format.
 convIP :: SI.InstalledPackageIndex -> IPI.InstalledPackageInfo -> (PN, I, PInfo)
 convIP idx ipi =
+  --MP: TODO, do we need to extend package registration with private depends?
   case traverse (convIPId (DependencyReason pn M.empty S.empty) comp idx) (IPI.depends ipi) of
         Left u    -> (pn, i, PInfo [] M.empty M.empty (Just (Broken u)))
         Right fds -> (pn, i, PInfo fds components M.empty Nothing)
@@ -147,7 +148,7 @@ convIPId dr comp idx ipid =
     Nothing  -> Left ipid
     Just ipi -> let (pn, i) = convId ipi
                     name = ExposedLib LMainLibName  -- TODO: Handle sub-libraries.
-                in  Right (D.Simple (LDep dr (Dep (PkgComponent pn name) (Fixed i))) comp)
+                in  Right (D.Simple (LDep dr (Dep (PkgComponent pn name) Public (Fixed i))) comp)
                 -- NB: something we pick up from the
                 -- InstalledPackageIndex is NEVER an executable
 
@@ -172,6 +173,7 @@ convSP os arch cinfo constraints strfl solveExes (SourcePackage (PackageIdentifi
 -- want to keep the condition tree, but simplify much of the test.
 
 -- | Convert a generic package description to a solver-specific 'PInfo'.
+-- Key function for private dependencies
 convGPD :: OS -> Arch -> CompilerInfo -> [LabeledPackageConstraint]
         -> StrongFlags -> SolveExecutables -> PN -> GenericPackageDescription
         -> PInfo
@@ -182,7 +184,7 @@ convGPD os arch cinfo constraints strfl solveExes pn
 
 
     conv :: Monoid a => Component -> (a -> BuildInfo) -> DependencyReason PN ->
-            CondTree ConfVar [Dependency] a -> FlaggedDeps PN
+            CondTree ConfVar Dependencies a -> FlaggedDeps PN
     conv comp getInfo dr =
         convCondTree M.empty dr pkg os arch cinfo pn fds comp getInfo solveExes .
         addBuildableCondition getInfo
@@ -251,7 +253,7 @@ testConditionForComponent :: OS
                           -> CompilerInfo
                           -> [LabeledPackageConstraint]
                           -> (a -> Bool)
-                          -> CondTree ConfVar [Dependency] a
+                          -> CondTree ConfVar Dependencies a
                           -> Maybe Bool
 testConditionForComponent os arch cinfo constraints p tree =
     case go $ extractCondition p tree of
@@ -329,17 +331,22 @@ convCondTree :: Map FlagName Bool -> DependencyReason PN -> PackageDescription -
                 Component ->
                 (a -> BuildInfo) ->
                 SolveExecutables ->
-                CondTree ConfVar [Dependency] a -> FlaggedDeps PN
+                CondTree ConfVar Dependencies a -> FlaggedDeps PN
 convCondTree flags dr pkg os arch cinfo pn fds comp getInfo solveExes@(SolveExecutables solveExes') (CondNode info ds branches) =
              -- Merge all library and build-tool dependencies at every level in
              -- the tree of flagged dependencies. Otherwise 'extractCommon'
              -- could create duplicate dependencies, and the number of
              -- duplicates could grow exponentially from the leaves to the root
              -- of the tree.
-             mergeSimpleDeps $
-                 [ D.Simple singleDep comp
-                 | dep <- ds
-                 , singleDep <- convLibDeps dr dep ]  -- unconditional package dependencies
+             mergeSimpleDeps $ ([ D.Simple singleDep comp
+                 -- TOOD: Add scope here
+                 | dep <- publicDependencies ds
+                 , singleDep <- convLibDeps dr dep ])  -- unconditional package dependencies
+
+              ++ [ D.Simple singleDep comp
+                 -- TOOD: Add scope here
+                 | dep <- privateDependencies ds
+                 , singleDep <- convLibDepsAs dr dep ]  -- unconditional package dependencies
 
               ++ L.map (\e -> D.Simple (LDep dr (Ext  e)) comp) (allExtensions bi) -- unconditional extension dependencies
               ++ L.map (\l -> D.Simple (LDep dr (Lang l)) comp) (allLanguages  bi) -- unconditional language dependencies
@@ -390,7 +397,7 @@ mergeSimpleDeps deps = L.map (uncurry toFlaggedDep) (M.toList merged) ++ unmerge
           => (Map (SimpleFlaggedDepKey qpn) (SimpleFlaggedDepValue qpn), FlaggedDeps qpn)
           -> FlaggedDep qpn
           -> (Map (SimpleFlaggedDepKey qpn) (SimpleFlaggedDepValue qpn), FlaggedDeps qpn)
-        f (merged', unmerged') (D.Simple (LDep dr (Dep dep (Constrained vr))) comp) =
+        f (merged', unmerged') (D.Simple (LDep dr (Dep dep Public (Constrained vr))) comp) =
             ( M.insertWith mergeValues
                            (SimpleFlaggedDepKey dep comp)
                            (SimpleFlaggedDepValue dr vr)
@@ -408,7 +415,7 @@ mergeSimpleDeps deps = L.map (uncurry toFlaggedDep) (M.toList merged) ++ unmerge
                  -> SimpleFlaggedDepValue qpn
                  -> FlaggedDep qpn
     toFlaggedDep (SimpleFlaggedDepKey dep comp) (SimpleFlaggedDepValue dr vr) =
-        D.Simple (LDep dr (Dep dep (Constrained vr))) comp
+        D.Simple (LDep dr (Dep dep Public (Constrained vr))) comp
 
 -- | Branch interpreter.  Mutually recursive with 'convCondTree'.
 --
@@ -461,7 +468,7 @@ convBranch :: Map FlagName Bool
            -> Component
            -> (a -> BuildInfo)
            -> SolveExecutables
-           -> CondBranch ConfVar [Dependency] a
+           -> CondBranch ConfVar Dependencies a
            -> FlaggedDeps PN
 convBranch flags dr pkg os arch cinfo pn fds comp getInfo solveExes (CondBranch c' t' mf') =
     go c'
@@ -532,10 +539,10 @@ convBranch flags dr pkg os arch cinfo pn fds comp getInfo solveExes (CondBranch
         -- Union the DependencyReasons, because the extracted dependency can be
         -- avoided by removing the dependency from either side of the
         -- conditional.
-        [ D.Simple (LDep (unionDRs vs1 vs2) (Dep dep1 (Constrained $ vr1 .||. vr2))) comp
-        | D.Simple (LDep vs1                (Dep dep1 (Constrained vr1))) _ <- ps
-        , D.Simple (LDep vs2                (Dep dep2 (Constrained vr2))) _ <- ps'
-        , dep1 == dep2
+        [ D.Simple (LDep (unionDRs vs1 vs2) (Dep dep1 is_private1 (Constrained $ vr1 .||. vr2))) comp
+        | D.Simple (LDep vs1                (Dep dep1 is_private1 (Constrained vr1))) _ <- ps
+        , D.Simple (LDep vs2                (Dep dep2 is_private2 (Constrained vr2))) _ <- ps'
+        , dep1 == dep2 && is_private1 == is_private2
         ]
 
 -- | Merge DependencyReasons by unioning their variables.
@@ -547,12 +554,17 @@ unionDRs (DependencyReason pn' fs1 ss1) (DependencyReason _ fs2 ss2) =
 -- package) to solver-specific dependencies.
 convLibDeps :: DependencyReason PN -> Dependency -> [LDep PN]
 convLibDeps dr (Dependency pn vr libs) =
-    [ LDep dr $ Dep (PkgComponent pn (ExposedLib lib)) (Constrained vr)
+    [ LDep dr $ Dep (PkgComponent pn (ExposedLib lib)) Public (Constrained vr)
     | lib <- NonEmptySet.toList libs ]
 
+convLibDepsAs :: DependencyReason PN -> PrivateDependency -> [LDep PN]
+convLibDepsAs dr (PrivateDependency alias deps) =
+    [ LDep dr $ Dep (PkgComponent pn (ExposedLib lib)) (Private alias) (Constrained vr)
+    | Dependency pn vr libs <- deps, lib <- NonEmptySet.toList libs ]
+
 -- | Convert a Cabal dependency on an executable (build-tools) to a solver-specific dependency.
 convExeDep :: DependencyReason PN -> ExeDependency -> LDep PN
-convExeDep dr (ExeDependency pn exe vr) = LDep dr $ Dep (PkgComponent pn (ExposedExe exe)) (Constrained vr)
+convExeDep dr (ExeDependency pn exe vr) = LDep dr $ Dep (PkgComponent pn (ExposedExe exe)) Public (Constrained vr)
 
 -- | Convert setup dependencies
 convSetupBuildInfo :: PN -> SetupBuildInfo -> FlaggedDeps PN
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Linking.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Linking.hs
index 3e4e2de3ee6..6e9b2f3ae86 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Linking.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Linking.hs
@@ -85,11 +85,11 @@ validateLinking index = (`runReader` initVS) . go
     go :: Tree d c -> Validate (Tree d c)
 
     go (PChoice qpn rdm gr       cs) =
-      PChoice qpn rdm gr       <$> W.traverseWithKey (goP qpn) (fmap go cs)
+      PChoice qpn rdm gr       <$> W.traverseWithKey (goP rdm qpn) (fmap go cs)
     go (FChoice qfn rdm gr t m d cs) =
-      FChoice qfn rdm gr t m d <$> W.traverseWithKey (goF qfn) (fmap go cs)
+      FChoice qfn rdm gr t m d <$> W.traverseWithKey (goF rdm qfn) (fmap go cs)
     go (SChoice qsn rdm gr t     cs) =
-      SChoice qsn rdm gr t     <$> W.traverseWithKey (goS qsn) (fmap go cs)
+      SChoice qsn rdm gr t     <$> W.traverseWithKey (goS rdm qsn) (fmap go cs)
 
     -- For the other nodes we just recurse
     go (GoalChoice rdm           cs) = GoalChoice rdm <$> T.traverse go cs
@@ -97,29 +97,29 @@ validateLinking index = (`runReader` initVS) . go
     go (Fail conflictSet failReason) = return $ Fail conflictSet failReason
 
     -- Package choices
-    goP :: QPN -> POption -> Validate (Tree d c) -> Validate (Tree d c)
-    goP qpn@(Q _pp pn) opt@(POption i _) r = do
+    goP :: RevDepMap -> QPN -> POption -> Validate (Tree d c) -> Validate (Tree d c)
+    goP rdm qpn@(Q _pp pn) opt@(POption i _) r = do
       vs <- ask
       let PInfo deps _ _ _ = vsIndex vs ! pn ! i
-          qdeps            = qualifyDeps (vsQualifyOptions vs) qpn deps
+          qdeps            = qualifyDeps (vsQualifyOptions vs) rdm qpn deps
           newSaved         = M.insert qpn qdeps (vsSaved vs)
-      case execUpdateState (pickPOption qpn opt qdeps) vs of
+      case execUpdateState (pickPOption rdm qpn opt qdeps) vs of
         Left  (cs, err) -> return $ Fail cs (DependenciesNotLinked err)
         Right vs'       -> local (const vs' { vsSaved = newSaved }) r
 
     -- Flag choices
-    goF :: QFN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
-    goF qfn b r = do
+    goF :: RevDepMap -> QFN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
+    goF rdm qfn b r = do
       vs <- ask
-      case execUpdateState (pickFlag qfn b) vs of
+      case execUpdateState (pickFlag rdm qfn b) vs of
         Left  (cs, err) -> return $ Fail cs (DependenciesNotLinked err)
         Right vs'       -> local (const vs') r
 
     -- Stanza choices (much the same as flag choices)
-    goS :: QSN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
-    goS qsn b r = do
+    goS :: RevDepMap -> QSN -> Bool -> Validate (Tree d c) -> Validate (Tree d c)
+    goS rdm qsn b r = do
       vs <- ask
-      case execUpdateState (pickStanza qsn b) vs of
+      case execUpdateState (pickStanza rdm qsn b) vs of
         Left  (cs, err) -> return $ Fail cs (DependenciesNotLinked err)
         Right vs'       -> local (const vs') r
 
@@ -159,9 +159,9 @@ conflict = lift' . Left
 execUpdateState :: UpdateState () -> ValidateState -> Either Conflict ValidateState
 execUpdateState = execStateT . unUpdateState
 
-pickPOption :: QPN -> POption -> FlaggedDeps QPN -> UpdateState ()
-pickPOption qpn (POption i Nothing)    _deps = pickConcrete qpn i
-pickPOption qpn (POption i (Just pp'))  deps = pickLink     qpn i pp' deps
+pickPOption :: RevDepMap -> QPN -> POption -> FlaggedDeps QPN -> UpdateState ()
+pickPOption _rdm qpn (POption i Nothing)    _deps = pickConcrete qpn i
+pickPOption  rdm qpn (POption i (Just pp'))  deps = pickLink rdm qpn i pp' deps
 
 pickConcrete :: QPN -> I -> UpdateState ()
 pickConcrete qpn@(Q pp _) i = do
@@ -177,8 +177,8 @@ pickConcrete qpn@(Q pp _) i = do
       Just lg ->
         makeCanonical lg qpn i
 
-pickLink :: QPN -> I -> PackagePath -> FlaggedDeps QPN -> UpdateState ()
-pickLink qpn@(Q _pp pn) i pp' deps = do
+pickLink :: RevDepMap -> QPN -> I -> PackagePath -> FlaggedDeps QPN -> UpdateState ()
+pickLink rdm qpn@(Q _pp pn) i pp' deps = do
     vs <- get
 
     -- The package might already be in a link group
@@ -209,7 +209,7 @@ pickLink qpn@(Q _pp pn) i pp' deps = do
     updateLinkGroup lgTarget'
 
     -- Make sure all dependencies are linked as well
-    linkDeps target deps
+    linkDeps rdm target deps
 
 makeCanonical :: LinkGroup -> QPN -> I -> UpdateState ()
 makeCanonical lg qpn@(Q pp _) i =
@@ -233,8 +233,8 @@ makeCanonical lg qpn@(Q pp _) i =
 -- because having the direct dependencies in a link group means that we must
 -- have already made or will make sooner or later a link choice for one of these
 -- as well, and cover their dependencies at that point.
-linkDeps :: QPN -> FlaggedDeps QPN -> UpdateState ()
-linkDeps target = \deps -> do
+linkDeps :: RevDepMap -> QPN -> FlaggedDeps QPN -> UpdateState ()
+linkDeps rdm target = \deps -> do
     -- linkDeps is called in two places: when we first link one package to
     -- another, and when we discover more dependencies of an already linked
     -- package after doing some flag assignment. It is therefore important that
@@ -248,7 +248,7 @@ linkDeps target = \deps -> do
 
     go1 :: FlaggedDep QPN -> FlaggedDep QPN -> UpdateState ()
     go1 dep rdep = case (dep, rdep) of
-      (Simple (LDep dr1 (Dep (PkgComponent qpn _) _)) _, ~(Simple (LDep dr2 (Dep (PkgComponent qpn' _) _)) _)) -> do
+      (Simple (LDep dr1 (Dep (PkgComponent qpn _) _is_private1 _)) _, ~(Simple (LDep dr2 (Dep (PkgComponent qpn' _) _is_private2 _)) _)) -> do
         vs <- get
         let lg   = M.findWithDefault (lgSingleton qpn  Nothing) qpn  $ vsLinks vs
             lg'  = M.findWithDefault (lgSingleton qpn' Nothing) qpn' $ vsLinks vs
@@ -276,19 +276,19 @@ linkDeps target = \deps -> do
     requalify :: FlaggedDeps QPN -> UpdateState (FlaggedDeps QPN)
     requalify deps = do
       vs <- get
-      return $ qualifyDeps (vsQualifyOptions vs) target (unqualifyDeps deps)
+      return $ qualifyDeps (vsQualifyOptions vs) rdm target (unqualifyDeps deps)
 
-pickFlag :: QFN -> Bool -> UpdateState ()
-pickFlag qfn b = do
+pickFlag :: RevDepMap -> QFN -> Bool -> UpdateState ()
+pickFlag rdm qfn b = do
     modify $ \vs -> vs { vsFlags = M.insert qfn b (vsFlags vs) }
     verifyFlag qfn
-    linkNewDeps (F qfn) b
+    linkNewDeps rdm (F qfn) b
 
-pickStanza :: QSN -> Bool -> UpdateState ()
-pickStanza qsn b = do
+pickStanza :: RevDepMap -> QSN -> Bool -> UpdateState ()
+pickStanza rdm qsn b = do
     modify $ \vs -> vs { vsStanzas = M.insert qsn b (vsStanzas vs) }
     verifyStanza qsn
-    linkNewDeps (S qsn) b
+    linkNewDeps rdm (S qsn) b
 
 -- | Link dependencies that we discover after making a flag or stanza choice.
 --
@@ -297,15 +297,15 @@ pickStanza qsn b = do
 -- non-trivial link group, then these new dependencies have to be linked as
 -- well. In linkNewDeps, we compute such new dependencies and make sure they are
 -- linked.
-linkNewDeps :: Var QPN -> Bool -> UpdateState ()
-linkNewDeps var b = do
+linkNewDeps :: RevDepMap -> Var QPN -> Bool -> UpdateState ()
+linkNewDeps rdm var b = do
     vs <- get
     let qpn@(Q pp pn)           = varPN var
         qdeps                   = vsSaved vs ! qpn
         lg                      = vsLinks vs ! qpn
         newDeps                 = findNewDeps vs qdeps
         linkedTo                = S.delete pp (lgMembers lg)
-    forM_ (S.toList linkedTo) $ \pp' -> linkDeps (Q pp' pn) newDeps
+    forM_ (S.toList linkedTo) $ \pp' -> linkDeps rdm (Q pp' pn) newDeps
   where
     findNewDeps :: ValidateState -> FlaggedDeps QPN -> FlaggedDeps QPN
     findNewDeps vs = concatMap (findNewDeps' vs)
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Message.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Message.hs
index 810e5121002..b76f36011b3 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Message.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Message.hs
@@ -180,6 +180,7 @@ showConflicts conflicts =
             Just (qpn, MergedPackageConflict False [v] Nothing)
         toMergedConflict (CS.VersionConflict qpn (CS.OrderedVersionRange vr)) =
             Just (qpn, MergedPackageConflict False [] (Just vr))
+        toMergedConflict (CS.PrivateScopeClosureConflict _ _) = Nothing
         toMergedConflict CS.OtherConflict = Nothing
 
     showConflict :: QPN -> MergedPackageConflict -> String
@@ -320,6 +321,7 @@ showFR c Backjump                         = " (backjumping, conflict set: " ++ s
 showFR _ MultipleInstances                = " (multiple instances)"
 showFR c (DependenciesNotLinked msg)      = " (dependencies not linked: " ++ msg ++ "; conflict set: " ++ showConflictSet c ++ ")"
 showFR c CyclicDependencies               = " (cyclic dependencies; conflict set: " ++ showConflictSet c ++ ")"
+showFR c (InvalidPrivateScope qual)       = " (private scopes must contain its closure, but package " ++ showConflictSet c ++ " is not included in the private scope " ++ prettyShow qual ++ ")"
 showFR _ (UnsupportedSpecVer ver)         = " (unsupported spec-version " ++ prettyShow ver ++ ")"
 -- The following are internal failures. They should not occur. In the
 -- interest of not crashing unnecessarily, we still just print an error
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Package.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Package.hs
index ccd0e4d4a70..6b35808902a 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Package.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Package.hs
@@ -11,8 +11,6 @@ module Distribution.Solver.Modular.Package
   , QPV
   , instI
   , makeIndependent
-  , primaryPP
-  , setupPP
   , showI
   , showPI
   , unPN
@@ -77,29 +75,6 @@ instI :: I -> Bool
 instI (I _ (Inst _)) = True
 instI _              = False
 
--- | Is the package in the primary group of packages.  This is used to
--- determine (1) if we should try to establish stanza preferences
--- for this goal, and (2) whether or not a user specified @--constraint@
--- should apply to this dependency (grep 'primaryPP' to see the
--- use sites).  In particular this does not include packages pulled in
--- as setup deps.
---
-primaryPP :: PackagePath -> Bool
-primaryPP (PackagePath _ns q) = go q
-  where
-    go QualToplevel    = True
-    go (QualBase  _)   = True
-    go (QualSetup _)   = False
-    go (QualExe _ _)   = False
-
--- | Is the package a dependency of a setup script.  This is used to
--- establish whether or not certain constraints should apply to this
--- dependency (grep 'setupPP' to see the use sites).
---
-setupPP :: PackagePath -> Bool
-setupPP (PackagePath _ns (QualSetup _)) = True
-setupPP (PackagePath _ns _)         = False
-
 -- | Qualify a target package with its own name so that its dependencies are not
 -- required to be consistent with other targets.
 makeIndependent :: PN -> QPN
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Preference.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Preference.hs
index 9e0d5fb4d22..6f26503a478 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Preference.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Preference.hs
@@ -15,6 +15,7 @@ module Distribution.Solver.Modular.Preference
     , onlyConstrained
     , sortGoals
     , pruneAfterFirstSuccess
+    , rewriteQPN
     ) where
 
 import Prelude ()
@@ -43,6 +44,7 @@ import Distribution.Solver.Modular.Tree
 import Distribution.Solver.Modular.Version
 import qualified Distribution.Solver.Modular.ConflictSet as CS
 import qualified Distribution.Solver.Modular.WeightedPSQ as W
+import Distribution.Solver.Types.ComponentDeps (Component(..))
 
 -- | Update the weights of children under 'PChoice' nodes. 'addWeights' takes a
 -- list of weight-calculating functions in order to avoid sorting the package
@@ -358,6 +360,14 @@ onlyConstrained p = go
     go x
       = x
 
+
+rewriteQPN :: Show d => EndoTreeTrav d QGoalReason
+rewriteQPN = go
+  where
+    go x = x
+
+
+
 -- | Sort all goals using the provided function.
 sortGoals :: (Variable QPN -> Variable QPN -> Ordering) -> EndoTreeTrav d c
 sortGoals variableOrder = go
@@ -420,8 +430,9 @@ deferSetupExeChoices = go
     go x                    = x
 
     noSetupOrExe :: Goal QPN -> Bool
-    noSetupOrExe (Goal (P (Q (PackagePath _ns (QualSetup _)) _)) _) = False
-    noSetupOrExe (Goal (P (Q (PackagePath _ns (QualExe _ _)) _)) _) = False
+    -- TODO: MP defer all component goals?
+    noSetupOrExe (Goal (P (Q (PackagePath (IndependentComponent _ ComponentSetup) _) _)) _) = False
+    noSetupOrExe (Goal (P (Q (PackagePath (IndependentBuildTool {}) _) _)) _) = False
     noSetupOrExe _                                                  = True
 
 -- | Transformation that tries to avoid making weak flag choices early.
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/PrivateScopeClosure.hs b/cabal-install-solver/src/Distribution/Solver/Modular/PrivateScopeClosure.hs
new file mode 100644
index 00000000000..82e3c4f5637
--- /dev/null
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/PrivateScopeClosure.hs
@@ -0,0 +1,126 @@
+{-# LANGUAGE TupleSections #-}
+module Distribution.Solver.Modular.PrivateScopeClosure where
+
+import Control.Exception (assert)
+import Prelude hiding (cycle)
+import qualified Data.Map as M
+
+import Distribution.Solver.Modular.Dependency
+import Distribution.Solver.Modular.Flag
+import Distribution.Solver.Modular.Tree
+import qualified Distribution.Solver.Modular.ConflictSet as CS
+import Distribution.Solver.Types.PackagePath
+
+-- | Find and reject any nodes that would violate the private-dependencies
+-- closure property, which states that all packages within the closure of a
+-- private scope must also be included in the private scope.
+detectInvalidPrivateScopesPhase :: Tree d c -> Tree d c
+detectInvalidPrivateScopesPhase = go
+  where
+    -- Similar to detectCyclesPhase, maybe we could deduplicate
+    go :: Tree d c -> Tree d c
+    go (PChoice qpn rdm gr                         cs) =
+        PChoice qpn rdm gr     $ fmap (checkChild qpn)   (fmap go cs)
+    go (FChoice qfn@(FN qpn _) rdm gr w m d cs) =
+        FChoice qfn rdm gr w m d $ fmap (checkChild qpn) (fmap go cs)
+    go (SChoice qsn@(SN qpn _) rdm gr w     cs) =
+        SChoice qsn rdm gr w   $ fmap (checkChild qpn)   (fmap go cs)
+    go (GoalChoice rdm cs) = GoalChoice rdm (fmap go cs)
+    go x@(Fail _ _) = x
+    go x@(Done _ _) = x
+
+    checkChild :: QPN -> Tree d c -> Tree d c
+    checkChild qpn x@(PChoice _  rdm _       _) = failIfBadClosure qpn rdm x
+    checkChild qpn x@(FChoice _  rdm _ _ _ _ _) = failIfBadClosure qpn rdm x
+    checkChild qpn x@(SChoice _  rdm _ _     _) = failIfBadClosure qpn rdm x
+    checkChild qpn x@(GoalChoice rdm         _) = failIfBadClosure qpn rdm x
+    checkChild _   x@(Fail _ _)                 = x
+    checkChild qpn x@(Done       rdm _)         = failIfBadClosure qpn rdm x
+
+    failIfBadClosure :: QPN -> RevDepMap -> Tree d c -> Tree d c
+    -- An already qualified package can't violate the closure property
+    failIfBadClosure (Q (PackagePath _ (QualAlias _ _ _)) _) _ x = x
+    failIfBadClosure qpn rdm x =
+      case findBadClosures qpn rdm of
+        Nothing     -> x
+        Just (relSet, qual) -> Fail relSet (InvalidPrivateScope qual)
+
+-- | Given the reverse dependency map from a node in the tree, check if the
+-- solution has any bad closures. If it is, return the conflict set containing
+-- the variables violating private deps closures.
+findBadClosures :: QPN -> RevDepMap -> Maybe (ConflictSet, Qualifier)
+findBadClosures pkg rdm =
+  case concatMap (\root@(Q (PackagePath _ ps) _) -> (root,) <$> concatMap (step ps False . snd) (findRevDepsTopLevel root)) roots of
+    (closureBegin@(Q (PackagePath _ ql) _), closureEnd@(Q (PackagePath _ ql') _)):_ ->
+      assert (ql == ql') $
+      return (CS.singletonWithConflict (P pkg) (CS.PrivateScopeClosureConflict closureBegin closureEnd), ql)
+    [] -> Nothing
+  where
+
+    -- Roots of the rev dep map with QualAlias/private scope
+    roots :: [QPN]
+    roots = flip M.foldMapWithKey rdm $
+      \key _ -> case key of
+        Q (PackagePath _ (QualAlias _ _ _)) _ -> [key]
+        _ -> []
+
+    -- Traverse up from a root until a reverse dep in the same private scope is
+    -- found. We only traverse up until we find another private dep in the same
+    -- scope because that is sufficient to complete a "local closure", and
+    -- because we traverse from all root deps in private scopes, we will
+    -- traverse all the "local" closures thus the full closure of each scope... REWRITE and RENAME
+    step :: Qualifier -- ^ This root's qualifier/private scope
+         -> Bool -- ^ Have we found the "goal" package in the "local" closure
+         -> QPN -- ^ Next package in the closure traversal
+         -> [QPN]
+         -- ^ The terminal nodes for each closure violated by this package.
+         -- Empty if the closure property is kept.
+    step rootQual hasFoundGoal next
+      -- We stop at any qualified reverse dep, even if it does not belong to
+      -- the same scope as the one we are checking for the closure property.
+      -- By case analysis:
+      --  * If it is the same scope, we've reached the end of the local
+      --  closure, and if the package has been seen as non-qualified then the
+      --  property is violated
+      --
+      --  * If it is not the same scope, that means "next" in that branch is a
+      --  dep of a private scope goal, but it may not violate the closure
+      --  property for that one. Even if it were to violate the property
+      --  outside of a nested private scope, it doesn't matter because within a
+      --  (nested) private scope it just has to be consistent in
+      --  itself.........
+      | Q (PackagePath _ ps@(QualAlias _ _ _)) _ <- next
+      = if ps == rootQual && hasFoundGoal
+           then [next]
+           else []
+      | otherwise
+      = case findRevDepsTopLevel next of
+        -- If there are no more deps (meaning we didn't stop at any rev-dep in
+        -- a private scope), then we don't have a private scope closure and the
+        -- property is preserved.
+        [] -> []
+        -- Step through all the next reverse deps, failing (by adding terminal
+        -- nodes to the result) if any of the steps violates the closure
+        -- property
+        xs ->
+          -- If the next pkg is our goal, we recurse with "hasFoundGoal =
+          -- True", otherwise with what we had previously
+          let hasFoundGoal' = next == pkg || hasFoundGoal
+           in concatMap (step rootQual hasFoundGoal' . snd) xs
+
+    -- Find the reverse dependencies of this QPN, but in the top-level scope.
+    -- When constructing the closure, starting from a qualified root, we need
+    -- to take into account that the dependencies introduced by the
+    -- private-scoped-depends will be in the top level scope...
+    findRevDepsTopLevel qpn@(Q (PackagePath namespace _) pn) =
+      case (Q (PackagePath namespace QualToplevel) pn) `M.lookup` rdm of
+        Nothing ->
+          -- This means the package we are looking up in the map has only been
+          -- introduced qualified, not at the QualToplevel. This means we look
+          -- it up as is.
+          case qpn `M.lookup` rdm of
+            Nothing -> findError "cannot find node"
+            Just rdeps -> rdeps
+        Just rdeps -> rdeps
+
+    findError = error . ("Distribution.Solver.Modular.PrivateScopeClosure.findBadClosures: " ++)
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Solver.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Solver.hs
index 39bd7bf4690..4ebfaac0132 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Solver.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Solver.hs
@@ -36,6 +36,7 @@ import Distribution.Solver.Modular.Log
 import Distribution.Solver.Modular.Message
 import Distribution.Solver.Modular.Package
 import qualified Distribution.Solver.Modular.Preference as P
+import Distribution.Solver.Modular.PrivateScopeClosure
 import Distribution.Solver.Modular.Validate
 import Distribution.Solver.Modular.Linking
 import Distribution.Solver.Modular.PSQ (PSQ)
@@ -48,7 +49,7 @@ import Distribution.Simple.Setup (BooleanFlag(..))
 #ifdef DEBUG_TRACETREE
 import qualified Distribution.Solver.Modular.ConflictSet as CS
 import qualified Distribution.Solver.Modular.WeightedPSQ as W
-import qualified Distribution.Deprecated.Text as T
+--import qualified Distribution.Deprecated.Text as T
 
 import Debug.Trace.Tree (gtraceJson)
 import Debug.Trace.Tree.Simple
@@ -98,6 +99,8 @@ solve :: SolverConfig                         -- ^ solver parameters
       -> RetryLog Message SolverFailure (Assignment, RevDepMap)
 solve sc cinfo idx pkgConfigDB userPrefs userConstraints userGoals =
   explorePhase      .
+  traceTree "invalid-scopes.json" id .
+  detectInvalidPrivateScopesPhase .
   traceTree "cycles.json" id .
   detectCycles      .
   traceTree "heuristics.json" id .
@@ -143,7 +146,8 @@ solve sc cinfo idx pkgConfigDB userPrefs userConstraints userGoals =
                           OnlyConstrainedAll ->
                             P.onlyConstrained pkgIsExplicit
                           OnlyConstrainedNone ->
-                            id)
+                            id) . prunePhase2
+    prunePhase2      = P.rewriteQPN
     buildPhase       = buildTree idx (independentGoals sc) (S.toList userGoals)
 
     allExplicit = M.keysSet userConstraints `S.union` userGoals
@@ -201,7 +205,7 @@ instance GSimpleTree (Tree d c) where
 
       -- Show package choice
       goP :: QPN -> POption -> Tree d c -> (String, SimpleTree)
-      goP _        (POption (I ver _loc) Nothing)  subtree = (T.display ver, go subtree)
+      goP _        (POption (I ver _loc) Nothing)  subtree = (show ver, go subtree)
       goP (Q _ pn) (POption _           (Just pp)) subtree = (showQPN (Q pp pn), go subtree)
 
       -- Show flag or stanza choice
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Tree.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Tree.hs
index 10d372525b1..e249b3fba34 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Tree.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Tree.hs
@@ -79,6 +79,7 @@ data Tree d c =
 
     -- | We failed to find a solution in this path through the tree
   | Fail ConflictSet FailReason
+  deriving (Show)
 
 -- | A package option is a package instance with an optional linking annotation
 --
@@ -127,6 +128,7 @@ data FailReason = UnsupportedExtension Extension
                 | MultipleInstances
                 | DependenciesNotLinked String
                 | CyclicDependencies
+                | InvalidPrivateScope Qualifier
                 | UnsupportedSpecVer Ver
   deriving (Eq, Show)
 
@@ -143,7 +145,7 @@ data TreeF d c a =
   | GoalChoiceF     RevDepMap                               (PSQ (Goal QPN) a)
   | DoneF           RevDepMap d
   | FailF       ConflictSet FailReason
-  deriving (Functor, Foldable, Traversable)
+  deriving (Functor, Foldable, Traversable, Show)
 
 out :: Tree d c -> TreeF d c (Tree d c)
 out (PChoice    p s i       ts) = PChoiceF    p s i       ts
diff --git a/cabal-install-solver/src/Distribution/Solver/Modular/Validate.hs b/cabal-install-solver/src/Distribution/Solver/Modular/Validate.hs
index cbe6282b6d0..7b9d8a8bf3f 100644
--- a/cabal-install-solver/src/Distribution/Solver/Modular/Validate.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Modular/Validate.hs
@@ -158,7 +158,7 @@ validate = go
   where
     go :: Tree d c -> Validate (Tree d c)
 
-    go (PChoice qpn rdm gr       ts) = PChoice qpn rdm gr <$> W.traverseWithKey (\k -> goP qpn k . go) ts
+    go (PChoice qpn rdm gr       ts) = PChoice qpn rdm gr <$> W.traverseWithKey (\k -> goP rdm qpn k . go) ts
     go (FChoice qfn rdm gr b m d ts) =
       do
         -- Flag choices may occur repeatedly (because they can introduce new constraints
@@ -190,8 +190,8 @@ validate = go
     go (Fail    c fr               ) = pure (Fail c fr)
 
     -- What to do for package nodes ...
-    goP :: QPN -> POption -> Validate (Tree d c) -> Validate (Tree d c)
-    goP qpn@(Q _pp pn) (POption i _) r = do
+    goP :: RevDepMap -> QPN -> POption -> Validate (Tree d c) -> Validate (Tree d c)
+    goP rdm qpn@(Q _pp pn) (POption i _) r = do
       PA ppa pfa psa <- asks pa    -- obtain current preassignment
       extSupported   <- asks supportedExt  -- obtain the supported extensions
       langSupported  <- asks supportedLang -- obtain the supported languages
@@ -204,7 +204,7 @@ validate = go
       -- obtain dependencies and index-dictated exclusions introduced by the choice
       let (PInfo deps comps _ mfr) = idx ! pn ! i
       -- qualify the deps in the current scope
-      let qdeps = qualifyDeps qo qpn deps
+      let qdeps = qualifyDeps qo rdm qpn deps
       -- the new active constraints are given by the instance we have chosen,
       -- plus the dependency information we have for that instance
       let newactives = extractAllDeps pfa psa qdeps
@@ -400,7 +400,7 @@ extend extSupported langSupported pkgPresent newactives ppa = foldM extendSingle
     extendSingle a (LDep dr (Pkg pn vr))  =
       if pkgPresent pn vr then Right a
                           else Left (dependencyReasonToConflictSet dr, MissingPkgconfigPackage pn vr)
-    extendSingle a (LDep dr (Dep dep@(PkgComponent qpn _) ci)) =
+    extendSingle a (LDep dr (Dep dep@(PkgComponent qpn _) _is_private ci)) =
       let mergedDep = M.findWithDefault (MergedDepConstrained []) qpn a
       in  case (\ x -> M.insert qpn x a) <$> merge mergedDep (PkgDep dr dep ci) of
             Left (c, (d, d')) -> Left (c, ConflictingConstraints d d')
@@ -530,7 +530,7 @@ extendRequiredComponents eqpn available = foldM extendSingle
     extendSingle :: Map QPN ComponentDependencyReasons
                  -> LDep QPN
                  -> Either Conflict (Map QPN ComponentDependencyReasons)
-    extendSingle required (LDep dr (Dep (PkgComponent qpn comp) _)) =
+    extendSingle required (LDep dr (Dep (PkgComponent qpn comp) _is_private _)) =
       let compDeps = M.findWithDefault M.empty qpn required
           success = Right $ M.insertWith M.union qpn (M.insert comp dr compDeps) required
       in -- Only check for the existence of the component if its package has
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs b/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
index 8926521673b..aad27391de7 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/ComponentDeps.hs
@@ -83,7 +83,7 @@ type ComponentDep a = (Component, a)
 
 -- | Fine-grained dependencies for a package.
 --
--- Typically used as @ComponentDeps [Dependency]@, to represent the list of
+-- Typically used as @ComponentDeps Dependencies@, to represent the list of
 -- dependencies for each named component within a package.
 --
 newtype ComponentDeps a = ComponentDeps { unComponentDeps :: Map Component a }
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/InstSolverPackage.hs b/cabal-install-solver/src/Distribution/Solver/Types/InstSolverPackage.hs
index 871a0dd15a9..5e76b6a7a24 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/InstSolverPackage.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/InstSolverPackage.hs
@@ -6,7 +6,7 @@ module Distribution.Solver.Types.InstSolverPackage
 import Distribution.Solver.Compat.Prelude
 import Prelude ()
 
-import Distribution.Package ( Package(..), HasMungedPackageId(..), HasUnitId(..) )
+import Distribution.Package ( Package(..), HasMungedPackageId(..), HasUnitId(..), PrivateAlias )
 import Distribution.Solver.Types.ComponentDeps ( ComponentDeps )
 import Distribution.Solver.Types.SolverId
 import Distribution.Types.MungedPackageId
@@ -18,7 +18,7 @@ import Distribution.InstalledPackageInfo (InstalledPackageInfo)
 -- specified by the dependency solver.
 data InstSolverPackage = InstSolverPackage {
       instSolverPkgIPI :: InstalledPackageInfo,
-      instSolverPkgLibDeps :: ComponentDeps [SolverId],
+      instSolverPkgLibDeps :: ComponentDeps [(SolverId, Maybe PrivateAlias)],
       instSolverPkgExeDeps :: ComponentDeps [SolverId]
     }
   deriving (Eq, Show, Generic)
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/PackageConstraint.hs b/cabal-install-solver/src/Distribution/Solver/Types/PackageConstraint.hs
index fbe56380e81..6632290416f 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/PackageConstraint.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/PackageConstraint.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE TypeApplications #-}
 
 -- | Per-package constraints. Package constraints must be respected by the
 -- solver. Multiple constraints for each package can be given, though obviously
@@ -31,6 +32,8 @@ import Distribution.Solver.Types.OptionalStanza
 import Distribution.Solver.Types.PackagePath
 
 import qualified Text.PrettyPrint as Disp
+import Distribution.Solver.Types.ComponentDeps (Component(..))
+import Distribution.Types.Dependency
 
 
 -- | Determines to what packages and in what contexts a
@@ -47,7 +50,13 @@ data ConstraintScope
      -- solving is implemented, and remove this special case for targets.
    = ScopeTarget PackageName
      -- | The package with the specified name and qualifier.
-   | ScopeQualified Qualifier PackageName
+   | ScopeQualified Namespace Qualifier PackageName
+
+    -- TODO Better Comment: Apply a constraint to a private-build-depends scope
+    -- It is not sufficient to have ScopeQualified because we don't have enough
+    -- information in the constraint syntax to fill in the `Component` field of
+    -- `QualAlias`
+   | ScopePrivate PackageName PrivateAlias PackageName
      -- | The package with the specified name when it has a
      -- setup qualifier.
    | ScopeAnySetupQualifier PackageName
@@ -60,24 +69,34 @@ data ConstraintScope
 -- the package with the specified name when that package is a
 -- top-level dependency in the default namespace.
 scopeToplevel :: PackageName -> ConstraintScope
-scopeToplevel = ScopeQualified QualToplevel
+scopeToplevel = ScopeQualified DefaultNamespace QualToplevel
 
 -- | Returns the package name associated with a constraint scope.
 scopeToPackageName :: ConstraintScope -> PackageName
 scopeToPackageName (ScopeTarget pn) = pn
-scopeToPackageName (ScopeQualified _ pn) = pn
+scopeToPackageName (ScopeQualified _ _ pn) = pn
 scopeToPackageName (ScopeAnySetupQualifier pn) = pn
 scopeToPackageName (ScopeAnyQualifier pn) = pn
+scopeToPackageName (ScopePrivate _ _ pn) = pn
 
+-- TODO: Crucial (RM: Why did you write this Matthew?!)
 constraintScopeMatches :: ConstraintScope -> QPN -> Bool
 constraintScopeMatches (ScopeTarget pn) (Q (PackagePath ns q) pn') =
   let namespaceMatches DefaultNamespace = True
       namespaceMatches (Independent namespacePn) = pn == namespacePn
+      namespaceMatches (IndependentComponent {}) = False
+      namespaceMatches (IndependentBuildTool {}) = False
   in namespaceMatches ns && q == QualToplevel && pn == pn'
-constraintScopeMatches (ScopeQualified q pn) (Q (PackagePath _ q') pn') =
-    q == q' && pn == pn'
+constraintScopeMatches (ScopePrivate spn alias c_pn) (Q (PackagePath _qual_ns q) c_pn') =
+  let qualMatches (QualAlias qual_pn _ qual_alias) = spn == qual_pn && alias == qual_alias
+      qualMatches _ = False
+    -- TODO: Check whether any ns should subsume qual_ns (if private constraint scopes grow namespaces...)
+  in qualMatches q && c_pn == c_pn'
+constraintScopeMatches (ScopeQualified ns cq cpn) (Q (PackagePath qual_ns q) cpn') =
+  ns == qual_ns && cq == q && cpn == cpn'
+
 constraintScopeMatches (ScopeAnySetupQualifier pn) (Q pp pn') =
-  let setup (PackagePath _ (QualSetup _)) = True
+  let setup (PackagePath (IndependentComponent _ ComponentSetup) _) = True
       setup _                             = False
   in setup pp && pn == pn'
 constraintScopeMatches (ScopeAnyQualifier pn) (Q _ pn') = pn == pn'
@@ -85,7 +104,8 @@ constraintScopeMatches (ScopeAnyQualifier pn) (Q _ pn') = pn == pn'
 -- | Pretty-prints a constraint scope.
 dispConstraintScope :: ConstraintScope -> Disp.Doc
 dispConstraintScope (ScopeTarget pn) = pretty pn <<>> Disp.text "." <<>> pretty pn
-dispConstraintScope (ScopeQualified q pn) = dispQualifier q <<>> pretty pn
+dispConstraintScope (ScopeQualified ns _q pn) = dispNamespace ns <<>> pretty pn
+dispConstraintScope (ScopePrivate pn alias p) = Disp.text "private." <<>> pretty pn <<>> Disp.text "." <<>> pretty @PrivateAlias alias <<>> Disp.text ":" <<>> pretty p
 dispConstraintScope (ScopeAnySetupQualifier pn) = Disp.text "setup." <<>> pretty pn
 dispConstraintScope (ScopeAnyQualifier pn) = Disp.text "any." <<>> pretty pn
 
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/PackagePath.hs b/cabal-install-solver/src/Distribution/Solver/Types/PackagePath.hs
index 4fc4df25f97..509158ed326 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/PackagePath.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/PackagePath.hs
@@ -2,18 +2,19 @@ module Distribution.Solver.Types.PackagePath
     ( PackagePath(..)
     , Namespace(..)
     , Qualifier(..)
-    , dispQualifier
     , Qualified(..)
     , QPN
+    , dispNamespace
     , dispQPN
     , showQPN
     ) where
 
 import Distribution.Solver.Compat.Prelude
 import Prelude ()
-import Distribution.Package (PackageName)
-import Distribution.Pretty (pretty, flatStyle)
+import Distribution.Package (PackageName, PrivateAlias)
+import Distribution.Pretty (Pretty, pretty, flatStyle)
 import qualified Text.PrettyPrint as Disp
+import Distribution.Solver.Types.ComponentDeps
 
 -- | A package path consists of a namespace and a package path inside that
 -- namespace.
@@ -25,11 +26,18 @@ data PackagePath = PackagePath Namespace Qualifier
 -- Package choices in different namespaces are considered completely independent
 -- by the solver.
 data Namespace =
-    -- | The default namespace
+    -- | A goal which is solved
     DefaultNamespace
 
-    -- | A namespace for a specific build target
+    -- | A goal which is solved per-package
+    -- `--independent-goals`
   | Independent PackageName
+
+
+  | IndependentComponent PackageName Component
+  -- Build-tools are solved per-package so there are consistent build-tools across
+  -- components.
+  | IndependentBuildTool PackageName PackageName
   deriving (Eq, Ord, Show)
 
 -- | Pretty-prints a namespace. The result is either empty or
@@ -37,6 +45,12 @@ data Namespace =
 dispNamespace :: Namespace -> Disp.Doc
 dispNamespace DefaultNamespace = Disp.empty
 dispNamespace (Independent i) = pretty i <<>> Disp.text "."
+dispNamespace (IndependentBuildTool pn btp) = pretty pn <<>> Disp.text ":" <<>>
+                                              pretty btp <<>> Disp.text ":exe."
+dispNamespace (IndependentComponent pn c) = pretty pn <<>> Disp.text ":" <<>> pretty c <<>> Disp.text "."
+
+--dispQualifier (QualSetup pn)  = pretty pn <<>> Disp.text ":setup."
+--dispQualifier (QualExe pn pn2) =
 
 -- | Qualifier of a package within a namespace (see 'PackagePath')
 data Qualifier =
@@ -48,26 +62,9 @@ data Qualifier =
     -- This makes it possible to have base shims.
   | QualBase PackageName
 
-    -- | Setup dependency
-    --
-    -- By rights setup dependencies ought to be nestable; after all, the setup
-    -- dependencies of a package might themselves have setup dependencies, which
-    -- are independent from everything else. However, this very quickly leads to
-    -- infinite search trees in the solver. Therefore we limit ourselves to
-    -- a single qualifier (within a given namespace).
-  | QualSetup PackageName
-
-    -- | If we depend on an executable from a package (via
-    -- @build-tools@), we should solve for the dependencies of that
-    -- package separately (since we're not going to actually try to
-    -- link it.)  We qualify for EACH package separately; e.g.,
-    -- @'Exe' pn1 pn2@ qualifies the @build-tools@ dependency on
-    -- @pn2@ from package @pn1@.  (If we tracked only @pn1@, that
-    -- would require a consistent dependency resolution for all
-    -- of the depended upon executables from a package; if we
-    -- tracked only @pn2@, that would require us to pick only one
-    -- version of an executable over the entire install plan.)
-  | QualExe PackageName PackageName
+  -- A goal which is solved per-component
+  | QualAlias PackageName Component PrivateAlias
+
   deriving (Eq, Ord, Show)
 
 -- | Pretty-prints a qualifier. The result is either empty or
@@ -80,10 +77,11 @@ data Qualifier =
 -- 'Base' qualifier, will always be @base@).
 dispQualifier :: Qualifier -> Disp.Doc
 dispQualifier QualToplevel = Disp.empty
-dispQualifier (QualSetup pn)  = pretty pn <<>> Disp.text ":setup."
-dispQualifier (QualExe pn pn2) = pretty pn <<>> Disp.text ":" <<>>
-                                 pretty pn2 <<>> Disp.text ":exe."
-dispQualifier (QualBase pn)  = pretty pn <<>> Disp.text "."
+dispQualifier (QualBase pn)  = pretty pn <<>> Disp.text ".bb."
+dispQualifier (QualAlias pn c alias) = pretty pn <<>> Disp.text ":" <<>> pretty c <<>> Disp.text ":" <<>> pretty alias <<>> Disp.text "."
+
+instance Pretty Qualifier where
+  pretty = dispQualifier
 
 -- | A qualified entity. Pairs a package path with the entity.
 data Qualified a = Q PackagePath a
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/ResolverPackage.hs b/cabal-install-solver/src/Distribution/Solver/Types/ResolverPackage.hs
index 840e58aff94..f34e5944596 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/ResolverPackage.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/ResolverPackage.hs
@@ -17,6 +17,7 @@ import qualified Distribution.Solver.Types.ComponentDeps as CD
 import Distribution.Compat.Graph (IsNode(..))
 import Distribution.Package (Package(..), HasUnitId(..))
 import Distribution.Simple.Utils (ordNub)
+import Distribution.Types.Dependency (PrivateAlias)
 
 -- | The dependency resolver picks either pre-existing installed packages
 -- or it picks source packages along with package configuration.
@@ -34,7 +35,7 @@ instance Package (ResolverPackage loc) where
   packageId (PreExisting ipkg)     = packageId ipkg
   packageId (Configured  spkg)     = packageId spkg
 
-resolverPackageLibDeps :: ResolverPackage loc -> CD.ComponentDeps [SolverId]
+resolverPackageLibDeps :: ResolverPackage loc -> CD.ComponentDeps [(SolverId, Maybe PrivateAlias)]
 resolverPackageLibDeps (PreExisting ipkg) = instSolverPkgLibDeps ipkg
 resolverPackageLibDeps (Configured spkg) = solverPkgLibDeps spkg
 
@@ -48,5 +49,5 @@ instance IsNode (ResolverPackage loc) where
   nodeKey (Configured spkg) = PlannedId (packageId spkg)
   -- Use dependencies for ALL components
   nodeNeighbors pkg =
-    ordNub $ CD.flatDeps (resolverPackageLibDeps pkg) ++
+    ordNub $ (map fst (CD.flatDeps (resolverPackageLibDeps pkg))) ++
              CD.flatDeps (resolverPackageExeDeps pkg)
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/SolverId.hs b/cabal-install-solver/src/Distribution/Solver/Types/SolverId.hs
index d32ccc17e74..a8bb8a280ea 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/SolverId.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/SolverId.hs
@@ -17,13 +17,10 @@ import Distribution.Package (PackageId, Package(..), UnitId)
 --
 data SolverId = PreExistingId { solverSrcId :: PackageId, solverInstId :: UnitId }
               | PlannedId     { solverSrcId :: PackageId }
-  deriving (Eq, Ord, Generic)
+  deriving (Eq, Ord, Generic, Show)
 
 instance Binary SolverId
 instance Structured SolverId
 
-instance Show SolverId where
-    show = show . solverSrcId
-
 instance Package SolverId where
   packageId = solverSrcId
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/SolverPackage.hs b/cabal-install-solver/src/Distribution/Solver/Types/SolverPackage.hs
index 186f140aefe..85148db46b5 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/SolverPackage.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/SolverPackage.hs
@@ -12,6 +12,7 @@ import Distribution.Solver.Types.ComponentDeps ( ComponentDeps )
 import Distribution.Solver.Types.OptionalStanza
 import Distribution.Solver.Types.SolverId
 import Distribution.Solver.Types.SourcePackage
+import Distribution.Types.Dependency (PrivateAlias)
 
 -- | A 'SolverPackage' is a package specified by the dependency solver.
 -- It will get elaborated into a 'ConfiguredPackage' or even an
@@ -24,7 +25,7 @@ data SolverPackage loc = SolverPackage {
         solverPkgSource  :: SourcePackage loc,
         solverPkgFlags   :: FlagAssignment,
         solverPkgStanzas :: OptionalStanzaSet,
-        solverPkgLibDeps :: ComponentDeps [SolverId],
+        solverPkgLibDeps :: ComponentDeps [(SolverId, Maybe PrivateAlias)],
         solverPkgExeDeps :: ComponentDeps [SolverId]
     }
   deriving (Eq, Show, Generic)
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index ed40a1a85e6..2493f8fe14e 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -443,7 +443,7 @@ depsFromPkgDesc verbosity comp platform = do
         finalizePD
           mempty
           (ComponentRequestedSpec True True)
-          (const True)
+          (\_ _ -> True)
           platform
           cinfo
           []
@@ -457,7 +457,11 @@ depsFromPkgDesc verbosity comp platform = do
         "Reading the list of dependencies from the package description"
       return $ map toPVC bd
   where
-    toPVC (Dependency pn vr _) = PackageVersionConstraint pn vr
+    -- It doesn't seem critical that we report the scope in which the package
+    -- is outdated, because, in order for that report to be consistent with the
+    -- rest of Cabal, we must first consider how cabal outdated and cabal
+    -- freeze work wrt private dependencies (TODO).
+    toPVC (_alias, (Dependency pn vr _)) = PackageVersionConstraint pn vr
 
 -- | Various knobs for customising the behaviour of 'listOutdated'.
 data ListOutdatedSettings = ListOutdatedSettings
diff --git a/cabal-install/src/Distribution/Client/CmdRepl.hs b/cabal-install/src/Distribution/Client/CmdRepl.hs
index 39468a8e545..f5c012da2cf 100644
--- a/cabal-install/src/Distribution/Client/CmdRepl.hs
+++ b/cabal-install/src/Distribution/Client/CmdRepl.hs
@@ -132,7 +132,8 @@ import Distribution.Types.CondTree
   ( CondTree (..)
   )
 import Distribution.Types.Dependency
-  ( Dependency (..)
+  ( Dependencies (..)
+  , Dependency (..)
   , mainLibSet
   )
 import Distribution.Types.Library
@@ -300,7 +301,7 @@ replAction flags@NixStyleFlags{extraFlags = r@ReplFlags{..}, ..} targetStrings g
           sourcePackage =
             fakeProjectSourcePackage projectRoot
               & lSrcpkgDescription . L.condLibrary
-                .~ Just (CondNode library [baseDep] [])
+                .~ Just (CondNode library (Dependencies [baseDep] []) [])
           library = emptyLibrary{libBuildInfo = lBuildInfo}
           lBuildInfo =
             emptyBuildInfo
diff --git a/cabal-install/src/Distribution/Client/Configure.hs b/cabal-install/src/Distribution/Client/Configure.hs
index fc7ea49fe31..4c8f4a5a87f 100644
--- a/cabal-install/src/Distribution/Client/Configure.hs
+++ b/cabal-install/src/Distribution/Client/Configure.hs
@@ -534,7 +534,7 @@ configurePackage
                     CD.nonSetupDeps deps
                 ]
             , configDependencies =
-                [ GivenComponent (packageName srcid) cname uid
+                [ GivenComponent (packageName srcid) cname uid Nothing
                 | ConfiguredId srcid (Just (PkgDesc.CLibName cname)) uid <-
                     CD.nonSetupDeps deps
                 ]
@@ -555,7 +555,7 @@ configurePackage
       pkg = case finalizePD
         flags
         (enableStanzas stanzas)
-        (const True)
+        (\_ _ -> True)
         platform
         comp
         []
diff --git a/cabal-install/src/Distribution/Client/Dependency.hs b/cabal-install/src/Distribution/Client/Dependency.hs
index 37e0cbdf1ee..3d8ae3d70ad 100644
--- a/cabal-install/src/Distribution/Client/Dependency.hs
+++ b/cabal-install/src/Distribution/Client/Dependency.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE TupleSections #-}
+
 -----------------------------------------------------------------------------
 
 -----------------------------------------------------------------------------
@@ -960,10 +962,10 @@ data PackageProblem
   = DuplicateFlag PD.FlagName
   | MissingFlag PD.FlagName
   | ExtraFlag PD.FlagName
-  | DuplicateDeps [PackageId]
-  | MissingDep Dependency
-  | ExtraDep PackageId
-  | InvalidDep Dependency PackageId
+  | DuplicateDeps [(PackageId, Maybe PrivateAlias)]
+  | MissingDep Dependency (Maybe PrivateAlias)
+  | ExtraDep PackageId (Maybe PrivateAlias)
+  | InvalidDep Dependency PackageId (Maybe PrivateAlias)
 
 showPackageProblem :: PackageProblem -> String
 showPackageProblem (DuplicateFlag flag) =
@@ -974,20 +976,23 @@ showPackageProblem (ExtraFlag flag) =
   "extra flag given that is not used by the package: " ++ PD.unFlagName flag
 showPackageProblem (DuplicateDeps pkgids) =
   "duplicate packages specified as selected dependencies: "
-    ++ intercalate ", " (map prettyShow pkgids)
-showPackageProblem (MissingDep dep) =
+    ++ intercalate ", " (map (\(x, y) -> maybe "" ((<> ".") . prettyShow) y <> prettyShow x) pkgids)
+showPackageProblem (MissingDep dep palias) =
   "the package has a dependency "
+    ++ maybe "" ((<> ".") . prettyShow) palias
     ++ prettyShow dep
     ++ " but no package has been selected to satisfy it."
-showPackageProblem (ExtraDep pkgid) =
+showPackageProblem (ExtraDep pkgid palias) =
   "the package configuration specifies "
+    ++ maybe "" ((<> ".") . prettyShow) palias
     ++ prettyShow pkgid
     ++ " but (with the given flag assignment) the package does not actually"
     ++ " depend on any version of that package."
-showPackageProblem (InvalidDep dep pkgid) =
+showPackageProblem (InvalidDep dep pkgid palias) =
   "the package depends on "
     ++ prettyShow dep
     ++ " but the configuration specifies "
+    ++ maybe "" ((<> ".") . prettyShow) palias
     ++ prettyShow pkgid
     ++ " which does not satisfy the dependency."
 
@@ -1012,13 +1017,18 @@ configuredPackageProblems
          | pkgs <-
             CD.nonSetupDeps
               ( fmap
-                  (duplicatesBy (comparing packageName))
+                  (duplicatesBy (comparing (\(x, y) -> (packageName x, y))))
                   specifiedDeps1
               )
          ]
-      ++ [MissingDep dep | OnlyInLeft dep <- mergedDeps]
-      ++ [ExtraDep pkgid | OnlyInRight pkgid <- mergedDeps]
-      ++ [ InvalidDep dep pkgid | InBoth dep pkgid <- mergedDeps, not (packageSatisfiesDependency pkgid dep)
+      ++ [MissingDep dep alias | OnlyInLeft (dep, alias) <- mergedDeps]
+      ++ [ExtraDep pkgid palias | OnlyInRight (pkgid, palias) <- mergedDeps]
+      ++ [ InvalidDep dep pkgid palias
+         | InBoth (dep, palias) (pkgid, _palias) <- mergedDeps
+         , assert
+            (palias == _palias)
+            not
+            (packageSatisfiesDependency pkgid dep)
          ]
     where
       -- TODO: sanity tests on executable deps
@@ -1026,10 +1036,10 @@ configuredPackageProblems
       thisPkgName :: PackageName
       thisPkgName = packageName (srcpkgDescription pkg)
 
-      specifiedDeps1 :: ComponentDeps [PackageId]
-      specifiedDeps1 = fmap (map solverSrcId) specifiedDeps0
+      specifiedDeps1 :: ComponentDeps [(PackageId, Maybe PrivateAlias)]
+      specifiedDeps1 = fmap (map (first solverSrcId)) specifiedDeps0
 
-      specifiedDeps :: [PackageId]
+      specifiedDeps :: [(PackageId, Maybe PrivateAlias)]
       specifiedDeps = CD.flatDeps specifiedDeps1
 
       mergedFlags :: [MergeResult PD.FlagName PD.FlagName]
@@ -1047,19 +1057,19 @@ configuredPackageProblems
 
       dependencyName (Dependency name _ _) = name
 
-      mergedDeps :: [MergeResult Dependency PackageId]
+      mergedDeps :: [MergeResult (Dependency, Maybe PrivateAlias) (PackageId, Maybe PrivateAlias)]
       mergedDeps = mergeDeps requiredDeps specifiedDeps
 
       mergeDeps
-        :: [Dependency]
-        -> [PackageId]
-        -> [MergeResult Dependency PackageId]
+        :: [(Dependency, Maybe PrivateAlias)]
+        -> [(PackageId, Maybe PrivateAlias)]
+        -> [MergeResult (Dependency, Maybe PrivateAlias) (PackageId, Maybe PrivateAlias)]
       mergeDeps required specified =
         let sortNubOn f = nubBy ((==) `on` f) . sortBy (compare `on` f)
          in mergeBy
-              (\dep pkgid -> dependencyName dep `compare` packageName pkgid)
-              (sortNubOn dependencyName required)
-              (sortNubOn packageName specified)
+              (\(dep, alias1) (pkgid, alias2) -> (dependencyName dep, alias1) `compare` (packageName pkgid, alias2))
+              (sortNubOn (first dependencyName) required)
+              (sortNubOn (first packageName) specified)
 
       compSpec = enableStanzas stanzas
       -- TODO: It would be nicer to use ComponentDeps here so we can be more
@@ -1068,13 +1078,13 @@ configuredPackageProblems
       -- have to allow for duplicates when we fold specifiedDeps; once we have
       -- proper ComponentDeps here we should get rid of the `nubOn` in
       -- `mergeDeps`.
-      requiredDeps :: [Dependency]
+      requiredDeps :: [(Dependency, Maybe PrivateAlias)]
       requiredDeps =
         -- TODO: use something lower level than finalizePD
         case finalizePD
           specifiedFlags
           compSpec
-          (const True)
+          (\_ _ -> True)
           platform
           cinfo
           []
@@ -1088,9 +1098,11 @@ configuredPackageProblems
             -- See #3775
             --
             filter
-              ((/= thisPkgName) . dependencyName)
-              (PD.enabledBuildDepends resolvedPkg compSpec)
-              ++ maybe [] PD.setupDepends (PD.setupBuildInfo resolvedPkg)
+              ((/= thisPkgName) . dependencyName . fst)
+              ( map (\(x, y) -> (y, x)) $
+                  PD.enabledBuildDepends resolvedPkg compSpec
+              )
+              ++ maybe [] (map (,Nothing) . PD.setupDepends) (PD.setupBuildInfo resolvedPkg)
           Left _ ->
             error "configuredPackageInvalidDeps internal error"
 
diff --git a/cabal-install/src/Distribution/Client/GenBounds.hs b/cabal-install/src/Distribution/Client/GenBounds.hs
index ae78b50c004..a5dfdd91f3c 100644
--- a/cabal-install/src/Distribution/Client/GenBounds.hs
+++ b/cabal-install/src/Distribution/Client/GenBounds.hs
@@ -39,9 +39,6 @@ import Distribution.Package
   , packageVersion
   , unPackageName
   )
-import Distribution.PackageDescription
-  ( enabledBuildDepends
-  )
 import Distribution.PackageDescription.Configuration
   ( finalizePD
   )
@@ -67,6 +64,7 @@ import Distribution.Types.ComponentRequestedSpec
   ( defaultComponentRequestedSpec
   )
 import Distribution.Types.Dependency
+import Distribution.Types.PackageDescription
 import Distribution.Utils.Path (relativeSymbolicPath)
 import Distribution.Version
   ( LowerBound (..)
@@ -138,7 +136,7 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb globalFlags freezeF
         finalizePD
           mempty
           defaultComponentRequestedSpec
-          (const True)
+          (\_ _ -> True)
           platform
           cinfo
           []
@@ -147,8 +145,12 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb globalFlags freezeF
     Left _ -> putStrLn "finalizePD failed"
     Right (pd, _) -> do
       let needBounds =
-            map depName $
-              filter (not . hasUpperBound . depVersion) $
+            -- TODO: This is not quite right for gen-bounds when private
+            -- dependencies are included: comparing package names is no longer
+            -- sufficient because some packages "duplicated" by also being
+            -- present within some private scope
+            map (depName . snd) $
+              filter (not . hasUpperBound . depVersion . snd) $
                 enabledBuildDepends pd defaultComponentRequestedSpec
 
       pkgs <-
@@ -177,10 +179,10 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb globalFlags freezeF
           traverse_ (notice verbosity . (++ ",") . showBounds padTo) thePkgs
 
 depName :: Dependency -> String
-depName (Dependency pn _ _) = unPackageName pn
+depName = unPackageName . depPkgName
 
 depVersion :: Dependency -> VersionRange
-depVersion (Dependency _ vr _) = vr
+depVersion = depVerRange
 
 -- | The message printed when some dependencies are found to be lacking proper
 -- PVP-mandated bounds.
diff --git a/cabal-install/src/Distribution/Client/Init/Utils.hs b/cabal-install/src/Distribution/Client/Init/Utils.hs
index 12605a669a0..fd0868a3a5f 100644
--- a/cabal-install/src/Distribution/Client/Init/Utils.hs
+++ b/cabal-install/src/Distribution/Client/Init/Utils.hs
@@ -321,7 +321,7 @@ fixupDocFiles v pkgDesc
 mkStringyDep :: String -> Dependency
 mkStringyDep = mkPackageNameDep . mkPackageName
 
-getBaseDep :: Interactive m => InstalledPackageIndex -> InitFlags -> m [Dependency]
+getBaseDep :: Interactive m => InstalledPackageIndex -> InitFlags -> m [P.Dependency]
 getBaseDep pkgIx flags =
   retrieveDependencies
     silent
diff --git a/cabal-install/src/Distribution/Client/Install.hs b/cabal-install/src/Distribution/Client/Install.hs
index a31e4d2ce62..c780febbbe7 100644
--- a/cabal-install/src/Distribution/Client/Install.hs
+++ b/cabal-install/src/Distribution/Client/Install.hs
@@ -1661,7 +1661,7 @@ installReadyPackage
                 CD.nonSetupDeps deps
             ]
         , configDependencies =
-            [ GivenComponent (packageName srcid) cname dep_ipid
+            [ GivenComponent (packageName srcid) cname dep_ipid Nothing
             | ConfiguredId srcid (Just (PackageDescription.CLibName cname)) dep_ipid <-
                 CD.nonSetupDeps deps
             ]
@@ -1677,7 +1677,7 @@ installReadyPackage
       pkg = case finalizePD
         flags
         (enableStanzas stanzas)
-        (const True)
+        (\_ _ -> True)
         platform
         cinfo
         []
diff --git a/cabal-install/src/Distribution/Client/InstallPlan.hs b/cabal-install/src/Distribution/Client/InstallPlan.hs
index 46212baaccc..ffafbaf071b 100644
--- a/cabal-install/src/Distribution/Client/InstallPlan.hs
+++ b/cabal-install/src/Distribution/Client/InstallPlan.hs
@@ -630,7 +630,11 @@ configureInstallPlan configFlags solverPlan =
         -- NB: no support for executable dependencies
         }
       where
-        deps = fmap (concatMap (map configuredId . mapDep)) (solverPkgLibDeps spkg)
+        -- If the private alias of a given dependency matters to the configured
+        -- package deps we should instead add it  to the datatype rather than
+        -- discarding it here. However, we probably only care about the
+        -- dependencies as a whole here (right?), so we simply discard the scope.
+        deps = fmap (concatMap (map configuredId . mapDep . fst)) (solverPkgLibDeps spkg)
 
 -- ------------------------------------------------------------
 
@@ -757,22 +761,23 @@ failed
   -> ([srcpkg], Processing)
 failed plan (Processing processingSet completedSet failedSet) pkgid =
   assert (pkgid `Set.member` processingSet) $
-    assert (all (`Set.notMember` processingSet) (drop 1 newlyFailedIds)) $
-      assert (all (`Set.notMember` completedSet) (drop 1 newlyFailedIds)) $
+    assert (all (`Set.notMember` processingSet) newlyFailedIds) $
+      assert (all (`Set.notMember` completedSet) newlyFailedIds) $
         -- but note that some newlyFailed may already be in the failed set
         -- since one package can depend on two packages that both fail and
         -- so would be in the rev-dep closure for both.
         assert (processingInvariant plan processing') $
-          ( map asConfiguredPackage (drop 1 newlyFailed)
+          ( map asConfiguredPackage newlyFailed
           , processing'
           )
   where
     processingSet' = Set.delete pkgid processingSet
-    failedSet' = failedSet `Set.union` Set.fromList newlyFailedIds
+    failedSet' = failedSet `Set.union` Set.fromList newlyFailedIds `Set.union` Set.singleton pkgid
     newlyFailedIds = map nodeKey newlyFailed
-    newlyFailed =
-      fromMaybe (internalError "failed" "package not in graph") $
-        Graph.revClosure (planGraph plan) [pkgid]
+    newlyFailed = case fromMaybe (internalError "failed" "package not in graph") $
+      Graph.revClosure (planGraph plan) [pkgid] of
+      [] -> error "impossible"
+      _ : tail' -> tail'
     processing' = Processing processingSet' completedSet failedSet'
 
     asConfiguredPackage (Configured pkg) = pkg
diff --git a/cabal-install/src/Distribution/Client/InstallSymlink.hs b/cabal-install/src/Distribution/Client/InstallSymlink.hs
index 1701aa1f652..78f5fd0b613 100644
--- a/cabal-install/src/Distribution/Client/InstallSymlink.hs
+++ b/cabal-install/src/Distribution/Client/InstallSymlink.hs
@@ -205,7 +205,7 @@ symlinkBinaries
           case finalizePD
             flags
             (enableStanzas stanzas)
-            (const True)
+            (\_ _ -> True)
             platform
             cinfo
             []
diff --git a/cabal-install/src/Distribution/Client/List.hs b/cabal-install/src/Distribution/Client/List.hs
index b03211038de..d8bfa969ba7 100644
--- a/cabal-install/src/Distribution/Client/List.hs
+++ b/cabal-install/src/Distribution/Client/List.hs
@@ -651,7 +651,8 @@ mergePackageInfo versionPref installedPkgs sourcePkgs selectedPkg showVer =
             source
       , dependencies =
           combine
-            ( map (SourceDependency . simplifyDependency)
+            -- We discard info (with `snd`) about private scopes because we don't yet report them in cabal list or cabal info (TODO).
+            ( map (SourceDependency . simplifyDependency . snd)
                 . Source.allBuildDepends
             )
             source
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index 151d13ca8ef..d6c554d9e88 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -1531,7 +1531,7 @@ readSourcePackageCabalFile verbosity pkgfilename content =
       unless (null warnings) $
         info verbosity (formatWarnings warnings)
       return pkg
-    (warnings, Left (mspecVersion, errors)) ->
+    (warnings, Left (mspecVersion, errors)) -> do
       throwIO $ CabalFileParseError pkgfilename content errors mspecVersion warnings
   where
     formatWarnings warnings =
diff --git a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
index 2d963b0e07f..d17bbf4b3fe 100644
--- a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
+++ b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
@@ -1158,7 +1158,7 @@ writeBuildReports settings buildContext plan buildOutcomes = do
               Right br -> case buildResultTests br of
                 TestsNotTried -> BuildReports.NotTried
                 TestsOk -> BuildReports.Ok
-         in Just $ (BuildReports.BuildReport (packageId pkg) os arch (compilerId comp) cabalInstallID (elabFlagAssignment pkg) (map (packageId . fst) $ elabLibDependencies pkg) installOutcome docsOutcome testsOutcome, getRepo . elabPkgSourceLocation $ pkg) -- TODO handle failure log files?
+         in Just $ (BuildReports.BuildReport (packageId pkg) os arch (compilerId comp) cabalInstallID (elabFlagAssignment pkg) (map (packageId . (\(a, _, _) -> a)) $ elabLibDependencies pkg) installOutcome docsOutcome testsOutcome, getRepo . elabPkgSourceLocation $ pkg) -- TODO handle failure log files?
       fromPlanPackage _ _ = Nothing
       buildReports = mapMaybe (\x -> fromPlanPackage x (InstallPlan.lookupBuildOutcome x buildOutcomes)) $ InstallPlan.toList plan
 
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs b/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
index d38f07037a6..4e0773484f8 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
@@ -199,7 +199,7 @@ encodePlanAsJson distDirLayout elaboratedInstallPlan elaboratedSharedConfig =
                     J.object $
                       [ comp2str c
                         J..= J.object
-                          ( [ "depends" J..= map (jdisplay . confInstId) (map fst ldeps)
+                          ( [ "depends" J..= map (jdisplay . confInstId) (map (\(p, _, _) -> p) ldeps)
                             , "exe-depends" J..= map (jdisplay . confInstId) edeps
                             ]
                               ++ bin_file c
@@ -212,7 +212,7 @@ encodePlanAsJson distDirLayout elaboratedInstallPlan elaboratedSharedConfig =
                       ]
                in ["components" J..= components]
             ElabComponent comp ->
-              [ "depends" J..= map (jdisplay . confInstId) (map fst $ elabLibDependencies elab)
+              [ "depends" J..= map (jdisplay . confInstId) (map (\(p, _, _) -> p) $ elabLibDependencies elab)
               , "exe-depends" J..= map jdisplay (elabExeDependencies elab)
               , "component-name" J..= J.String (comp2str (compSolverName comp))
               ]
@@ -639,7 +639,7 @@ postBuildProjectStatus
           ]
 
       elabLibDeps :: ElaboratedConfiguredPackage -> [UnitId]
-      elabLibDeps = map (newSimpleUnitId . confInstId) . map fst . elabLibDependencies
+      elabLibDeps = map (newSimpleUnitId . confInstId) . map (\(p, _, _) -> p) . elabLibDependencies
 
       -- Was a build was attempted for this package?
       -- If it doesn't have both a build status and outcome then the answer is no.
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 304331e1f9e..030f97c8254 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -6,7 +6,10 @@
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE TupleSections #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE NoMonoLocalBinds #-}
 
 -- |
 -- /Elaborated: worked out with great care and nicety of detail; executed with great minuteness: elaborate preparations; elaborate care./
@@ -432,6 +435,7 @@ rebuildProjectConfig
             createDirectoryIfMissingVerbose verbosity True distDirectory
             createDirectoryIfMissingVerbose verbosity True distProjectCacheDirectory
 
+          liftIO $ info verbosity "Project settings changed, reconfiguring6..."
           fetchAndReadSourcePackages
             verbosity
             distDirLayout
@@ -1705,12 +1709,10 @@ elaborateInstallPlan
             where
               compSolverName = CD.ComponentSetup
               compComponentName = Nothing
-
-              dep_pkgs = elaborateLibSolverId mapDep =<< CD.setupDeps deps0
-
+              dep_pkgs = [(d', rn) | (d, rn) <- CD.setupDeps deps0, d' <- elaborateLibSolverId mapDep d]
               compLibDependencies =
                 -- MP: No idea what this function does
-                map (\cid -> (configuredId cid, False)) dep_pkgs
+                map (\(cid, rn) -> (configuredId cid, False, rn)) dep_pkgs
               compLinkedLibDependencies = notImpl "compLinkedLibDependencies"
               compOrderLibDependencies = notImpl "compOrderLibDependencies"
 
@@ -1760,7 +1762,7 @@ elaborateInstallPlan
 
                 let do_ cid =
                       let cid' = annotatedIdToConfiguredId . ci_ann_id $ cid
-                       in (cid', False) -- filled in later in pruneInstallPlanPhase2)
+                       in (cid', False, ci_alias cid) -- filled in later in pruneInstallPlanPhase2)
                       -- 2. Read out the dependencies from the ConfiguredComponent cc0
                 let compLibDependencies =
                       -- Nub because includes can show up multiple times
@@ -1875,35 +1877,35 @@ elaborateInstallPlan
               external_lib_dep_sids = CD.select (== compSolverName) deps0
               external_exe_dep_sids = CD.select (== compSolverName) exe_deps0
 
-              external_lib_dep_pkgs = concatMap mapDep external_lib_dep_sids
+              external_exe_dep_sids_raw = [(sid, Nothing) | sid <- external_exe_dep_sids]
 
               -- Combine library and build-tool dependencies, for backwards
               -- compatibility (See issue #5412 and the documentation for
               -- InstallPlan.fromSolverInstallPlan), but prefer the versions
               -- specified as build-tools.
               external_exe_dep_pkgs =
-                concatMap mapDep $
-                  ordNubBy (pkgName . packageId) $
-                    external_exe_dep_sids ++ external_lib_dep_sids
+                [(d, alias) | (sid, alias) <- ordNubBy (pkgName . packageId . fst) $ external_exe_dep_sids_raw ++ external_lib_dep_sids, d <- mapDep sid]
+
+              external_lib_dep_pkgs = [(d, alias) | (sid, alias) <- external_lib_dep_sids, d <- mapDep sid]
 
               external_exe_map =
                 Map.fromList $
                   [ (getComponentId pkg, paths)
-                  | pkg <- external_exe_dep_pkgs
+                  | (pkg, _) <- external_exe_dep_pkgs
                   , let paths = planPackageExePaths pkg
                   ]
               exe_map1 = Map.union external_exe_map $ fmap (\x -> [x]) exe_map
 
               external_lib_cc_map =
-                Map.fromListWith Map.union $
-                  map mkCCMapping external_lib_dep_pkgs
+                Map.fromListWith Map.union (map mkCCMapping external_lib_dep_pkgs)
               external_exe_cc_map =
                 Map.fromListWith Map.union $
                   map mkCCMapping external_exe_dep_pkgs
               external_lc_map =
                 Map.fromList $
                   map mkShapeMapping $
-                    external_lib_dep_pkgs ++ concatMap mapDep external_exe_dep_sids
+                    -- MP: TODO... should these aliases work here as well
+                    (map fst external_lib_dep_pkgs ++ concatMap (mapDep . fst) external_exe_dep_sids_raw)
 
               compPkgConfigDependencies =
                 [ ( pn
@@ -2037,9 +2039,10 @@ elaborateInstallPlan
 
             filterExt' :: [(ConfiguredId, a)] -> [(ConfiguredId, a)]
             filterExt' = filter (isExt . fst)
+            filterExt'' = filter (isExt . (\(d, _, _) -> d))
 
             pkgLibDependencies =
-              buildComponentDeps (filterExt' . compLibDependencies)
+              buildComponentDeps (filterExt'' . compLibDependencies)
             pkgExeDependencies =
               buildComponentDeps (filterExt . compExeDependencies)
             pkgExeDependencyPaths =
@@ -2106,7 +2109,7 @@ elaborateInstallPlan
             elabPkgDescription = case PD.finalizePD
               flags
               elabEnabledSpec
-              (const True)
+              (\_ _ -> True)
               platform
               (compilerInfo compiler)
               []
@@ -2173,7 +2176,7 @@ elaborateInstallPlan
                 elabSetupScriptStyle
                 elabPkgDescription
                 libDepGraph
-                deps0
+                (fmap (map fst) deps0)
             elabSetupPackageDBStack = buildAndRegisterDbs
 
             elabInplaceBuildPackageDBStack = inplacePackageDbs
@@ -2452,42 +2455,45 @@ matchElabPkg p elab =
 -- and 'ComponentName' to the 'ComponentId' that should be used
 -- in this case.
 mkCCMapping
-  :: ElaboratedPlanPackage
-  -> (PackageName, Map ComponentName (AnnotatedId ComponentId))
-mkCCMapping =
-  InstallPlan.foldPlanPackage
-    ( \ipkg ->
-        ( packageName ipkg
-        , Map.singleton
-            (ipiComponentName ipkg)
-            -- TODO: libify
-            ( AnnotatedId
-                { ann_id = IPI.installedComponentId ipkg
-                , ann_pid = packageId ipkg
-                , ann_cname = IPI.sourceComponentName ipkg
-                }
+  :: (ElaboratedPlanPackage, Maybe PrivateAlias)
+  -> ((PackageName, Maybe PrivateAlias), Map ComponentName ((AnnotatedId ComponentId)))
+mkCCMapping (ep, alias) = foldpp ep
+  where
+    foldpp =
+      InstallPlan.foldPlanPackage
+        ( \ipkg ->
+            ( (packageName ipkg, alias)
+            , Map.singleton
+                (ipiComponentName ipkg)
+                -- TODO: libify
+                ( AnnotatedId
+                    { ann_id = IPI.installedComponentId ipkg
+                    , ann_pid = packageId ipkg
+                    , ann_cname = IPI.sourceComponentName ipkg
+                    }
+                )
             )
         )
-    )
-    $ \elab ->
-      let mk_aid cn =
-            AnnotatedId
-              { ann_id = elabComponentId elab
-              , ann_pid = packageId elab
-              , ann_cname = cn
-              }
-       in ( packageName elab
-          , case elabPkgOrComp elab of
-              ElabComponent comp ->
-                case compComponentName comp of
-                  Nothing -> Map.empty
-                  Just n -> Map.singleton n (mk_aid n)
-              ElabPackage _ ->
-                Map.fromList $
-                  map
-                    (\comp -> let cn = Cabal.componentName comp in (cn, mk_aid cn))
-                    (Cabal.pkgBuildableComponents (elabPkgDescription elab))
-          )
+        $ \elab ->
+          let mk_aid cn =
+                ( AnnotatedId
+                    { ann_id = elabComponentId elab
+                    , ann_pid = packageId elab
+                    , ann_cname = cn
+                    }
+                )
+           in ( (packageName elab, alias)
+              , case elabPkgOrComp elab of
+                  ElabComponent comp ->
+                    case compComponentName comp of
+                      Nothing -> Map.empty
+                      Just n -> Map.singleton n (mk_aid n)
+                  ElabPackage _ ->
+                    Map.fromList $
+                      map
+                        (\comp -> let cn = Cabal.componentName comp in (cn, mk_aid cn))
+                        (Cabal.pkgBuildableComponents (elabPkgDescription elab))
+              )
 
 -- | Given an 'ElaboratedPlanPackage', generate the mapping from 'ComponentId'
 -- to the shape of this package, as per mix-in linking.
@@ -3519,7 +3525,7 @@ pruneInstallPlanPass2 pkgs =
       where
         -- We initially assume that all the dependencies are external (hence the boolean is always
         -- False) and here we correct the dependencies so the right packages are marked promised.
-        addInternal (cid, _) = (cid, (cid `Set.member` inMemoryTargets))
+        addInternal (cid, _, pn) = (cid, (cid `Set.member` inMemoryTargets), pn)
 
         libTargetsRequiredForRevDeps =
           [ c
@@ -3681,7 +3687,7 @@ setupHsScriptOptions
       , usePackageIndex = Nothing
       , useDependencies =
           [ (uid, srcid)
-          | (ConfiguredId srcid (Just (CLibName LMainLibName)) uid, _) <-
+          | (ConfiguredId srcid (Just (CLibName LMainLibName)) uid, _, _) <-
               elabSetupDependencies elab
           ]
       , useDependenciesExclusive = True
@@ -3893,14 +3899,14 @@ setupHsConfigureFlags
       -- enough info anyway)
       --
       configDependencies =
-        [ cidToGivenComponent cid
-        | (cid, is_internal) <- elabLibDependencies elab
+        [ cidToGivenComponent alias cid
+        | (cid, is_internal, alias) <- elabLibDependencies elab
         , not is_internal
         ]
 
       configPromisedDependencies =
-        [ cidToGivenComponent cid
-        | (cid, is_internal) <- elabLibDependencies elab
+        [ cidToGivenComponent alias cid
+        | (cid, is_internal, alias) <- elabLibDependencies elab
         , is_internal
         ]
 
@@ -3908,7 +3914,7 @@ setupHsConfigureFlags
         case elabPkgOrComp of
           ElabPackage _ ->
             [ thisPackageVersionConstraint srcid
-            | (ConfiguredId srcid _ _uid, _) <- elabLibDependencies elab
+            | (ConfiguredId srcid _ _uid, _, _) <- elabLibDependencies elab
             ]
           ElabComponent _ -> []
 
@@ -3931,8 +3937,8 @@ setupHsConfigureFlags
       configUseResponseFiles = mempty
       configAllowDependingOnPrivateLibs = Flag $ not $ libraryVisibilitySupported pkgConfigCompiler
 
-      cidToGivenComponent :: ConfiguredId -> GivenComponent
-      cidToGivenComponent (ConfiguredId srcid mb_cn cid) = GivenComponent (packageName srcid) ln cid
+      cidToGivenComponent :: Maybe PrivateAlias -> ConfiguredId -> GivenComponent
+      cidToGivenComponent alias (ConfiguredId srcid mb_cn cid) = GivenComponent (packageName srcid) ln cid alias
         where
           ln = case mb_cn of
             Just (CLibName lname) -> lname
@@ -4195,7 +4201,7 @@ packageHashInputs
             ElabPackage (ElaboratedPackage{..}) ->
               Set.fromList $
                 [ confInstId dep
-                | (dep, _) <- CD.select relevantDeps pkgLibDependencies
+                | (dep, _, _) <- CD.select relevantDeps pkgLibDependencies
                 ]
                   ++ [ confInstId dep
                      | dep <- CD.select relevantDeps pkgExeDependencies
@@ -4204,7 +4210,7 @@ packageHashInputs
               Set.fromList
                 ( map
                     confInstId
-                    ( map fst (compLibDependencies comp)
+                    ( map (\(d, _, _) -> d) (compLibDependencies comp)
                         ++ compExeDependencies comp
                     )
                 )
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning/SetupPolicy.hs b/cabal-install/src/Distribution/Client/ProjectPlanning/SetupPolicy.hs
index 86bc044342e..d2fc113e21e 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning/SetupPolicy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning/SetupPolicy.hs
@@ -176,7 +176,7 @@ instance IsNode NonSetupLibDepSolverPlanPackage where
     nodeKey spkg
 
   nodeNeighbors (NonSetupLibDepSolverPlanPackage spkg) =
-    ordNub $ CD.nonSetupDeps (resolverPackageLibDeps spkg)
+    ordNub $ map fst (CD.nonSetupDeps (resolverPackageLibDeps spkg))
 
 -- | Work out which version of the Cabal we will be using to talk to the
 -- Setup.hs interface for this package.
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning/Types.hs b/cabal-install/src/Distribution/Client/ProjectPlanning/Types.hs
index f344db1e389..e90d187c4b2 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning/Types.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning/Types.hs
@@ -179,7 +179,13 @@ showElaboratedInstallPlan = InstallPlan.showInstallPlan_gen showNode
 
         installed_deps = map pretty . nodeNeighbors
 
-        local_deps cfg = [(if internal then text "+" else mempty) <> pretty (confInstId uid) | (uid, internal) <- elabLibDependencies cfg]
+        local_deps cfg =
+          [ (if internal then text "+" else mempty) <> mpalias <> pretty (confInstId uid)
+          | (uid, internal, alias) <- elabLibDependencies cfg
+          , let mpalias = case alias of
+                  Nothing -> mempty
+                  Just al -> pretty al <> text "."
+          ]
 
 -- TODO: [code cleanup] decide if we really need this, there's not much in it, and in principle
 --      even platform and compiler could be different if we're building things
@@ -569,13 +575,13 @@ elabOrderLibDependencies elab =
     ElabPackage pkg ->
       map (newSimpleUnitId . confInstId) $
         ordNub $
-          CD.flatDeps (map fst <$> pkgLibDependencies pkg)
+          CD.flatDeps (map (\(cid, _, _) -> cid) <$> pkgLibDependencies pkg)
     ElabComponent comp -> compOrderLibDependencies comp
 
 -- | The library dependencies (i.e., the libraries we depend on, NOT
 -- the dependencies of the library), NOT including setup dependencies.
 -- These are passed to the @Setup@ script via @--dependency@ or @--promised-dependency@.
-elabLibDependencies :: ElaboratedConfiguredPackage -> [(ConfiguredId, Bool)]
+elabLibDependencies :: ElaboratedConfiguredPackage -> [(ConfiguredId, Bool, Maybe PrivateAlias)]
 elabLibDependencies elab =
   case elabPkgOrComp elab of
     ElabPackage pkg -> ordNub (CD.nonSetupDeps (pkgLibDependencies pkg))
@@ -609,7 +615,7 @@ elabExeDependencyPaths elab =
 -- | The setup dependencies (the library dependencies of the setup executable;
 -- note that it is not legal for setup scripts to have executable
 -- dependencies at the moment.)
-elabSetupDependencies :: ElaboratedConfiguredPackage -> [(ConfiguredId, Bool)]
+elabSetupDependencies :: ElaboratedConfiguredPackage -> [(ConfiguredId, Bool, Maybe PrivateAlias)]
 elabSetupDependencies elab =
   case elabPkgOrComp elab of
     ElabPackage pkg -> CD.setupDeps (pkgLibDependencies pkg)
@@ -669,7 +675,7 @@ data ElaboratedComponent = ElaboratedComponent
   , compComponentName :: Maybe ComponentName
   -- ^ The name of the component to be built.  Nothing if
   -- it's a setup dep.
-  , compLibDependencies :: [(ConfiguredId, Bool)]
+  , compLibDependencies :: [(ConfiguredId, Bool, Maybe PrivateAlias)]
   -- ^ The *external* library dependencies of this component.  We
   -- pass this to the configure script. The Bool indicates whether the
   -- dependency is a promised dependency (True) or not (False).
@@ -716,7 +722,7 @@ compOrderExeDependencies = map (newSimpleUnitId . confInstId) . compExeDependenc
 
 data ElaboratedPackage = ElaboratedPackage
   { pkgInstalledId :: InstalledPackageId
-  , pkgLibDependencies :: ComponentDeps [(ConfiguredId, Bool)]
+  , pkgLibDependencies :: ComponentDeps [(ConfiguredId, Bool, Maybe PrivateAlias)]
   -- ^ The exact dependencies (on other plan packages)
   -- The boolean value indicates whether the dependency is a promised dependency
   -- or not.
@@ -788,7 +794,7 @@ whyNotPerComponent = \case
 -- which can be useful in some circumstances.
 pkgOrderDependencies :: ElaboratedPackage -> ComponentDeps [UnitId]
 pkgOrderDependencies pkg =
-  fmap (map (newSimpleUnitId . confInstId)) (map fst <$> pkgLibDependencies pkg)
+  fmap (map (newSimpleUnitId . confInstId)) (map (\(cid, _, _) -> cid) <$> pkgLibDependencies pkg)
     `Mon.mappend` fmap (map (newSimpleUnitId . confInstId)) (pkgExeDependencies pkg)
 
 -- | This is used in the install plan to indicate how the package will be
diff --git a/cabal-install/src/Distribution/Client/ScriptUtils.hs b/cabal-install/src/Distribution/Client/ScriptUtils.hs
index 20f644668e6..5fe28f0cb63 100644
--- a/cabal-install/src/Distribution/Client/ScriptUtils.hs
+++ b/cabal-install/src/Distribution/Client/ScriptUtils.hs
@@ -101,7 +101,8 @@ import Distribution.Fields
   , readFields
   )
 import Distribution.PackageDescription
-  ( ignoreConditions
+  ( Dependencies (..)
+  , ignoreConditions
   )
 import Distribution.PackageDescription.FieldGrammar
   ( executableFieldGrammar
@@ -463,10 +464,11 @@ updateContextAndWriteProjectFile ctx scriptPath scriptExecutable = do
 
   absScript <- unsafeMakeSymbolicPath . makeRelative (normalise projectRoot) <$> canonicalizePath scriptPath
   let
+    deps = Dependencies (targetBuildDepends $ buildInfo executable) (targetPrivateBuildDepends $ buildInfo executable)
     sourcePackage =
       fakeProjectSourcePackage projectRoot
         & lSrcpkgDescription . L.condExecutables
-          .~ [(scriptComponenetName scriptPath, CondNode executable (targetBuildDepends $ buildInfo executable) [])]
+          .~ [(scriptComponenetName scriptPath, CondNode executable deps [])]
     executable =
       scriptExecutable
         & L.modulePath .~ absScript
diff --git a/cabal-install/src/Distribution/Client/Setup.hs b/cabal-install/src/Distribution/Client/Setup.hs
index 95ac8dbffff..bf8ef8aad13 100644
--- a/cabal-install/src/Distribution/Client/Setup.hs
+++ b/cabal-install/src/Distribution/Client/Setup.hs
@@ -744,14 +744,15 @@ filterConfigureFlags' flags cabalLibVersion
           -- (public sublibraries), so we convert it to the legacy
           -- --dependency=pkg_or_internal_component=cid
           configDependencies =
-            let convertToLegacyInternalDep (GivenComponent _ (LSubLibName cn) cid) =
+            let convertToLegacyInternalDep (GivenComponent _ (LSubLibName cn) cid alias) =
                   Just $
                     GivenComponent
                       (unqualComponentNameToPackageName cn)
                       LMainLibName
                       cid
-                convertToLegacyInternalDep (GivenComponent pn LMainLibName cid) =
-                  Just $ GivenComponent pn LMainLibName cid
+                      alias
+                convertToLegacyInternalDep (GivenComponent pn LMainLibName cid alias) =
+                  Just $ GivenComponent pn LMainLibName cid alias
              in catMaybes $ convertToLegacyInternalDep <$> configDependencies flags
         , -- Cabal < 2.5 doesn't know about '--allow-depending-on-private-libs'.
           configAllowDependingOnPrivateLibs = NoFlag
diff --git a/cabal-install/src/Distribution/Client/SolverInstallPlan.hs b/cabal-install/src/Distribution/Client/SolverInstallPlan.hs
index f4422080a4b..a0a8fcd0baa 100644
--- a/cabal-install/src/Distribution/Client/SolverInstallPlan.hs
+++ b/cabal-install/src/Distribution/Client/SolverInstallPlan.hs
@@ -60,6 +60,7 @@ import Distribution.Package
   , PackageId
   , PackageIdentifier (..)
   , PackageName
+  , PrivateAlias (..)
   , packageName
   , packageVersion
   )
@@ -81,6 +82,7 @@ import Distribution.Solver.Types.SolverPackage
 import Data.Array ((!))
 import qualified Data.Foldable as Foldable
 import qualified Data.Graph as OldGraph
+import qualified Data.List as List
 import qualified Data.Map as Map
 import Distribution.Compat.Graph (Graph, IsNode (..))
 import qualified Distribution.Compat.Graph as Graph
@@ -313,7 +315,7 @@ nonSetupClosure index pkgids0 = closure Graph.empty pkgids0
             Nothing -> closure completed' pkgids'
               where
                 completed' = Graph.insert pkg completed
-                pkgids' = CD.nonSetupDeps (resolverPackageLibDeps pkg) ++ pkgids
+                pkgids' = map fst (CD.nonSetupDeps (resolverPackageLibDeps pkg)) ++ pkgids
 
 -- | Compute the root sets of a plan
 --
@@ -349,7 +351,7 @@ libraryRoots index =
 setupRoots :: SolverPlanIndex -> [[SolverId]]
 setupRoots =
   filter (not . null)
-    . map (CD.setupDeps . resolverPackageLibDeps)
+    . map (map fst . CD.setupDeps . resolverPackageLibDeps)
     . Foldable.toList
 
 -- | Given a package index where we assume we want to use all the packages
@@ -365,42 +367,56 @@ dependencyInconsistencies'
   :: SolverPlanIndex
   -> [(PackageName, [(PackageIdentifier, Version)])]
 dependencyInconsistencies' index =
-  [ (name, [(pid, packageVersion dep) | (dep, pids) <- uses, pid <- pids])
+  [ (name, [(pid, packageVersion dep) | (dep, pids) <- map snd uses, pid <- pids])
   | (name, ipid_map) <- Map.toList inverseIndex
-  , let uses = Map.elems ipid_map
-  , reallyIsInconsistent (map fst uses)
+  , let uses = Map.toAscList ipid_map -- We need a sorted list with (aliases, packages) (aliases before packages) to call groupBy on.
+  , any (reallyIsInconsistent . map (fst . snd)) $
+      -- We group together all packages without a private alias, and those with
+      -- private aliases by its scope name AND the SolverId of the package
+      -- (because, across packages, there may exist scopes with the same name).
+      List.groupBy
+        ( \x y -> case (x, y) of
+            (((Nothing, _), _), (_, _)) -> False
+            ((_, _), ((Nothing, _), _)) -> False
+            (((aliasA, sidA), _), ((aliasB, sidB), _))
+              | aliasA == aliasB ->
+                  sidA == sidB
+              | otherwise ->
+                  False
+        )
+        uses
   ]
   where
     -- For each package name (of a dependency, somewhere)
     --   and each installed ID of that package
     --     the associated package instance
-    --     and a list of reverse dependencies (as source IDs)
-    inverseIndex :: Map PackageName (Map SolverId (SolverPlanPackage, [PackageId]))
+    --     and a list of reverse dependencies (as source IDs) and the possible private scope of each revdep
+    inverseIndex :: Map PackageName (Map (Maybe PrivateAlias, SolverId) (SolverPlanPackage, [PackageId]))
     inverseIndex =
       Map.fromListWith
         (Map.unionWith (\(a, b) (_, b') -> (a, b ++ b')))
-        [ (packageName dep, Map.fromList [(sid, (dep, [packageId pkg]))])
+        [ (packageName dep, Map.fromList [((palias, sid), (dep, [(packageId pkg)]))])
         | -- For each package @pkg@
         pkg <- Foldable.toList index
         , -- Find out which @sid@ @pkg@ depends on
-        sid <- CD.nonSetupDeps (resolverPackageLibDeps pkg)
+        (sid, palias) <- CD.nonSetupDeps (resolverPackageLibDeps pkg)
         , -- And look up those @sid@ (i.e., @sid@ is the ID of @dep@)
         Just dep <- [Graph.lookup sid index]
         ]
 
     -- If, in a single install plan, we depend on more than one version of a
-    -- package, then this is ONLY okay in the (rather special) case that we
-    -- depend on precisely two versions of that package, and one of them
-    -- depends on the other. This is necessary for example for the base where
-    -- we have base-3 depending on base-4.
-    reallyIsInconsistent :: [SolverPlanPackage] -> Bool
+    -- package in the same top-level or private scope, then this is ONLY okay
+    -- in the (rather special) case that we depend on precisely two versions of
+    -- that package, and one of them depends on the other. This is necessary
+    -- for example for the base where we have base-3 depending on base-4.
+    reallyIsInconsistent :: ([SolverPlanPackage]) -> Bool
     reallyIsInconsistent [] = False
     reallyIsInconsistent [_p] = False
     reallyIsInconsistent [p1, p2] =
       let pid1 = nodeKey p1
           pid2 = nodeKey p2
-       in pid1 `notElem` CD.nonSetupDeps (resolverPackageLibDeps p2)
-            && pid2 `notElem` CD.nonSetupDeps (resolverPackageLibDeps p1)
+       in pid1 `notElem` map fst (CD.nonSetupDeps (resolverPackageLibDeps p2))
+            && pid2 `notElem` map fst (CD.nonSetupDeps (resolverPackageLibDeps p1))
     reallyIsInconsistent _ = True
 
 -- | The graph of packages (nodes) and dependencies (edges) must be acyclic.
diff --git a/cabal-install/src/Distribution/Client/Targets.hs b/cabal-install/src/Distribution/Client/Targets.hs
index 1a37c9c73b9..afef8c30223 100644
--- a/cabal-install/src/Distribution/Client/Targets.hs
+++ b/cabal-install/src/Distribution/Client/Targets.hs
@@ -84,7 +84,8 @@ import Distribution.Types.PackageVersionConstraint
   )
 
 import Distribution.PackageDescription
-  ( GenericPackageDescription
+  ( ComponentName
+  , GenericPackageDescription
   )
 import Distribution.Simple.Utils
   ( dieWithException
@@ -106,6 +107,8 @@ import qualified Data.Map as Map
 import Distribution.Client.Errors
 import qualified Distribution.Client.GZipUtils as GZipUtils
 import qualified Distribution.Compat.CharParsing as P
+import Distribution.Solver.Types.ComponentDeps
+import Distribution.Types.Dependency
 import Distribution.Utils.Path (makeSymbolicPath)
 import Network.URI
   ( URI (..)
@@ -613,6 +616,7 @@ data UserQualifier
     UserQualSetup PackageName
   | -- | Executable dependency.
     UserQualExe PackageName PackageName
+  | UserQualComp PackageName ComponentName
   deriving (Eq, Show, Generic)
 
 instance Binary UserQualifier
@@ -623,6 +627,7 @@ instance Structured UserQualifier
 data UserConstraintScope
   = -- | Scope that applies to the package when it has the specified qualifier.
     UserQualified UserQualifier PackageName
+  | UserPrivateQualifier PackageName PrivateAlias PackageName
   | -- | Scope that applies to the package when it has a setup qualifier.
     UserAnySetupQualifier PackageName
   | -- | Scope that applies to the package when it has any qualifier.
@@ -632,14 +637,16 @@ data UserConstraintScope
 instance Binary UserConstraintScope
 instance Structured UserConstraintScope
 
-fromUserQualifier :: UserQualifier -> Qualifier
-fromUserQualifier UserQualToplevel = QualToplevel
-fromUserQualifier (UserQualSetup name) = QualSetup name
-fromUserQualifier (UserQualExe name1 name2) = QualExe name1 name2
+fromUserQualifier :: UserQualifier -> Namespace
+fromUserQualifier UserQualToplevel = DefaultNamespace
+fromUserQualifier (UserQualSetup pn) = IndependentComponent pn ComponentSetup
+fromUserQualifier (UserQualExe pn bpn) = IndependentBuildTool pn bpn
+fromUserQualifier (UserQualComp pn cn) = IndependentComponent pn (componentNameToComponent cn)
 
 fromUserConstraintScope :: UserConstraintScope -> ConstraintScope
 fromUserConstraintScope (UserQualified q pn) =
-  ScopeQualified (fromUserQualifier q) pn
+  ScopeQualified (fromUserQualifier q) QualToplevel pn
+fromUserConstraintScope (UserPrivateQualifier pn alias cpn) = ScopePrivate pn alias cpn
 fromUserConstraintScope (UserAnySetupQualifier pn) = ScopeAnySetupQualifier pn
 fromUserConstraintScope (UserAnyQualifier pn) = ScopeAnyQualifier pn
 
@@ -658,6 +665,7 @@ userConstraintPackageName (UserConstraint scope _) = scopePN scope
     scopePN (UserQualified _ pn) = pn
     scopePN (UserAnyQualifier pn) = pn
     scopePN (UserAnySetupQualifier pn) = pn
+    scopePN (UserPrivateQualifier _ _ pn) = pn
 
 userToPackageConstraint :: UserConstraint -> PackageConstraint
 userToPackageConstraint (UserConstraint scope prop) =
@@ -706,10 +714,24 @@ instance Parsec UserConstraint where
           withDot pn
             | pn == mkPackageName "any" = UserAnyQualifier <$> parsec
             | pn == mkPackageName "setup" = UserAnySetupQualifier <$> parsec
+            | pn == mkPackageName "private" = do
+                qpn <- parsec
+                _ <- P.char '.'
+                alias <- parsec
+                _ <- P.char ':'
+                cpn <- parsec
+                return $ UserPrivateQualifier qpn alias cpn
             | otherwise = P.unexpected $ "constraint scope: " ++ unPackageName pn
 
-          withColon :: PackageName -> m UserConstraintScope
-          withColon pn =
+          withColon, setupQual, compQual :: PackageName -> m UserConstraintScope
+          withColon pn = setupQual pn <|> compQual pn
+
+          compQual pn = do
+            comp_qual <- UserQualComp pn <$> parsec
+            void $ P.char '.'
+            UserQualified comp_qual <$> parsec
+
+          setupQual pn =
             UserQualified (UserQualSetup pn)
               <$ P.string "setup."
               <*> parsec
diff --git a/cabal-install/src/Distribution/Client/Types/ConfiguredPackage.hs b/cabal-install/src/Distribution/Client/Types/ConfiguredPackage.hs
index 0b7d62e7e77..aefb7bee26f 100644
--- a/cabal-install/src/Distribution/Client/Types/ConfiguredPackage.hs
+++ b/cabal-install/src/Distribution/Client/Types/ConfiguredPackage.hs
@@ -41,7 +41,7 @@ data ConfiguredPackage loc = ConfiguredPackage
   , confPkgDeps :: CD.ComponentDeps [ConfiguredId]
   -- ^ set of exact dependencies (installed or source).
   --
-  -- These must be consistent with the 'buildDepends'
+  -- These must be consistent with the 'buildDepends' and 'privateBuildDepends'
   -- in the 'PackageDescription' that you'd get by
   -- applying the flag assignment and optional stanzas.
   }
diff --git a/cabal-install/tests/IntegrationTests2.hs b/cabal-install/tests/IntegrationTests2.hs
index 6579b2ddcc2..cc955240fc7 100644
--- a/cabal-install/tests/IntegrationTests2.hs
+++ b/cabal-install/tests/IntegrationTests2.hs
@@ -468,7 +468,7 @@ testTargetSelectorAmbiguous reportSubCase = do
           condLibrary        = Nothing,
           condSubLibraries   = [],
           condForeignLibs    = [],
-          condExecutables    = [ ( exeName exe, CondNode exe [] [] )
+          condExecutables    = [ ( exeName exe, CondNode exe mempty [] )
                                | exe <- exes ],
           condTestSuites     = [],
           condBenchmarks     = []
diff --git a/cabal-install/tests/UnitTests.hs b/cabal-install/tests/UnitTests.hs
index 8434f623e82..a7d94e93890 100644
--- a/cabal-install/tests/UnitTests.hs
+++ b/cabal-install/tests/UnitTests.hs
@@ -24,11 +24,12 @@ import qualified UnitTests.Distribution.Solver.Modular.RetryLog
 import qualified UnitTests.Distribution.Solver.Modular.Solver
 import qualified UnitTests.Distribution.Solver.Modular.WeightedPSQ
 import qualified UnitTests.Distribution.Solver.Types.OptionalStanza
+import UnitTests.Options (extraOptions)
 
 main :: IO ()
 main = do
   initTests <- UnitTests.Distribution.Client.Init.tests
-  defaultMain $
+  defaultMainWithIngredients (includingOptions extraOptions : defaultIngredients) $
     testGroup
       "Unit Tests"
       [ testGroup
diff --git a/cabal-install/tests/UnitTests/Distribution/Client/DescribedInstances.hs b/cabal-install/tests/UnitTests/Distribution/Client/DescribedInstances.hs
index 7e52d25173f..a1b34671a04 100644
--- a/cabal-install/tests/UnitTests/Distribution/Client/DescribedInstances.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Client/DescribedInstances.hs
@@ -8,6 +8,7 @@ import Distribution.Client.Compat.Prelude
 import Data.List ((\\))
 import Distribution.Described
 
+import Distribution.Types.Dependency (PrivateAlias)
 import Distribution.Types.PackageId (PackageIdentifier)
 import Distribution.Types.PackageName (PackageName)
 import Distribution.Types.VersionRange (VersionRange)
@@ -164,6 +165,7 @@ instance Described UserConstraint where
         REUnion
           [ "any." <> describePN
           , "setup." <> describePN
+          , "private." <> describePN <> "." <> describe (Proxy :: Proxy PrivateAlias) <> ":" <> describePN
           , describePN
           , describePN <> ":setup." <> describePN
           ]
diff --git a/cabal-install/tests/UnitTests/Distribution/Client/Init/Utils.hs b/cabal-install/tests/UnitTests/Distribution/Client/Init/Utils.hs
index e5ed0748a45..6991613a515 100644
--- a/cabal-install/tests/UnitTests/Distribution/Client/Init/Utils.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Client/Init/Utils.hs
@@ -78,12 +78,12 @@ mkLicense :: SPDX.LicenseId -> SPDX.License
 mkLicense lid = SPDX.License (SPDX.ELicense (SPDX.ELicenseId lid) Nothing)
 
 mangleBaseDep :: a -> (a -> [Dependency]) -> [Dependency]
-mangleBaseDep target f =
-  [ if unPackageName x == "base"
-    then Dependency x anyVersion z
-    else dep
-  | dep@(Dependency x _ z) <- f target
-  ]
+mangleBaseDep target f = map go (f target)
+  where
+    go dep@(Dependency x _ z) =
+      if unPackageName x == "base"
+        then Dependency x anyVersion z
+        else dep
 
 infix 1 @?!, @!?
 
diff --git a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL.hs b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL.hs
index 991c5cafa0e..2dd733416f1 100644
--- a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL.hs
@@ -1,11 +1,12 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 -- | DSL for testing the modular solver
 module UnitTests.Distribution.Solver.Modular.DSL
-  ( ExampleDependency (..)
+  ( ExampleDependency (.., ExAny, ExFix, ExRange, ExSubLibAny, ExSubLibFix, ExFixPriv, ExAnyPriv)
   , Dependencies (..)
   , ExSubLib (..)
   , ExTest (..)
@@ -140,6 +141,7 @@ import Distribution.Solver.Types.Variable
 -------------------------------------------------------------------------------}
 
 type ExamplePkgName = String
+type ExamplePrivateAlias = String
 type ExamplePkgVersion = Int
 type ExamplePkgHash = String -- for example "installed" packages
 type ExampleFlagName = String
@@ -181,18 +183,36 @@ publicDependencies = mempty{depsVisibility = C.LibraryVisibilityPublic}
 unbuildableDependencies :: Dependencies
 unbuildableDependencies = mempty{depsIsBuildable = False}
 
+pattern ExAny :: ExamplePkgName -> ExampleDependency
+pattern ExAny p = ExAnyD Nothing p
+pattern ExFix :: ExamplePkgName -> ExamplePkgVersion -> ExampleDependency
+pattern ExFix p v = ExFixD Nothing p v
+pattern ExRange :: ExamplePkgName -> ExamplePkgVersion -> ExamplePkgVersion -> ExampleDependency
+pattern ExRange p v1 v2 = ExRangeD Nothing p v1 v2
+
+pattern ExSubLibAny :: ExamplePkgName -> ExampleSubLibName -> ExampleDependency
+pattern ExSubLibAny e l = ExSubLibAnyD Nothing e l
+
+pattern ExSubLibFix :: ExamplePkgName -> ExampleSubLibName -> ExamplePkgVersion -> ExampleDependency
+pattern ExSubLibFix e l v = ExSubLibFixD Nothing e l v
+
+pattern ExAnyPriv :: ExamplePrivateAlias -> ExamplePkgName -> ExampleDependency
+pattern ExAnyPriv alias p = ExAnyD (Just alias) p
+pattern ExFixPriv :: ExamplePrivateAlias -> ExamplePkgName -> ExamplePkgVersion -> ExampleDependency
+pattern ExFixPriv alias p v = ExFixD (Just alias) p v
+
 data ExampleDependency
   = -- | Simple dependency on any version
-    ExAny ExamplePkgName
+    ExAnyD (Maybe ExamplePrivateAlias) ExamplePkgName
   | -- | Simple dependency on a fixed version
-    ExFix ExamplePkgName ExamplePkgVersion
+    ExFixD (Maybe ExamplePrivateAlias) ExamplePkgName ExamplePkgVersion
   | -- | Simple dependency on a range of versions, with an inclusive lower bound
     -- and an exclusive upper bound.
-    ExRange ExamplePkgName ExamplePkgVersion ExamplePkgVersion
+    ExRangeD (Maybe ExamplePrivateAlias) ExamplePkgName ExamplePkgVersion ExamplePkgVersion
   | -- | Sub-library dependency
-    ExSubLibAny ExamplePkgName ExampleSubLibName
+    ExSubLibAnyD (Maybe ExamplePrivateAlias) ExamplePkgName ExampleSubLibName
   | -- | Sub-library dependency on a fixed version
-    ExSubLibFix ExamplePkgName ExampleSubLibName ExamplePkgVersion
+    ExSubLibFixD (Maybe ExamplePrivateAlias) ExamplePkgName ExampleSubLibName ExamplePkgVersion
   | -- | Build-tool-depends dependency
     ExBuildToolAny ExamplePkgName ExampleExeName
   | -- | Build-tool-depends dependency on a fixed version
@@ -272,12 +292,10 @@ data ExampleQualifier
   = QualNone
   | QualIndep ExamplePkgName
   | QualSetup ExamplePkgName
-  | -- The two package names are the build target and the package containing the
-    -- setup script.
-    QualIndepSetup ExamplePkgName ExamplePkgName
   | -- The two package names are the package depending on the exe and the
     -- package containing the exe.
     QualExe ExamplePkgName ExamplePkgName
+-- TODO: Add QualPrivateAlias?
 
 -- | Whether to enable tests in all packages in a test case.
 newtype EnableAllTests = EnableAllTests Bool
@@ -390,9 +408,9 @@ exInst pn v hash deps = ExInst pn v hash (map exInstHash deps)
 -- these packages.
 type ExampleDb = [Either ExampleInstalled ExampleAvailable]
 
-type DependencyTree a = C.CondTree C.ConfVar [C.Dependency] a
+type DependencyTree a = C.CondTree C.ConfVar C.Dependencies a
 
-type DependencyComponent a = C.CondBranch C.ConfVar [C.Dependency] a
+type DependencyComponent a = C.CondBranch C.ConfVar C.Dependencies a
 
 exDbPkgs :: ExampleDb -> [ExamplePkgName]
 exDbPkgs = map (either exInstName exAvName)
@@ -589,11 +607,11 @@ exAvSrcPkg ex =
     extractFlags deps = concatMap go (depsExampleDependencies deps)
       where
         go :: ExampleDependency -> [ExampleFlagName]
-        go (ExAny _) = []
-        go (ExFix _ _) = []
-        go (ExRange _ _ _) = []
-        go (ExSubLibAny _ _) = []
-        go (ExSubLibFix _ _ _) = []
+        go (ExAnyD{}) = []
+        go (ExFixD{}) = []
+        go (ExRangeD{}) = []
+        go (ExSubLibAnyD{}) = []
+        go (ExSubLibFixD{}) = []
         go (ExBuildToolAny _ _) = []
         go (ExBuildToolFix _ _ _) = []
         go (ExLegacyBuildToolAny _) = []
@@ -622,7 +640,8 @@ exAvSrcPkg ex =
     mkCondTree :: (C.LibraryVisibility -> C.BuildInfo -> a) -> Dependencies -> DependencyTree a
     mkCondTree mkComponent deps =
       let (libraryDeps, exts, mlang, pcpkgs, buildTools, legacyBuildTools) = splitTopLevel (depsExampleDependencies deps)
-          (directDeps, flaggedDeps) = splitDeps libraryDeps
+          (allDirectDeps, flaggedDeps) = splitDeps libraryDeps
+          (privateDeps, directDeps) = partition (\(_, _, _, is_private) -> isJust is_private) allDirectDeps
           component = mkComponent (depsVisibility deps) bi
           bi =
             mempty
@@ -649,12 +668,20 @@ exAvSrcPkg ex =
             , -- TODO: Arguably, build-tools dependencies should also
               -- effect constraints on conditional tree. But no way to
               -- distinguish between them
-              C.condTreeConstraints = map mkDirect directDeps
+              C.condTreeConstraints =
+                mempty
+                  { C.publicDependencies = map mkDirect directDeps
+                  , C.privateDependencies = map mkDirectD privateDeps
+                  }
             , C.condTreeComponents = map (mkFlagged mkComponent) flaggedDeps
             }
 
-    mkDirect :: (ExamplePkgName, C.LibraryName, C.VersionRange) -> C.Dependency
-    mkDirect (dep, name, vr) = C.Dependency (C.mkPackageName dep) vr (NonEmptySet.singleton name)
+    mkDirect :: (ExamplePkgName, C.LibraryName, C.VersionRange, Maybe ExamplePrivateAlias) -> C.Dependency
+    mkDirect (dep, name, vr, _) = C.Dependency (C.mkPackageName dep) vr (NonEmptySet.singleton name)
+
+    mkDirectD :: (ExamplePkgName, C.LibraryName, C.VersionRange, Maybe ExamplePrivateAlias) -> C.PrivateDependency
+    mkDirectD (dep, name, vr, Just alias) = C.PrivateDependency (C.PrivateAlias (fromString alias)) [C.Dependency (C.mkPackageName dep) vr (NonEmptySet.singleton name)]
+    mkDirectD (_, _, _, Nothing) = error "mkDirectD: private deps are never Nothing since we partition them by 'isJust' above"
 
     mkFlagged
       :: (C.LibraryVisibility -> C.BuildInfo -> a)
@@ -673,26 +700,26 @@ exAvSrcPkg ex =
     -- guarded by a flag.
     splitDeps
       :: [ExampleDependency]
-      -> ( [(ExamplePkgName, C.LibraryName, C.VersionRange)]
+      -> ( [(ExamplePkgName, C.LibraryName, C.VersionRange, Maybe ExamplePrivateAlias)]
          , [(ExampleFlagName, Dependencies, Dependencies)]
          )
     splitDeps [] =
       ([], [])
-    splitDeps (ExAny p : deps) =
+    splitDeps (ExAnyD is_priv p : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
-       in ((p, C.LMainLibName, C.anyVersion) : directDeps, flaggedDeps)
-    splitDeps (ExFix p v : deps) =
+       in ((p, C.LMainLibName, C.anyVersion, is_priv) : directDeps, flaggedDeps)
+    splitDeps (ExFixD is_priv p v : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
-       in ((p, C.LMainLibName, C.thisVersion $ mkSimpleVersion v) : directDeps, flaggedDeps)
-    splitDeps (ExRange p v1 v2 : deps) =
+       in ((p, C.LMainLibName, C.thisVersion $ mkSimpleVersion v, is_priv) : directDeps, flaggedDeps)
+    splitDeps (ExRangeD is_priv p v1 v2 : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
-       in ((p, C.LMainLibName, mkVersionRange v1 v2) : directDeps, flaggedDeps)
-    splitDeps (ExSubLibAny p lib : deps) =
+       in ((p, C.LMainLibName, mkVersionRange v1 v2, is_priv) : directDeps, flaggedDeps)
+    splitDeps (ExSubLibAnyD is_priv p lib : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
-       in ((p, C.LSubLibName (C.mkUnqualComponentName lib), C.anyVersion) : directDeps, flaggedDeps)
-    splitDeps (ExSubLibFix p lib v : deps) =
+       in ((p, C.LSubLibName (C.mkUnqualComponentName lib), C.anyVersion, is_priv) : directDeps, flaggedDeps)
+    splitDeps (ExSubLibFixD is_priv p lib v : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
-       in ((p, C.LSubLibName (C.mkUnqualComponentName lib), C.thisVersion $ mkSimpleVersion v) : directDeps, flaggedDeps)
+       in ((p, C.LSubLibName (C.mkUnqualComponentName lib), C.thisVersion $ mkSimpleVersion v, is_priv) : directDeps, flaggedDeps)
     splitDeps (ExFlagged f a b : deps) =
       let (directDeps, flaggedDeps) = splitDeps deps
        in (directDeps, (f, a, b) : flaggedDeps)
@@ -702,7 +729,10 @@ exAvSrcPkg ex =
     mkSetupDeps :: [ExampleDependency] -> [C.Dependency]
     mkSetupDeps deps =
       case splitDeps deps of
-        (directDeps, []) -> map mkDirect directDeps
+        (directDeps, []) ->
+          if any (\(_, _, _, p) -> isJust p) directDeps
+            then error "mkSetupDeps: custom setup has private deps"
+            else map mkDirect directDeps
         _ -> error "mkSetupDeps: custom setup has non-simple deps"
 
     -- Check for `UnknownLanguages` and `UnknownExtensions`. See
@@ -844,7 +874,7 @@ exResolve
             fmap
               ( \p ->
                   PackageConstraint
-                    (scopeToplevel (C.mkPackageName p))
+                    (ScopeAnyQualifier (C.mkPackageName p))
                     (PackagePropertyStanzas [TestStanzas])
               )
               (exDbPkgs db)
diff --git a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs
index 91ec541f976..6bec16ea5e1 100644
--- a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs
@@ -18,6 +18,7 @@ module UnitTests.Distribution.Solver.Modular.DSL.TestCaseUtils
   , preferences
   , setVerbose
   , enableAllTests
+  , solverResult
   , solverSuccess
   , solverFailure
   , anySolverFailure
@@ -46,6 +47,7 @@ import Language.Haskell.Extension (Extension (..), Language (..))
 -- cabal-install
 
 import Distribution.Client.Dependency (foldProgress)
+import qualified Distribution.Solver.Types.ComponentDeps as C
 import qualified Distribution.Solver.Types.PackagePath as P
 import Distribution.Solver.Types.PkgConfigDb (PkgConfigDb (..), pkgConfigDbFromList)
 import Distribution.Solver.Types.Settings
@@ -144,6 +146,9 @@ data SolverResult = SolverResult
   -- the given plan.
   }
 
+solverResult :: ([String] -> Bool) -> [(String, Int)] -> SolverResult
+solverResult slog r = SolverResult slog (Right r)
+
 solverSuccess :: [(String, Int)] -> SolverResult
 solverSuccess = SolverResult (const True) . Right
 
@@ -314,13 +319,9 @@ runTest SolverTest{..} = askOption $ \(OptionShowSolverLog showSolverLog) ->
               P.QualToplevel
           QualSetup s ->
             P.PackagePath
-              P.DefaultNamespace
-              (P.QualSetup (C.mkPackageName s))
-          QualIndepSetup p s ->
-            P.PackagePath
-              (P.Independent $ C.mkPackageName p)
-              (P.QualSetup (C.mkPackageName s))
+              (P.IndependentComponent (C.mkPackageName s) C.ComponentSetup)
+              (P.QualToplevel)
           QualExe p1 p2 ->
             P.PackagePath
-              P.DefaultNamespace
-              (P.QualExe (C.mkPackageName p1) (C.mkPackageName p2))
+              (P.IndependentBuildTool (C.mkPackageName p1) (C.mkPackageName p2))
+              P.QualToplevel
diff --git a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/QuickCheck.hs b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/QuickCheck.hs
index 114db775f21..7fcd6107ddf 100644
--- a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/QuickCheck.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/QuickCheck.hs
@@ -24,6 +24,8 @@ import Distribution.Utils.ShortText (ShortText)
 
 import Distribution.Client.Setup (defaultMaxBackjumps)
 
+import Distribution.ModuleName
+import Distribution.Types.Dependency (PrivateAlias (..))
 import Distribution.Types.LibraryVisibility
 import Distribution.Types.PackageName
 import Distribution.Types.UnqualComponentName
@@ -34,6 +36,7 @@ import Distribution.Solver.Types.ComponentDeps
   , ComponentDeps
   )
 import qualified Distribution.Solver.Types.ComponentDeps as CD
+import qualified Distribution.Solver.Types.ComponentDeps as P
 import Distribution.Solver.Types.OptionalStanza
 import Distribution.Solver.Types.PackageConstraint
 import qualified Distribution.Solver.Types.PackagePath as P
@@ -75,7 +78,8 @@ tests =
               ReverseOrder -> reverse targets
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                isRight (resultPlan r1) === isRight (resultPlan r2)
+                isRight (resultPlan r1)
+                  === isRight (resultPlan r2)
   , testPropertyWithSeed
       "solvable without --independent-goals => solvable with --independent-goals"
       $ \test reorderGoals ->
@@ -92,7 +96,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                isRight (resultPlan r1) `implies` isRight (resultPlan r2)
+                isRight (resultPlan r1)
+                  `implies` isRight (resultPlan r2)
   , testPropertyWithSeed "backjumping does not affect solvability" $
       \test reorderGoals indepGoals ->
         let r1 = solve' (EnableBackjumping True) test
@@ -108,7 +113,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                isRight (resultPlan r1) === isRight (resultPlan r2)
+                isRight (resultPlan r1)
+                  === isRight (resultPlan r2)
   , testPropertyWithSeed "fine-grained conflicts does not affect solvability" $
       \test reorderGoals indepGoals ->
         let r1 = solve' (FineGrainedConflicts True) test
@@ -124,7 +130,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                isRight (resultPlan r1) === isRight (resultPlan r2)
+                isRight (resultPlan r1)
+                  === isRight (resultPlan r2)
   , testPropertyWithSeed "prefer oldest does not affect solvability" $
       \test reorderGoals indepGoals ->
         let r1 = solve' (PreferOldest True) test
@@ -140,7 +147,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                isRight (resultPlan r1) === isRight (resultPlan r2)
+                isRight (resultPlan r1)
+                  === isRight (resultPlan r2)
   , -- The next two tests use --no-count-conflicts, because the goal order used
     -- with --count-conflicts depends on the total set of conflicts seen by the
     -- solver. The solver explores more of the tree and encounters more
@@ -165,7 +173,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                resultPlan r1 === resultPlan r2
+                resultPlan r1
+                  === resultPlan r2
   , testPropertyWithSeed
       "fine-grained conflicts does not affect the result (with static goal order)"
       $ \test reorderGoals indepGoals ->
@@ -182,7 +191,8 @@ tests =
                 Nothing
          in counterexample (showResults r1 r2) $
               noneReachedBackjumpLimit [r1, r2] ==>
-                resultPlan r1 === resultPlan r2
+                resultPlan r1
+                  === resultPlan r2
   ]
   where
     noneReachedBackjumpLimit :: [Result] -> Bool
@@ -612,10 +622,14 @@ instance Hashable a => Hashable (P.Qualified a)
 instance Hashable P.PackagePath
 instance Hashable P.Qualifier
 instance Hashable P.Namespace
+instance Hashable P.Component
+instance Hashable UnqualComponentName
 instance Hashable OptionalStanza
 instance Hashable FlagName
 instance Hashable PackageName
 instance Hashable ShortText
+instance Hashable ModuleName
+instance Hashable PrivateAlias
 
 deriving instance Generic (Variable pn)
 deriving instance Generic (P.Qualified a)
diff --git a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs
index d32bc85dc15..9dd20fc82ac 100644
--- a/cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs
@@ -23,6 +23,8 @@ import Language.Haskell.Extension
   )
 
 -- cabal-install
+
+import qualified Distribution.Solver.Types.ComponentDeps as P
 import Distribution.Solver.Types.Flag
 import Distribution.Solver.Types.OptionalStanza
 import Distribution.Solver.Types.PackageConstraint
@@ -92,7 +94,7 @@ tests =
   , testGroup
       "Qualified manual flag constraints"
       [ let name = "Top-level flag constraint does not constrain setup dep's flag"
-            cs = [ExFlagConstraint (ScopeQualified P.QualToplevel "B") "flag" False]
+            cs = [ExFlagConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "B") "flag" False]
          in runTest $
               constraints cs $
                 mkTest dbSetupDepWithManualFlag name ["A"] $
@@ -105,7 +107,7 @@ tests =
                     ]
       , let name = "Solver can toggle setup dep's flag to match top-level constraint"
             cs =
-              [ ExFlagConstraint (ScopeQualified P.QualToplevel "B") "flag" False
+              [ ExFlagConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "B") "flag" False
               , ExVersionConstraint (ScopeAnyQualifier "b-2-true-dep") V.noVersion
               ]
          in runTest $
@@ -120,8 +122,8 @@ tests =
                     ]
       , let name = "User can constrain flags separately with qualified constraints"
             cs =
-              [ ExFlagConstraint (ScopeQualified P.QualToplevel "B") "flag" True
-              , ExFlagConstraint (ScopeQualified (P.QualSetup "A") "B") "flag" False
+              [ ExFlagConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "B") "flag" True
+              , ExFlagConstraint (ScopeQualified (P.IndependentComponent "A" P.ComponentSetup) P.QualToplevel "B") "flag" False
               ]
          in runTest $
               constraints cs $
@@ -135,15 +137,15 @@ tests =
                     ]
       , -- Regression test for #4299
         let name = "Solver can link deps when only one has constrained manual flag"
-            cs = [ExFlagConstraint (ScopeQualified P.QualToplevel "B") "flag" False]
+            cs = [ExFlagConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "B") "flag" False]
          in runTest $
               constraints cs $
                 mkTest dbLinkedSetupDepWithManualFlag name ["A"] $
                   solverSuccess [("A", 1), ("B", 1), ("b-1-false-dep", 1)]
       , let name = "Solver cannot link deps that have conflicting manual flag constraints"
             cs =
-              [ ExFlagConstraint (ScopeQualified P.QualToplevel "B") "flag" True
-              , ExFlagConstraint (ScopeQualified (P.QualSetup "A") "B") "flag" False
+              [ ExFlagConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "B") "flag" True
+              , ExFlagConstraint (ScopeQualified (P.IndependentComponent "A" P.ComponentSetup) P.QualToplevel "B") "flag" False
               ]
             failureReason = "(constraint from unknown source requires opposite flag selection)"
             checkFullLog lns =
@@ -279,8 +281,8 @@ tests =
                 mkTest dbConstraints "force older versions with unqualified constraint" ["A", "B", "C"] $
                   solverSuccess [("A", 1), ("B", 2), ("C", 3), ("D", 1), ("D", 2), ("D", 3)]
       , let cs =
-              [ ExVersionConstraint (ScopeQualified P.QualToplevel "D") $ mkVersionRange 1 4
-              , ExVersionConstraint (ScopeQualified (P.QualSetup "B") "D") $ mkVersionRange 4 7
+              [ ExVersionConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "D") $ mkVersionRange 1 4
+              , ExVersionConstraint (ScopeQualified (P.IndependentComponent "B" P.ComponentSetup) P.QualToplevel "D") $ mkVersionRange 4 7
               ]
          in runTest $
               constraints cs $
@@ -363,7 +365,7 @@ tests =
       , runTest $ testIndepGoals5 "indepGoals5 - default goal order" DefaultGoalOrder
       , runTest $ testIndepGoals6 "indepGoals6 - fixed goal order" FixedGoalOrder
       , runTest $ testIndepGoals6 "indepGoals6 - default goal order" DefaultGoalOrder
-      , expectFailBecause "#9466" $ runTest $ testIndepGoals7 "indepGoals7"
+      , runTest $ testIndepGoals7 "indepGoals7"
       , runTest $ testIndepGoals8 "indepGoals8"
       ]
   , -- Tests designed for the backjumping blog post
@@ -517,6 +519,7 @@ tests =
                   ++ "[__1] rejecting: H:bt-pkg:exe.bt-pkg-2.0.0 (conflict: H => H:bt-pkg:exe.bt-pkg (exe exe1)==3.0.0)"
       , runTest $ chooseExeAfterBuildToolsPackage True "choose exe after choosing its package - success"
       , runTest $ chooseExeAfterBuildToolsPackage False "choose exe after choosing its package - failure"
+      , runTest $ needTwoBuildToolPkgVersions "needs two build-tool-pkg versions"
       , runTest $ rejectInstalledBuildToolPackage "reject installed package for build-tool dependency"
       , runTest $ requireConsistentBuildToolVersions "build tool versions must be consistent within one package"
       ]
@@ -859,6 +862,26 @@ tests =
                     SolverResult (isInfixOf msg) $
                       Right [("A", 1), ("B", 1)]
       ]
+  , testGroup
+      "Private dependencies"
+      [ runTest privDep1
+      , runTest privDep2
+      , runTest privDep3
+      , runTest privDep4
+      , runTest privDep5
+      , runTest privDep6
+      , runTest privDep7
+      , runTest privDep7a
+      , runTest privDep8
+      , runTest privDep8a
+      , runTest privDep9
+      , runTest privDep10
+      , runTest privDep11
+      , runTest privDep12
+      , runTest privDep13
+      , runTest privDep14
+      , runTest privDep15
+      ]
   , -- Tests for the contents of the solver's log
     testGroup
       "Solver log"
@@ -2366,6 +2389,20 @@ dbBuildTools =
   , Right $ exAv "bt-pkg" 1 []
   ]
 
+needTwoBuildToolPkgVersions :: String -> SolverTest
+needTwoBuildToolPkgVersions name = setVerbose $ mkTest db name ["A"] (solverSuccess [("A", 1), ("build-tool-pkg", 1), ("build-tool-pkg", 2)])
+  where
+    db :: ExampleDb
+    db =
+      [ Right $ exAv "build-tool-pkg" 1 [] `withExe` exExe "build-tool-exe" []
+      , Right $ exAv "build-tool-pkg" 2 [] `withExe` exExe "build-tool-exe" []
+      , Right $
+          exAvNoLibrary "A" 1
+            `withExe` exExe
+              "my-exe"
+              [ExFix "build-tool-pkg" 1, ExBuildToolFix "build-tool-pkg" "build-tool-exe" 2]
+      ]
+
 -- The solver should never choose an installed package for a build tool
 -- dependency.
 rejectInstalledBuildToolPackage :: String -> SolverTest
@@ -2583,6 +2620,232 @@ setupStanzaTest2 =
       ["A"]
       (solverFailure ("unknown package: A:setup.C (dependency of A:setup.B *test)" `isInfixOf`))
 
+--
+-- Private Dependency tests
+
+-- Test 1: A and B can choose different versions of C because C is a private dependency of A
+priv_db1 :: ExampleDb
+priv_db1 =
+  [ Left $ exInst "C" 1 "C-1" []
+  , Left $ exInst "C" 2 "C-2" []
+  , Right $ exAv "A" 1 [ExFixPriv "G0" "C" 1]
+  , Right $ exAv "B" 1 [ExFix "C" 2]
+  , Right $ exAv "D" 1 [ExAny "A", ExAny "B"]
+  ]
+
+privDep1 :: SolverTest
+privDep1 = setVerbose $ mkTest priv_db1 "private-dependencies-1" ["D"] (solverSuccess [("A", 1), ("B", 1), ("D", 1)])
+
+-- Test 2: A depends on both C publically and privately, directly
+priv_db2 :: ExampleDb
+priv_db2 =
+  [ Left $ exInst "C" 1 "C-1" []
+  , Right $ exAv "A" 1 [ExFix "C" 1, ExFixPriv "G0" "C" 1]
+  ]
+
+privDep2 :: SolverTest
+privDep2 = setVerbose $ mkTest priv_db2 "private-dependencies-2" ["A"] (solverSuccess [("A", 1)])
+
+-- Test 3: A depends on both C publically and privately, transitively
+priv_db3 :: ExampleDb
+priv_db3 =
+  [ Left $ exInst "C" 1 "C-1" []
+  , Right $ exAv "D" 1 [ExFix "C" 1]
+  , Right $ exAv "A" 1 [ExFix "D" 1, ExFixPriv "G0" "C" 1]
+  ]
+
+privDep3 :: SolverTest
+privDep3 = setVerbose $ mkTest priv_db3 "private-dependencies-3" ["A"] (solverSuccess [("A", 1), ("D", 1)])
+
+-- Test 4: Private dependency do not apply transitively, so we fail because the
+-- version of E must match
+priv_db4 :: ExampleDb
+priv_db4 =
+  [ Left $ exInst "E" 1 "E-1" []
+  , Left $ exInst "E" 2 "E-2" []
+  , Right $ exAv "C" 1 [ExFix "E" 1]
+  , Right $ exAv "C" 2 [ExFix "E" 2]
+  , Right $ exAv "A" 1 [ExFixPriv "G0" "C" 1]
+  , Right $ exAv "B" 1 [ExFix "C" 2]
+  , Right $ exAv "D" 1 [ExAny "A", ExAny "B"]
+  ]
+
+privDep4 :: SolverTest
+privDep4 = setVerbose $ mkTest priv_db4 "private-dependencies-4" ["D"] (solverFailure ("(conflict: E==2.0.0/installed-2, A:lib:G0.C => E==1.0.0)" `isInfixOf`))
+
+-- Test 5: Private dependencies and setup dependencies can choose different versions
+
+priv_db5 :: ExampleDb
+priv_db5 =
+  [ Left $ exInst "E" 1 "E-1" []
+  , Left $ exInst "E" 2 "E-2" []
+  , Right $ exAv "A" 1 [ExFixPriv "G0" "E" 1] `withSetupDeps` [ExFix "E" 2]
+  ]
+
+privDep5 :: SolverTest
+privDep5 = setVerbose $ mkTest priv_db5 "private-dependencies-5" ["A"] (solverSuccess [("A", 1)])
+
+-- Private scope, with two dependencies
+priv_db6 :: ExampleDb
+priv_db6 =
+  let f1 = exInst "F" 1 "F-1" []
+      f2 = exInst "F" 2 "F-2" []
+   in [ Left $ exInst "E" 1 "E-1" [f1]
+      , Left $ exInst "E" 2 "E-2" [f2]
+      , Left f1
+      , Left f2
+      , Right $ exAv "A" 1 [ExFix "E" 2, ExFixPriv "G0" "E" 1, ExAnyPriv "G0" "F"]
+      ]
+
+privDep6 :: SolverTest
+privDep6 = setVerbose $ mkTest priv_db6 "private-dependencies-6" ["A"] (solverSuccess [("A", 1)])
+
+-- A dependency structure which violates the closure property for private dependency scopes
+priv_db7 :: ExampleDb
+priv_db7 =
+  [ Right $ exAv "A" 1 [ExAny "B"]
+  , Right $ exAv "B" 1 [ExAny "C"]
+  , Right $ exAv "C" 1 []
+  , Right $ exAv "P" 1 [ExFixPriv "G0" "A" 1, ExAnyPriv "G0" "C"]
+  ]
+
+privDep7 :: SolverTest
+privDep7 = setVerbose $ mkTest priv_db7 "private-dependencies-7" ["P"] (solverFailure ("private scopes must contain its closure, but package B is not included in the private scope P:lib:G0." `isInfixOf`))
+
+-- Closure property with external deps
+priv_db7a :: ExampleDb
+priv_db7a =
+  let a = exInst "A" 1 "A-1" [b]
+      b = exInst "B" 1 "B-1" [c]
+      c = exInst "C" 1 "C-1" []
+   in [ Left a
+      , Left b
+      , Left c
+      , Right $ exAv "P" 1 [ExFixPriv "G0" "A" 1, ExAnyPriv "G0" "C"]
+      ]
+
+privDep7a :: SolverTest
+privDep7a = setVerbose $ mkTest priv_db7a "private-dependencies-7a" ["P"] (solverFailure ("private scopes must contain its closure, but package B is not included in the private scope P:lib:G0." `isInfixOf`))
+
+priv_db8 :: ExampleDb
+priv_db8 =
+  [ Right $ exAv "A" 1 [ExAny "B"]
+  , Right $ exAv "B" 1 [ExAny "C"]
+  , Right $ exAv "C" 1 []
+  , Right $ exAv "P" 1 [ExFixPriv "G0" "A" 1, ExAnyPriv "G0" "B", ExAnyPriv "G0" "C"]
+  ]
+
+privDep8 :: SolverTest
+privDep8 = setVerbose $ mkTest priv_db8 "private-dependencies-8" ["P"] (solverSuccess [("A", 1), ("B", 1), ("C", 1), ("P", 1)])
+
+priv_db8a :: ExampleDb
+priv_db8a =
+  let a = exInst "A" 1 "A-1" [b]
+      b = exInst "B" 1 "B-1" [c]
+      c = exInst "C" 1 "C-1" []
+   in [ Left a
+      , Left b
+      , Left c
+      , Right $ exAv "P" 1 [ExFixPriv "G0" "A" 1, ExAnyPriv "G0" "B", ExAnyPriv "G0" "C"]
+      ]
+
+privDep8a :: SolverTest
+privDep8a = setVerbose $ mkTest priv_db8a "private-dependencies-8a" ["P"] (solverSuccess [("P", 1)])
+
+-- Two different private scopes can have two different versions
+priv_db9 :: ExampleDb
+priv_db9 =
+  let a = exInst "A" 1 "A-1" []
+      b = exInst "A" 2 "A-2" []
+   in [ Left a
+      , Left b
+      , Right $ exAv "P" 1 [ExFixPriv "G0" "A" 1, ExFixPriv "G1" "A" 2]
+      ]
+
+privDep9 :: SolverTest
+privDep9 = setVerbose $ mkTest priv_db9 "private-dependencies-9" ["P"] (solverSuccess [("P", 1)])
+
+-- Backtrack when closure property is violated
+priv_db10 :: ExampleDb
+priv_db10 =
+  let a2 = exInst "A" 2 "A-2" [b]
+      a1 = exInst "A" 1 "A-1" []
+      b = exInst "B" 1 "B-1" [c]
+      c = exInst "C" 1 "C-1" []
+   in [ Left a1
+      , Left a2
+      , Left b
+      , Left c
+      , Right $ exAv "P" 1 [ExAnyPriv "G0" "A", ExAnyPriv "G0" "C"]
+      ]
+
+privDep10 :: SolverTest
+privDep10 =
+  setVerbose $
+    mkTest
+      priv_db10
+      "private-dependencies-10"
+      ["P"]
+      (solverResult (any ("private scopes must contain its closure, but package B is not included in the private scope P:lib:G0." `isInfixOf`)) [("P", 1)])
+
+-- Testing constraints DON'T apply to private dependencies
+priv_db11 :: ExampleDb
+priv_db11 =
+  [ Left (exInst "A" 1 "A-1" [])
+  , Right $ exAv "P" 1 [ExAnyPriv "G0" "A"]
+  ]
+
+privDep11 :: SolverTest
+privDep11 =
+  setVerbose $
+    constraints [ExVersionConstraint (ScopeQualified P.DefaultNamespace P.QualToplevel "A") (V.thisVersion (V.mkVersion [2]))] $
+      mkTest priv_db11 "private-dependencies-11" ["P"] (solverSuccess [("P", 1)])
+
+-- Testing suitably scoped constraints do apply to private dependencies
+privDep12 :: SolverTest
+privDep12 =
+  setVerbose $
+    constraints [ExVersionConstraint (ScopePrivate "P" "G0" "A") (V.thisVersion (V.mkVersion [2]))] $
+      mkTest priv_db11 "private-dependencies-12" ["P"] (solverFailure ("constraint from unknown source requires ==2" `isInfixOf`))
+
+-- Testing that `any` qualifier applies to private deps
+privDep13 :: SolverTest
+privDep13 =
+  setVerbose $
+    constraints [ExVersionConstraint (ScopeAnyQualifier "A") (V.thisVersion (V.mkVersion [2]))] $
+      mkTest priv_db11 "private-dependencies-13" ["P"] (solverFailure ("constraint from unknown source requires ==2" `isInfixOf`))
+
+-- Testing nested private scopes
+priv_db14 :: ExampleDb
+priv_db14 =
+  priv_db6 -- uses A depends on E, F pkg names.
+    ++ [ Left $ exInst "B" 1 "B-1" []
+       , Right $ exAv "P" 1 [ExAnyPriv "G0" "A", ExAnyPriv "G0" "B"]
+       ]
+
+privDep14 :: SolverTest
+privDep14 =
+  setVerbose $
+    mkTest priv_db14 "private-dependencies-14" ["P"] (solverSuccess [("A", 1), ("P", 1)])
+
+-- Testing nested private scopes, where outer private scope includes deps of nested private scope.
+priv_db15 :: ExampleDb
+priv_db15 =
+  let f1 = exInst "F" 1 "F-1" []
+      f2 = exInst "F" 2 "F-2" []
+   in [ Left $ exInst "E" 1 "E-1" [f1]
+      , Left $ exInst "E" 2 "E-2" [f2]
+      , Left f1
+      , Left f2
+      , Right $ exAv "A" 1 [ExFix "E" 2, ExFixPriv "G0" "E" 1, ExAnyPriv "G0" "F"]
+      , Right $ exAv "P" 1 [ExAnyPriv "G0" "A", ExAnyPriv "G0" "E"]
+      ]
+
+privDep15 :: SolverTest
+privDep15 =
+  setVerbose $
+    mkTest priv_db15 "private-dependencies-15" ["P"] (solverSuccess [("A", 1), ("P", 1)])
+
 -- | Returns true if the second list contains all elements of the first list, in
 -- order.
 containsInOrder :: Eq a => [a] -> [a] -> Bool
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/README.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/README.md
new file mode 100644
index 00000000000..bc40cd6f9a5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/README.md
@@ -0,0 +1,10 @@
+Proof of concept for Cabal hooks compatability scheme, which tests private
+dependencies
+
+* `lib01` - The library which defines the hooks interface, which can have different versions.
+
+* `main-prog` - A program written against the `lib01` interface, but needs to work with multiple versions.
+
+* `hooks-exe` - The executable which can be compiled against multiple versions of `lib01`.
+
+* `hooks-lib` - A compability library which depends on all versions of lib01 which are supported and provides conversions between the new and old datatypes.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.project b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.project
new file mode 100644
index 00000000000..e25e053a3c0
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.project
@@ -0,0 +1 @@
+packages: hooks-exe hooks-lib main-prog
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.test.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.test.hs
new file mode 100644
index 00000000000..de74350e18a
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/cabal.test.hs
@@ -0,0 +1,20 @@
+import Test.Cabal.Prelude
+
+main =
+  cabalTest $ recordMode DoNotRecord $
+    withProjectFile "cabal.project" $
+      withRepo "repo" $ do
+        cabal "build" ["exe:hooks-exe", "--constraint=private.hooks-exe.L01:lib01 == 0.1.0.0"]
+        exePath <- withPlan $ planExePath "hooks-exe" "hooks-exe"
+        out1 <- cabal' "run" ["exe:main-prog", "--", exePath]
+
+        assertOutputContains "0.1.0.0" out1
+        assertOutputContains "hooks_show: A" out1
+        assertOutputContains "hooks_inc: B" out1
+
+        cabal "build" ["exe:hooks-exe", "--constraint=private.hooks-exe.L01:lib01 == 0.2.0.0"]
+        out2 <- cabal' "run" ["exe:main-prog", "--", exePath]
+
+        assertOutputContains "0.2.0.0" out2
+        assertOutputContains "hooks_show: A {value = 5}" out2
+        assertOutputContains "hooks_inc: B" out2
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/CHANGELOG.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/CHANGELOG.md
new file mode 100644
index 00000000000..ae45e4d0b14
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for hooks-exe
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/app/Main.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/app/Main.hs
new file mode 100644
index 00000000000..38dc9f85525
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/app/Main.hs
@@ -0,0 +1,35 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP #-}
+module Main where
+
+import System.Environment
+
+import Prelude hiding (getContents, putStr, hPutStr)
+import Data.ByteString.Lazy (getContents, putStr, hPutStr)
+import System.Environment (getArgs)
+import System.IO (stderr, hPrint)
+import Data.String
+import Data.Binary
+import L01.Lib
+
+-- | Create an executable which accepts the name of a hook as the argument,
+-- then reads arguments to the hook over stdin and writes the results of the hook
+-- to stdout.
+main :: IO ()
+main = do
+  [hookName] <- getArgs
+  case hookName of
+   "version" -> do
+    putStr $ encode (VERSION_lib01 :: String)
+   "show" -> do
+      s <- getContents
+      let a1 :: A = decode s
+          res = show a1
+      putStr (encode res)
+   "inc" -> do
+      s <- getContents
+      let a1 :: A = decode s
+          res = inc a1
+      putStr (encode res)
+   _ -> error "Hook not yet implemented"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/hooks-exe.cabal b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/hooks-exe.cabal
new file mode 100644
index 00000000000..b03865b863a
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-exe/hooks-exe.cabal
@@ -0,0 +1,19 @@
+cabal-version:   3.0
+name:            hooks-exe
+version:         0.1.0.0
+license:         NONE
+author:          matthewtpickering@gmail.com
+maintainer:      Matthew Pickering
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+executable hooks-exe
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    base, bytestring, binary, directory
+    private-build-depends: L01 with (lib01)
+    hs-source-dirs:   app
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/CHANGELOG.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/CHANGELOG.md
new file mode 100644
index 00000000000..85a864adeca
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for hooks-lib
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/hooks-lib.cabal b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/hooks-lib.cabal
new file mode 100644
index 00000000000..bb5efe62961
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/hooks-lib.cabal
@@ -0,0 +1,20 @@
+cabal-version:   3.0
+name:            hooks-lib
+version:         0.1.0.0
+license:         NONE
+author:          matthewtpickering@gmail.com
+maintainer:      Matthew Pickering
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  HooksLib
+    build-depends:    base, lib01 == 0.2.0.0,  mtl, process, binary, bytestring, deepseq
+    private-build-depends: V01 with (lib01 == 0.1.0.0), V02 with (lib01 == 0.2.0.0)
+    hs-source-dirs:   src
+    default-language: Haskell2010
+
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/HooksLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/HooksLib.hs
new file mode 100644
index 00000000000..aae813b46f5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/HooksLib.hs
@@ -0,0 +1,133 @@
+{-# LANGUAGE PackageImports #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+module HooksLib where
+
+import Control.Monad.Reader
+
+import V01.Lib as L1
+import V02.Lib as L2
+import "lib01" Lib as L
+
+import System.IO (stderr)
+import System.Process
+import Control.Exception as C
+import Data.Binary
+import Control.Concurrent
+import GHC.IO.Handle (BufferMode(..), hClose, hSetBuffering)
+import Control.Concurrent.MVar
+import Control.Concurrent
+import qualified Control.Exception as C
+import Data.ByteString.Lazy (hPutStr, hGetContents)
+import qualified Data.ByteString.Char8 as C8
+import Control.DeepSeq
+import GHC.IO.Exception as GHC
+import Foreign.C.Error
+
+data SupportedVersion = V01 | V02
+
+--import Lib as LX
+
+data HooksEnv = HooksEnv { hooksExe :: FilePath,  hooksVersion :: SupportedVersion }
+
+type HooksM a = ReaderT HooksEnv IO a
+
+version :: FilePath -> IO (Maybe SupportedVersion)
+version fp = do
+  (ver :: String) <- readHooksExe_ fp "version" ()
+  print ver
+  return $ case C8.split '.' (C8.pack ver) of
+    ["0","1","0","0"] -> Just V01
+    ["0","2","0","0"] -> Just V02
+    _ -> Nothing
+
+withHooksExe :: FilePath -> HooksM a -> IO a
+withHooksExe prog action = do
+  ver <- version prog
+  case ver of
+    Just sver -> runReaderT action (HooksEnv prog sver)
+    Nothing -> error "Hooks executable is unsupported version"
+
+convertA1 :: L.A -> L1.A
+convertA1 (L.A {}) = L1.A
+convertA1 (L.B) = L1.B
+
+convertA2 :: L.A -> L2.A
+convertA2 (L.A x) = (L2.A x)
+convertA2 L.B = L2.B
+
+revertA1 :: L1.A -> L.A
+revertA1 L1.A = L.A 0
+revertA1 L1.B = L.B
+
+revertA2 :: L2.A -> L.A
+revertA2 (L2.A x) = L.A x
+revertA2 L2.B = L.B
+
+
+hooks_show :: L.A -> HooksM String
+hooks_show a = do
+  ver <- asks hooksVersion
+  case ver of
+    V01 -> readHooksExe "show" (convertA1 a)
+    V02 -> readHooksExe "show" (convertA2 a)
+
+hooks_inc :: L.A -> HooksM L.A
+hooks_inc a = do
+  ver <- asks hooksVersion
+  case ver of
+    V01 -> revertA1 <$> (readHooksExe "inc" (convertA1 a))
+    V02 -> revertA2 <$> (readHooksExe "inc" (convertA2 a))
+
+
+
+
+-- Library funcs
+
+
+readHooksExe :: (Binary a, Binary b) => String -> a -> HooksM b
+readHooksExe hook args = do
+  exe <- asks hooksExe
+  liftIO $ readHooksExe_ exe hook args
+
+withForkWait :: IO () -> (IO () ->  IO a) -> IO a
+withForkWait async body = do
+  waitVar <- newEmptyMVar :: IO (MVar (Either SomeException ()))
+  mask $ \restore -> do
+    tid <- forkIO $ try (restore async) >>= putMVar waitVar
+    let wait = takeMVar waitVar >>= either throwIO return
+    restore (body wait) `C.onException` killThread tid
+
+readHooksExe_ :: (Binary a, Binary b) => FilePath -> String -> a -> IO b
+readHooksExe_ exe hook args =
+  let stdin_ = encode args
+      cp = (proc exe [hook]) { std_in = CreatePipe
+                             , std_out = CreatePipe }
+  in withCreateProcess cp $ \(Just inh) (Just outh) Nothing ph -> do
+      -- fork off a thread to start consuming the output
+        hSetBuffering inh NoBuffering
+        hSetBuffering outh NoBuffering
+        output  <- hGetContents outh
+        withForkWait (C.evaluate $ rnf output) $ \waitOut -> do
+
+          hPutStr inh stdin_
+          -- hClose performs implicit hFlush, and thus may trigger a SIGPIPE
+          ignoreSigPipe $ hClose inh
+
+          -- wait on the output
+          waitOut
+          hClose outh
+
+        -- wait on the process
+        _ex <- waitForProcess ph
+        return (decode output)
+
+
+
+-- | Ignore SIGPIPE in a subcomputation.
+ignoreSigPipe :: IO () -> IO ()
+ignoreSigPipe = C.handle $ \case
+  GHC.IOError{GHC.ioe_type = GHC.ResourceVanished, GHC.ioe_errno = Just ioe}
+    | Errno ioe == ePIPE -> return ()
+  e -> throwIO e
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/MyLib.hs
new file mode 100644
index 00000000000..e657c4403f6
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/hooks-lib/src/MyLib.hs
@@ -0,0 +1,4 @@
+module MyLib (someFunc) where
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/CHANGELOG.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/CHANGELOG.md
new file mode 100644
index 00000000000..6b7696f9f1e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for main-prog
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/app/Main.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/app/Main.hs
new file mode 100644
index 00000000000..8cd9037f565
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/app/Main.hs
@@ -0,0 +1,21 @@
+-- This is linked directly against lib, but can communicate with older versions of
+-- lib via the hooks executable.
+module Main where
+
+import System.Directory
+import Lib
+import HooksLib
+import Control.Monad.IO.Class
+import System.Environment
+
+main :: IO ()
+main = do
+  -- Receive the path to the hooks_exe as an argument
+  [hooks_exe] <- getArgs
+  withHooksExe hooks_exe $ do
+    liftIO $ putStr "hooks_show: "
+    rendered <- hooks_show (A 5)
+    liftIO $ putStrLn rendered
+    liftIO $ putStr "hooks_inc: "
+    a' <- hooks_inc (A 5)
+    liftIO $ print a'
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/main-prog.cabal b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/main-prog.cabal
new file mode 100644
index 00000000000..56f5ddfa5e5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/main-prog/main-prog.cabal
@@ -0,0 +1,18 @@
+cabal-version:   3.0
+name:            main-prog
+version:         0.1.0.0
+license:         NONE
+author:          matthewtpickering@gmail.com
+maintainer:      Matthew Pickering
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+executable main-prog
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    base, lib01, directory, hooks-lib
+    hs-source-dirs:   app
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/CHANGELOG.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/CHANGELOG.md
new file mode 100644
index 00000000000..6a8c7fe311e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for lib01
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/lib01.cabal b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/lib01.cabal
new file mode 100644
index 00000000000..1fc1ad750b9
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/lib01.cabal
@@ -0,0 +1,18 @@
+cabal-version:   3.0
+name:            lib01
+version:         0.1.0.0
+license:         NONE
+author:          matthewtpickering@gmail.com
+maintainer:      Matthew Pickering
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  Lib
+    build-depends:    base, binary
+    hs-source-dirs:   src
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/src/Lib.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/src/Lib.hs
new file mode 100644
index 00000000000..5c3bf43eabc
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.1.0.0/src/Lib.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE DeriveAnyClass #-}
+module Lib(A(..), inc) where
+
+import Data.Binary
+import GHC.Generics
+
+data A = A | B deriving (Show, Generic)
+
+deriving instance Binary A
+
+inc :: A -> A
+inc A = B
+inc B = B
+
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/CHANGELOG.md b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/CHANGELOG.md
new file mode 100644
index 00000000000..6a8c7fe311e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for lib01
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/lib01.cabal b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/lib01.cabal
new file mode 100644
index 00000000000..da908f3f043
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/lib01.cabal
@@ -0,0 +1,18 @@
+cabal-version:   3.0
+name:            lib01
+version:         0.2.0.0
+license:         NONE
+author:          matthewtpickering@gmail.com
+maintainer:      Matthew Pickering
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  Lib
+    build-depends:    base, binary
+    hs-source-dirs:   src
+    default-language: Haskell2010
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/src/Lib.hs b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/src/Lib.hs
new file mode 100644
index 00000000000..24ce215cd70
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/cabal-hooks-demo/repo/lib01-0.2.0.0/src/Lib.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE DeriveAnyClass #-}
+module Lib(A(..), inc) where
+
+import Data.Binary
+import GHC.Generics
+
+data A = A { value :: Int } | B deriving (Show, Generic)
+
+deriving instance Binary A
+
+inc :: A -> A
+inc (A {}) = B
+inc B = B
+
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/README.md b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/README.md
new file mode 100644
index 00000000000..573957a03fa
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/README.md
@@ -0,0 +1,30 @@
+Closure property test
+
+package a-0.1
+ :private-build-depends: G0 with (b, d)
+
+package a-0.2
+ :build-depends: c
+ :private-build-depends: G0 with (b, d)
+
+package b-0.1
+ :build-depends: x
+
+package b-0.2
+ :build-depends: x, d
+
+package b-0.3
+ :build-depends: x, c, d
+
+package c-0.1
+ :build-depends: x
+
+package c-0.2
+ :build-depends: x, d
+
+
+Closure property violated by `b == 0.3` and `c == 0.2` THEN closure property is violated.
+
+Need to be able to implicitly introduce c into the private scope so that the closure property holds.
+Or otherwise pick an older version of C which does not depend on D
+
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.1 b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.1
new file mode 100644
index 00000000000..1d6fdeb5c43
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.1
@@ -0,0 +1 @@
+packages: libA-0.1.0.0
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.2 b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.2
new file mode 100644
index 00000000000..6a6ab0dcb42
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.2
@@ -0,0 +1 @@
+packages: libA-0.2.0.0
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.3 b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.3
new file mode 100644
index 00000000000..50ad944ca45
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.3
@@ -0,0 +1 @@
+packages: libA-0.3.0.0
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.4 b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.4
new file mode 100644
index 00000000000..a62ce97ac49
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.project.4
@@ -0,0 +1 @@
+packages: libA-0.4.0.0
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.test.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.test.hs
new file mode 100644
index 00000000000..13215233402
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/cabal.test.hs
@@ -0,0 +1,29 @@
+import Test.Cabal.Prelude
+
+main = do
+  cabalTest $ recordMode DoNotRecord $ do
+
+    -- Will violate closure property
+    withProjectFile "cabal.project.1" $
+      withRepo "repo" $
+        fails (cabal' "v2-build" ["libA"])
+          >>= assertOutputContains "private scopes must contain its closure, but package libC is not included in the private scope libA:lib:G0"
+
+    -- Must pick libC == 0.1
+    withProjectFile "cabal.project.2" $
+      withRepo "repo" $
+        cabal' "v2-build" ["libA"]
+          >>= assertOutputContains "libC-0.1.0.0"
+
+    -- Shouldn't pick libB == 0.3 because it violates closure property
+    withProjectFile "cabal.project.3" $
+      withRepo "repo" $
+        cabal' "v2-build" ["libA"]
+          >>= assertOutputDoesNotContain "libB-0.3.0.0"
+
+    -- Will be OKay with libB == 0.3 and libC == 0.2 because libC is in the closure
+    withProjectFile "cabal.project.4" $
+      withRepo "repo" $ do
+        o <- cabal' "v2-build" ["libA"]
+        assertOutputContains "libC-0.2.0.0" o
+        assertOutputContains "libB-0.3.0.0" o
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/MyLib.hs
new file mode 100644
index 00000000000..dc2cb96275e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = ""
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/libA.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/libA.cabal
new file mode 100644
index 00000000000..f92995fdacf
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.1.0.0/libA.cabal
@@ -0,0 +1,13 @@
+cabal-version:      3.0
+name:               libA
+version:            0.1.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    -- Will violate closure property
+    private-build-depends: G0 with (libB == 0.1.0.0,libD)
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/libA.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/libA.cabal
new file mode 100644
index 00000000000..56bdf19a058
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.2.0.0/libA.cabal
@@ -0,0 +1,14 @@
+cabal-version:      3.0
+name:               libA
+version:            0.2.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libC
+    -- Must pick libC == 0.1
+    private-build-depends: G0 with (libB == 0.2.0.0,libD)
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/libA.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/libA.cabal
new file mode 100644
index 00000000000..90f84cd5a36
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.3.0.0/libA.cabal
@@ -0,0 +1,14 @@
+cabal-version:      3.0
+name:               libA
+version:            0.3.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libC
+    -- Shouldn't pick libB == 0.3 because it violates closure property
+    private-build-depends: G0 with (libB,libD)
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/libA.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/libA.cabal
new file mode 100644
index 00000000000..ec556d108ac
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/libA-0.4.0.0/libA.cabal
@@ -0,0 +1,13 @@
+cabal-version:      3.0
+name:               libA
+version:            0.4.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    -- Will be OKay with libB == 0.3 and libC == 0.2 because libC is in the closure
+    private-build-depends: G0 with (libB == 0.3.0.0, libC, libD)
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/libB.cabal
new file mode 100644
index 00000000000..0b368f60db2
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.1.0.0/libB.cabal
@@ -0,0 +1,12 @@
+cabal-version:      3.0
+name:               libB
+version:            0.1.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libC == 0.2.0.0
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/libB.cabal
new file mode 100644
index 00000000000..010de751424
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.2.0.0/libB.cabal
@@ -0,0 +1,12 @@
+cabal-version:      3.0
+name:               libB
+version:            0.2.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libC
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/libB.cabal
new file mode 100644
index 00000000000..cb0ff52869e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libB-0.3.0.0/libB.cabal
@@ -0,0 +1,12 @@
+cabal-version:      3.0
+name:               libB
+version:            0.3.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libC == 0.2.0.0, libD
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/libC.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/libC.cabal
new file mode 100644
index 00000000000..abb9ae3482a
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.1.0.0/libC.cabal
@@ -0,0 +1,11 @@
+cabal-version:      3.0
+name:               libC
+version:            0.1.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/libC.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/libC.cabal
new file mode 100644
index 00000000000..3dd472acc3a
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libC-0.2.0.0/libC.cabal
@@ -0,0 +1,12 @@
+cabal-version:      3.0
+name:               libC
+version:            0.2.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    build-depends:    libD
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/MyLib.hs b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/MyLib.hs
new file mode 100644
index 00000000000..6c63822a95f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/MyLib.hs
@@ -0,0 +1,3 @@
+module MyLib (someFunc) where
+
+someFunc = "someFunc"
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/libD.cabal b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/libD.cabal
new file mode 100644
index 00000000000..117350487c7
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/closure-property-test/repo/libD-0.1.0.0/libD.cabal
@@ -0,0 +1,11 @@
+cabal-version:      3.0
+name:               libD
+version:            0.1.0.0
+license:            NONE
+build-type:         Simple
+
+library
+    exposed-modules:  MyLib
+    hs-source-dirs:   .
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/README.md b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/README.md
new file mode 100644
index 00000000000..57d9e02f886
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/README.md
@@ -0,0 +1,15 @@
+Backpack + Private Dependencies test
+
+exeA
+    main-is: Main.hs
+    private-build-depends: G1 with (libB == 0.1.0.0)
+    private-build-depends: G2 with (libB == 0.2.0.0)
+    build-depends: libB == 0.3.0.0
+    mixins:
+        libA (A as A.G1) requires (AHole as G1.Fill)
+        libA (A as A.G2) requires (AHole as G2.Fill)
+        libA (A as A.NoScope) requires (AHole as Fill)
+
+libA
+    exposed-modules: A
+    signatures: AHole
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.project b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.project
new file mode 100644
index 00000000000..827fcfc78cf
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.project
@@ -0,0 +1 @@
+packages: libA
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.test.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.test.hs
new file mode 100644
index 00000000000..c740c372052
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/cabal.test.hs
@@ -0,0 +1,9 @@
+import Test.Cabal.Prelude
+
+main =
+    cabalTest $
+      expectBroken 0 $
+        withProjectFile "cabal.project" $
+          withRepo "repo" $
+            cabal "v2-build" ["libA"]
+
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/app/Main.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/app/Main.hs
new file mode 100644
index 00000000000..6d78a77a66a
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/app/Main.hs
@@ -0,0 +1,8 @@
+import qualified A.G1
+import qualified A.G2
+import qualified A.NoScope
+
+main = do
+  print (A.G1.fillhole)
+  print (A.G2.fillhole)
+  print (A.NoScope.fillhole)
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/libA.cabal b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/libA.cabal
new file mode 100644
index 00000000000..4e9ec21c5cb
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/libA.cabal
@@ -0,0 +1,22 @@
+cabal-version:   3.0
+name:            libA
+version:         0.1.0.0
+license:         NONE
+build-type:      Simple
+
+executable exeA
+    main-is: Main.hs
+    build-depends: libA, libB == 0.3.0.0
+    private-build-depends: G1 with (libB == 0.1.0.0)
+    private-build-depends: G2 with (libB == 0.2.0.0)
+    mixins:
+      libA (A as A.G1) requires (AHole as G1.Fill),
+      libA (A as A.G2) requires (AHole as G2.Fill),
+      libA (A as A.NoScope) requires (AHole as Fill)
+    default-extensions: NoImplicitPrelude
+
+library
+    exposed-modules: A
+    signatures: AHole
+    hs-source-dirs: src
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/A.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/A.hs
new file mode 100644
index 00000000000..d1a60e710e2
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/A.hs
@@ -0,0 +1,3 @@
+module A (fillhole) where
+
+import AHole (fillhole)
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/AHole.hsig b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/AHole.hsig
new file mode 100644
index 00000000000..9ceafbd086e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/libA/src/AHole.hsig
@@ -0,0 +1,3 @@
+signature AHole where
+
+fillhole :: Int
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/Fill.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/Fill.hs
new file mode 100644
index 00000000000..fef98a6ce08
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/Fill.hs
@@ -0,0 +1,4 @@
+module Fill where
+
+fillhole :: Int
+fillhole = 1
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/libB.cabal
new file mode 100644
index 00000000000..e5937452a61
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/libB.cabal
@@ -0,0 +1,10 @@
+cabal-version:   3.0
+name:            libB
+version:         0.1.0.0
+license:         NONE
+build-type:      Simple
+
+library
+    exposed-modules:  Fill
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/tags b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/tags
new file mode 100644
index 00000000000..1a01b2d1ce5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.1.0.0/tags
@@ -0,0 +1,2 @@
+!_TAG_FILE_SORTED	1	//
+fillhole	Fill.hs	3;"	f
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/Fill.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/Fill.hs
new file mode 100644
index 00000000000..fd4cd35d6d6
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/Fill.hs
@@ -0,0 +1,4 @@
+module Fill where
+
+fillhole :: Int
+fillhole = 2
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/libB.cabal
new file mode 100644
index 00000000000..0f8cd48746f
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/libB.cabal
@@ -0,0 +1,10 @@
+cabal-version:   3.0
+name:            libB
+version:         0.2.0.0
+license:         NONE
+build-type:      Simple
+
+library
+    exposed-modules:  Fill
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/tags b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/tags
new file mode 100644
index 00000000000..1a01b2d1ce5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.2.0.0/tags
@@ -0,0 +1,2 @@
+!_TAG_FILE_SORTED	1	//
+fillhole	Fill.hs	3;"	f
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/Fill.hs b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/Fill.hs
new file mode 100644
index 00000000000..234f38660cb
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/Fill.hs
@@ -0,0 +1,4 @@
+module Fill where
+
+fillhole :: Int
+fillhole = 3
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/libB.cabal b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/libB.cabal
new file mode 100644
index 00000000000..5f7b5cc4f98
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/libB.cabal
@@ -0,0 +1,10 @@
+cabal-version:   3.0
+name:            libB
+version:         0.3.0.0
+license:         NONE
+build-type:      Simple
+
+library
+    exposed-modules:  Fill
+    default-language: Haskell2010
+    default-extensions: NoImplicitPrelude
diff --git a/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/tags b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/tags
new file mode 100644
index 00000000000..1a01b2d1ce5
--- /dev/null
+++ b/cabal-testsuite/PackageTests/PrivateDeps/pd-backpack/repo/libB-0.3.0.0/tags
@@ -0,0 +1,2 @@
+!_TAG_FILE_SORTED	1	//
+fillhole	Fill.hs	3;"	f
diff --git a/cabal-testsuite/src/Test/Cabal/Prelude.hs b/cabal-testsuite/src/Test/Cabal/Prelude.hs
index 69e60078e78..f2743dcbaf7 100644
--- a/cabal-testsuite/src/Test/Cabal/Prelude.hs
+++ b/cabal-testsuite/src/Test/Cabal/Prelude.hs
@@ -374,7 +374,9 @@ runPlanExe' pkg_name cname args = do
     recordHeader [pkg_name, cname]
     runM exePath args Nothing
 
-planExePath :: String {- package name -} -> String {- component name -}
+-- | Get the path to an executable built from a package. Requires 'withPlan'
+-- to have been run so that we can find the dist dir.
+planExePath :: String {-^ package name -} -> String {-^ component name -}
             -> TestM FilePath
 planExePath pkg_name cname = do
     Just plan <- testPlan `fmap` getTestEnv
diff --git a/doc/buildinfo-fields-reference.rst b/doc/buildinfo-fields-reference.rst
index dd8c505a85e..5aaae92cab1 100644
--- a/doc/buildinfo-fields-reference.rst
+++ b/doc/buildinfo-fields-reference.rst
@@ -510,6 +510,13 @@ pkgconfig-depends
     .. math::
         \mathrm{commalist}\mathsf{\color{red}{TODO}}
 
+private-build-depends
+    * Monoidal field
+    * Documentation of :pkg-field:`library:private-build-depends`
+
+    .. math::
+        \mathrm{commalist}\left(\mathop{\mathit{alias}}\bullet\mathop{\mathord{``}\mathtt{with}\mathord{"}}\bullet\mathop{\mathord{``}\mathtt{\text{(}}\mathord{"}}\circ{\left(\mathop{\mathit{pkg\text{-}name}}{\left(\mathop{\mathord{``}\mathtt{\text{:}}\mathord{"}}\left\{ \mathop{\mathit{unqual\text{-}name}}\mid\mathop{\mathord{``}\mathtt{\{}\mathord{"}}\circ{\mathop{\mathit{unqual\text{-}name}}}^+_{\left(\circ\mathop{\mathord{``}\mathtt{\text{,}}\mathord{"}}\circ\right)}\circ\mathop{\mathord{``}\mathtt{\}}\mathord{"}} \right\}\right)}^?{\left(\circ\mathop{\mathit{version\text{-}range}}\right)}^?\right)}^\ast_{\left(\circ\mathop{\mathord{``}\mathtt{\text{,}}\mathord{"}}\circ\right)}\circ\mathop{\mathord{``}\mathtt{\text{)}}\mathord{"}}\right)
+
 virtual-modules
     * Monoidal field
     * Available since ``cabal-version: 2.2``.
diff --git a/doc/cabal-package-description-file.rst b/doc/cabal-package-description-file.rst
index 652746b216a..53ffdd600eb 100644
--- a/doc/cabal-package-description-file.rst
+++ b/doc/cabal-package-description-file.rst
@@ -2133,6 +2133,10 @@ system-dependent values for these fields.
     supported libraries. Depending on your system you may need to adjust
     ``PKG_CONFIG_PATH``.
 
+.. pkg-field:: private-build-depends: private scope
+
+    `private-build-depends` introduces a new private scope,... TODO
+
 .. pkg-field:: frameworks: token list
 
     On Darwin/MacOS X, a list of frameworks to link to. See Apple's