Last part of addressing #415

cabal-install/Distribution/Client/Dependency.hs

@@ -61,6 +61,7 @@ module Distribution.Client.Dependency (
     removeUpperBounds,
     addDefaultSetupDependencies,
     addSetupCabalMinVersionConstraint,
+    addSetupCabalMaxVersionConstraint,
   ) where
 
 import Distribution.Solver.Modular
@@ -555,6 +556,21 @@ addSetupCabalMinVersionConstraint minVersion =
   where
     cabalPkgname = mkPackageName "Cabal"
 
+-- | Variant of 'addSetupCabalMinVersionConstraint' which sets an
+-- upper bound on @setup.Cabal@ labeled with 'ConstraintSetupCabalMaxVersion'.
+--
+addSetupCabalMaxVersionConstraint :: Version
+                                  -> DepResolverParams -> DepResolverParams
+addSetupCabalMaxVersionConstraint maxVersion =
+    addConstraints
+      [ LabeledPackageConstraint
+          (PackageConstraint (ScopeAnySetupQualifier cabalPkgname)
+                             (PackagePropertyVersion $ earlierVersion maxVersion))
+          ConstraintSetupCabalMaxVersion
+      ]
+  where
+    cabalPkgname = mkPackageName "Cabal"
+
 
 upgradeDependencies :: DepResolverParams -> DepResolverParams
 upgradeDependencies = setPreferenceDefault PreferAllLatest

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -80,6 +80,7 @@ import qualified Distribution.Client.SolverInstallPlan as SolverInstallPlan
 import           Distribution.Client.Dependency
 import           Distribution.Client.Dependency.Types
 import qualified Distribution.Client.IndexUtils as IndexUtils
+import           Distribution.Client.Init (incVersion)
 import           Distribution.Client.Targets (userToPackageConstraint)
 import           Distribution.Client.DistDirLayout
 import           Distribution.Client.SetupWrapper
@@ -950,6 +951,7 @@ planPackages verbosity comp platform solver SolverSettings{..}
                                    . packageDescription)
 
       . addSetupCabalMinVersionConstraint setupMinCabalVersionConstraint
+      . addSetupCabalMaxVersionConstraint setupMaxCabalVersionConstraint
 
       . addPreferences
           -- preferences from the config file or command line
@@ -1039,7 +1041,7 @@ planPackages verbosity comp platform solver SolverSettings{..}
     -- respective major Cabal version bundled with the respective GHC
     -- release).
     --
-    -- GHC 8.4   needs  Cabal >= 2.1  (GHC 8.4.1-rc1 has Cabal-2.1)
+    -- GHC 8.4   needs  Cabal >= 2.2
     -- GHC 8.2   needs  Cabal >= 2.0
     -- GHC 8.0   needs  Cabal >= 1.24
     -- GHC 7.10  needs  Cabal >= 1.22
@@ -1050,6 +1052,10 @@ planPackages verbosity comp platform solver SolverSettings{..}
     -- TODO: long-term, this compatibility matrix should be
     --       stored as a field inside 'Distribution.Compiler.Compiler'
     setupMinCabalVersionConstraint
+      | isGHC, compVer >= mkVersion [8,4,1] = mkVersion [2,2]
+        -- GHC 8.4.1-rc1 (GHC 8.4.0.20180224) still shipped with an
+        -- devel snapshot of Cabal-2.1.0.0; the rule below can be
+        -- dropped at some point
       | isGHC, compVer >= mkVersion [8,4]  = mkVersion [2,1]
       | isGHC, compVer >= mkVersion [8,2]  = mkVersion [2,0]
       | isGHC, compVer >= mkVersion [8,0]  = mkVersion [1,24]
@@ -1060,6 +1066,25 @@ planPackages verbosity comp platform solver SolverSettings{..}
         compFlav = compilerFlavor comp
         compVer  = compilerVersion comp
 
+    -- As we can't predict the future, we also place a global upper
+    -- bound on the lib:Cabal version we know how to interact with:
+    --
+    -- The upper bound is computed by incrementing the current major
+    -- version twice in order to allow for the current version, as
+    -- well as the next adjacent major version (one of which will not
+    -- be released, as only "even major" versions of Cabal are
+    -- released to Hackage or bundled with proper GHC releases).
+    --
+    -- For instance, if the current version of cabal-install is an odd
+    -- development version, e.g.  Cabal-2.1.0.0, then we impose an
+    -- upper bound `setup.Cabal < 2.3`; if `cabal-install` is on a
+    -- stable/release even version, e.g. Cabal-2.2.1.0, the upper
+    -- bound is `setup.Cabal < 2.4`. This gives us enough flexibility
+    -- when dealing with development snapshots of Cabal and cabal-install.
+    --
+    setupMaxCabalVersionConstraint =
+      alterVersion (take 2) $ incVersion 1 $ incVersion 1 cabalVersion
+
 ------------------------------------------------------------------------------
 -- * Install plan post-processing
 ------------------------------------------------------------------------------

cabal-install/Distribution/Solver/Types/ConstraintSource.hs

@@ -49,6 +49,10 @@ data ConstraintSource =
   -- | An internal constraint due to compatibility issues with the Setup.hs
   -- command line interface requires a minimum lower bound on Cabal
   | ConstraintSetupCabalMinVersion
+
+  -- | An internal constraint due to compatibility issues with the Setup.hs
+  -- command line interface requires a maximum upper bound on Cabal
+  | ConstraintSetupCabalMaxVersion
   deriving (Eq, Show, Generic)
 
 instance Binary ConstraintSource
@@ -74,3 +78,5 @@ showConstraintSource ConstraintSourceConfigFlagOrTarget =
 showConstraintSource ConstraintSourceUnknown = "unknown source"
 showConstraintSource ConstraintSetupCabalMinVersion =
     "minimum version of Cabal used by Setup.hs"
+showConstraintSource ConstraintSetupCabalMaxVersion =
+    "maximum version of Cabal used by Setup.hs"

cabal-testsuite/PackageTests/Regression/T4154/install-time-with-constraint.out

@@ -4,5 +4,4 @@ Downloading the latest package list from test-local-repo
 Resolving dependencies...
 Build profile: -w ghc-<GHCVER> -O1
 In order, the following would be built:
- - Cabal-99999 (lib) (requires download & build)
  - time-99999 (lib:time) (first run)

cabal-testsuite/PackageTests/Regression/T4154/install-time-with-constraint.test.hs

@@ -9,7 +9,9 @@ main = cabalTest $ withRepo "repo" $ do
 
   -- Temporarily disabled recording here because output is not stable
   recordMode DoNotRecord $ do
-      -- Constraining all uses of 'time' results in a cyclic dependency
-      -- between 'Cabal' and the new 'time'.
-      r <- fails $ cabal' "new-build" ["time", "--constraint=any.time==99999", "--dry-run"]
-      assertOutputContains "cyclic dependencies; conflict set: time:setup.Cabal, time:setup.time" r
+      r <- fails $ cabal' "new-build" ["time", "--constraint=any.time==99999", "--constraint=setup.Cabal installed", "--dry-run"]
+      -- Constraining all uses of 'time' originally resulted in a cyclic dependency
+      -- between 'Cabal' and the new 'time':
+      -- assertOutputContains "cyclic dependencies; conflict set: time:setup.Cabal, time:setup.time" r
+      -- However, this doesn't work anymore, so instead we more directly look for:
+      assertOutputContains "time:setup.time~>time-99999 (conflict: time:setup.Cabal" r

cabal-testsuite/PackageTests/Regression/T4154/time.cabal

@@ -4,7 +4,7 @@ cabal-version:   >=1.8
 build-type:      Custom
 
 custom-setup
-  setup-depends: base, Cabal == 99999
+  setup-depends: base, Cabal
 
 library
   build-depends: base