Fix nix config option (haskell#8522)

* Fix nix config option

* Add changelog file

* Fix whitespace

* Reduce string to bool flag fn

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

cabal-install/src/Distribution/Client/Setup.hs

@@ -364,6 +364,11 @@ globalCommand commands = CommandUI {
       ,multiOption "nix"
         globalNix (\v flags -> flags { globalNix = v })
         [
+          optArg' "(True or False)" (maybeToFlag . (readMaybe =<<)) (\case
+            Flag True -> [Just "enable"]
+            Flag False -> [Just "disable"]
+            NoFlag -> [Just "disable"]) "" ["nix"]
+            "Nix integration: run commands through nix-shell if a 'shell.nix' file exists (default is False)",
           noArg (Flag True) [] ["enable-nix"]
           "Enable Nix integration: run commands through nix-shell if a 'shell.nix' file exists",
           noArg (Flag False) [] ["disable-nix"]
@@ -413,7 +418,6 @@ globalCommand commands = CommandUI {
          "Set a location for a cabal.config file for projects without their own cabal.config freeze file."
          globalConstraintsFile (\v flags -> flags {globalConstraintsFile = v})
          (reqArgFlag "FILE")
-
       ]
 
 -- ------------------------------------------------------------

cabal-install/tests/IntegrationTests2.hs

@@ -50,6 +50,7 @@ import Distribution.PackageDescription
 import Distribution.InstalledPackageInfo (InstalledPackageInfo)
 import Distribution.Simple.Setup (toFlag, HaddockFlags(..), defaultHaddockFlags)
 import Distribution.Client.Setup (globalCommand)
+import Distribution.Client.Config (loadConfig, SavedConfig(savedGlobalFlags))
 import Distribution.Simple.Compiler
 import Distribution.Simple.Command
 import qualified Distribution.Simple.Flag as Flag
@@ -1954,6 +1955,15 @@ testNixFlags = do
   Just True @=? (fromFlag . globalNix . fromJust $ nixEnabledFlags)
   Just False @=? (fromFlag . globalNix . fromJust $ nixDisabledFlags)
   Nothing @=? (fromFlag . globalNix . fromJust $ nixDefaultFlags)
+
+  -- Config file options
+  defaultConfig <- loadConfig verbosity (Flag (basedir </> "nix-config/default-config"))
+  trueConfig <- loadConfig verbosity (Flag (basedir </> "nix-config/nix-true"))
+  falseConfig <- loadConfig verbosity (Flag (basedir </> "nix-config/nix-false"))
+
+  Nothing @=? (fromFlag . globalNix . savedGlobalFlags $ defaultConfig)
+  Just True @=? (fromFlag . globalNix . savedGlobalFlags $ trueConfig)
+  Just False @=? (fromFlag . globalNix . savedGlobalFlags $ falseConfig)
   where
     fromFlag :: Flag Bool -> Maybe Bool
     fromFlag (Flag x) = Just x

cabal-install/tests/IntegrationTests2/nix-config/default-config

@@ -0,0 +1,229 @@
+-- This is the configuration file for the 'cabal' command line tool.
+--
+-- The available configuration options are listed below.
+-- Some of them have default values listed.
+--
+-- Lines (like this one) beginning with '--' are comments.
+-- Be careful with spaces and indentation because they are
+-- used to indicate layout for nested sections.
+--
+-- This config file was generated using the following versions
+-- of Cabal and cabal-install:
+-- Cabal library version: 3.6.2.0
+-- cabal-install version: 3.6.2.0
+
+
+repository hackage.haskell.org
+  url: http://hackage.haskell.org/
+  -- secure: True
+  -- root-keys:
+  -- key-threshold: 3
+
+-- default-user-config:
+-- ignore-expiry: False
+-- http-transport:
+-- nix: False
+-- local-no-index-repo:
+
+--debug-info: 1
+-- store-dir:
+-- active-repositories:
+-- verbose: 1
+-- compiler: ghc
+-- cabal-file:
+-- with-compiler:
+-- with-hc-pkg:
+-- program-prefix: 
+-- program-suffix: 
+-- library-vanilla: True
+-- library-profiling:
+-- shared:
+-- static:
+-- executable-dynamic: False
+-- executable-static: False
+-- profiling:
+-- executable-profiling:
+-- profiling-detail:
+-- library-profiling-detail:
+-- optimization: True
+-- debug-info: False
+-- library-for-ghci:
+-- split-sections: False
+-- split-objs: False
+-- executable-stripping:
+-- library-stripping:
+-- configure-option:
+-- user-install: True
+-- package-db:
+-- flags:
+-- extra-include-dirs:
+-- deterministic:
+-- cid:
+-- extra-lib-dirs:
+-- extra-framework-dirs:
+-- instantiate-with:
+-- tests: False
+-- coverage: False
+-- library-coverage:
+-- exact-configuration: False
+-- benchmarks: False
+-- relocatable: False
+-- response-files:
+-- allow-depending-on-private-libs:
+-- cabal-lib-version:
+-- constraint:
+-- preference:
+-- solver: modular
+-- allow-older: False
+-- allow-newer: False
+-- write-ghc-environment-files:
+-- documentation: False
+-- doc-index-file: $datadir/doc/$arch-$os-$compiler/index.html
+-- only-download: False
+-- target-package-db:
+-- max-backjumps: 4000
+-- reorder-goals: False
+-- count-conflicts: True
+-- fine-grained-conflicts: True
+-- minimize-conflict-set: False
+-- independent-goals: False
+-- shadow-installed-packages: False
+-- strong-flags: False
+-- allow-boot-library-installs: False
+-- reject-unconstrained-dependencies: none
+-- reinstall: False
+-- avoid-reinstalls: False
+-- force-reinstalls: False
+-- upgrade-dependencies: False
+-- index-state:
+-- root-cmd:
+-- symlink-bindir:
+-- build-log:
+remote-build-reporting: none
+-- report-planning-failure: False
+-- per-component: True
+-- one-shot: False
+-- run-tests:
+jobs: $ncpus
+-- keep-going: False
+-- offline: False
+-- lib: False
+-- package-env:
+-- overwrite-policy:
+-- install-method:
+-- username:
+-- password:
+-- password-command:
+-- builddir:
+
+haddock
+  -- keep-temp-files: False
+  -- hoogle: False
+  -- html: False
+  -- html-location:
+  -- executables: False
+  -- tests: False
+  -- benchmarks: False
+  -- foreign-libraries: False
+  -- all:
+  -- internal: False
+  -- css:
+  -- hyperlink-source: False
+  -- quickjump: False
+  -- hscolour-css:
+  -- contents-location:
+
+init
+  -- interactive: False
+  -- cabal-version: 2.4
+  -- license:
+  -- tests:
+  -- test-dir:
+  -- language: Haskell2010
+  -- application-dir: app
+  -- source-dir: src
+
+install-dirs user
+  -- bindir: $prefix/bin
+  -- libdir: $prefix/lib
+  -- libsubdir: $abi/$libname
+  -- dynlibdir: $libdir/$abi
+  -- libexecdir: $prefix/libexec
+  -- libexecsubdir: $abi/$pkgid
+  -- datadir: $prefix/share
+  -- datasubdir: $abi/$pkgid
+  -- docdir: $datadir/doc/$abi/$pkgid
+  -- htmldir: $docdir/html
+  -- haddockdir: $htmldir
+  -- sysconfdir: $prefix/etc
+
+install-dirs global
+  -- prefix: /usr/local
+  -- bindir: $prefix/bin
+  -- libdir: $prefix/lib
+  -- libsubdir: $abi/$libname
+  -- dynlibdir: $libdir/$abi
+  -- libexecdir: $prefix/libexec
+  -- libexecsubdir: $abi/$pkgid
+  -- datadir: $prefix/share
+  -- datasubdir: $abi/$pkgid
+  -- docdir: $datadir/doc/$abi/$pkgid
+  -- htmldir: $docdir/html
+  -- haddockdir: $htmldir
+  -- sysconfdir: $prefix/etc
+
+program-locations
+  -- alex-location:
+  -- ar-location:
+  -- c2hs-location:
+  -- cpphs-location:
+  -- doctest-location:
+  -- gcc-location:
+  -- ghc-location:
+  -- ghc-pkg-location:
+  -- ghcjs-location:
+  -- ghcjs-pkg-location:
+  -- greencard-location:
+  -- haddock-location:
+  -- happy-location:
+  -- haskell-suite-location:
+  -- haskell-suite-pkg-location:
+  -- hmake-location:
+  -- hpc-location:
+  -- hsc2hs-location:
+  -- hscolour-location:
+  -- jhc-location:
+  -- ld-location:
+  -- pkg-config-location:
+  -- runghc-location:
+  -- strip-location:
+  -- tar-location:
+  -- uhc-location:
+
+program-default-options
+  -- alex-options:
+  -- ar-options:
+  -- c2hs-options:
+  -- cpphs-options:
+  -- doctest-options:
+  -- gcc-options:
+  -- ghc-options:
+  -- ghc-pkg-options:
+  -- ghcjs-options:
+  -- ghcjs-pkg-options:
+  -- greencard-options:
+  -- haddock-options:
+  -- happy-options:
+  -- haskell-suite-options:
+  -- haskell-suite-pkg-options:
+  -- hmake-options:
+  -- hpc-options:
+  -- hsc2hs-options:
+  -- hscolour-options:
+  -- jhc-options:
+  -- ld-options:
+  -- pkg-config-options:
+  -- runghc-options:
+  -- strip-options:
+  -- tar-options:
+  -- uhc-options: