For ghc calls pass Cabal's build/ directory after user's src/ directory so that contents of src/ takes precedence (#8690)

* Add test

* Pass build/ directory after src/ so that whatever’s in src/ will override any files we autogenerated

* Add expected output. Constrait test to run on recent enough ghc that will have Cabal updated

* Force test to requre development version of Cabal

Otherwise output will not be correct. It’s tricky to pass proper
Cabal/ version to this test because it needs it for the custom setup.

* Add changelog

* Fix other tests

Author: sergv

Cabal/src/Distribution/Simple/GHC/Internal.hs

@@ -442,7 +442,8 @@ componentGhcOptions verbosity implInfo lbi bi clbi odir =
       ghcOptSplitSections   = toFlag (splitSections lbi),
       ghcOptSplitObjs       = toFlag (splitObjs lbi),
       ghcOptSourcePathClear = toFlag True,
-      ghcOptSourcePath      = toNubListR $ [odir] ++ (map getSymbolicPath (hsSourceDirs bi))
+      ghcOptSourcePath      = toNubListR $ map getSymbolicPath (hsSourceDirs bi)
+                                           ++ [odir]
                                            ++ [autogenComponentModulesDir lbi clbi]
                                            ++ [autogenPackageModulesDir lbi],
       ghcOptCppIncludePath  = toNubListR $ [autogenComponentModulesDir lbi clbi

cabal-testsuite/PackageTests/AutogenModulesToggling/Main.hs

@@ -0,0 +1,12 @@
+module Main (main) where
+
+import Lib (bar)
+
+main :: IO ()
+main = do
+  -- Make sure cabal sees this because this test is about which
+  -- 'Generated' module the 'Lib' was compiled against.
+  putStrLn "-----BEGIN CABAL OUTPUT-----"
+  putStrLn bar
+  putStrLn "-----END CABAL OUTPUT-----"
+

cabal-testsuite/PackageTests/AutogenModulesToggling/Setup.hs

@@ -0,0 +1,24 @@
+
+module Main (main) where
+
+import Distribution.Simple
+import Distribution.Simple.LocalBuildInfo
+import Distribution.Simple.PreProcess
+import Distribution.Simple.Program
+import Distribution.Types.BuildInfo
+import Distribution.Verbosity
+
+import System.Directory
+
+ppHGen :: BuildInfo -> LocalBuildInfo -> ComponentLocalBuildInfo -> PreProcessor
+ppHGen _bi lbi _clbi = PreProcessor
+  { platformIndependent = True
+  , ppOrdering          = unsorted
+  , runPreProcessor     = mkSimplePreProcessor $ \inFile outFile verbosity ->
+      copyFile inFile outFile
+  }
+
+main :: IO ()
+main = defaultMainWithHooks simpleUserHooks
+  { hookedPreProcessors = ("hgen", ppHGen) : hookedPreProcessors simpleUserHooks
+  }

cabal-testsuite/PackageTests/AutogenModulesToggling/cabal.out

@@ -0,0 +1,22 @@
+# cabal v2-run
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - test-0.1 (exe:autogen-toggle-test) (first run)
+Configuring test-0.1...
+Preprocessing library for test-0.1..
+Building library for test-0.1..
+Preprocessing executable 'autogen-toggle-test' for test-0.1..
+Building executable 'autogen-toggle-test' for test-0.1..
+The module says: Real module, ship to production
+# cabal v2-run
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - test-0.1 (exe:autogen-toggle-test) (configuration changed)
+Configuring test-0.1...
+Preprocessing library for test-0.1..
+Building library for test-0.1..
+Preprocessing executable 'autogen-toggle-test' for test-0.1..
+Building executable 'autogen-toggle-test' for test-0.1..
+The module says: Prebuilt module, don't use in production

cabal-testsuite/PackageTests/AutogenModulesToggling/cabal.project

@@ -0,0 +1 @@
+packages: test.cabal

cabal-testsuite/PackageTests/AutogenModulesToggling/cabal.test.hs

@@ -0,0 +1,7 @@
+import Test.Cabal.Prelude
+
+main :: IO ()
+main = cabalTest . recordMode RecordMarked $ do
+  skipUnlessGhcVersion ">= 9.7"
+  cabal "v2-run" ["-fgenerate", "autogen-toggle-test"]
+  cabal "v2-run" ["-f-generate", "autogen-toggle-test"]

cabal-testsuite/PackageTests/AutogenModulesToggling/gen/Generated.hs

@@ -0,0 +1,4 @@
+module Generated (foo) where
+
+foo :: String
+foo = "Prebuilt module, don't use in production"

cabal-testsuite/PackageTests/AutogenModulesToggling/src-inputs/Generated.hgen

@@ -0,0 +1,4 @@
+module Generated (foo) where
+
+foo :: String
+foo = "Real module, ship to production"

cabal-testsuite/PackageTests/AutogenModulesToggling/src/Lib.hs

@@ -0,0 +1,6 @@
+module Lib (bar) where
+
+import Generated (foo)
+
+bar :: String
+bar = "The module says: " ++ foo

cabal-testsuite/PackageTests/AutogenModulesToggling/test.cabal

@@ -0,0 +1,57 @@
+cabal-version: 3.0
+
+name: test
+version: 0.1
+category: Test
+maintainer: S
+synopsis: Test input
+description: Test input
+license: BSD-3-Clause
+
+extra-source-files:
+  src-inputs/**/*.hgen
+
+build-type: Custom
+
+custom-setup
+  setup-depends: Cabal >= 3.9, base, directory
+
+flag generate
+  description:
+    Generate files instead of using pregenerated ones
+  default:
+    False
+  manual:
+    True
+
+library
+  exposed-modules:
+    Lib
+    Generated
+
+  hs-source-dirs:
+    src
+
+  if flag(generate)
+    hs-source-dirs:
+      src-inputs
+    autogen-modules:
+      Generated
+    -- We don’t use any tools in this case but they’ll have to
+    -- go here
+    -- build-tool-depends:
+    --   alex:alex
+  else
+    hs-source-dirs:
+      gen
+
+  build-depends: base > 4
+  default-language: Haskell2010
+
+executable autogen-toggle-test
+  main-is: Main.hs
+  hs-source-dirs: .
+  default-language: Haskell2010
+  build-depends:
+    , base > 4
+    , test