Modify the GHC_ENVIRONMENT env var in Stack.Setup

ChangeLog.md

@@ -160,7 +160,7 @@ Other enhancements:
 * Include default values for most command line flags in the `--help`
   output. See
   [#893](https://github.com/commercialhaskell/stack/issues/893).
-* environment variable `GHC_ENVIRONMENT` is set to specify dependency
+* Set the `GHC_ENVIRONMENT` environment variable to specify dependency
   packages explicitly when running test. This is done to prevent
   ambiguous module name errors in `doctest` tests.
 - Document the way stack interacts with the Cabal library.
@@ -181,6 +181,13 @@ Other enhancements:
 * User config files are respected for the script command. See
   [#3705](https://github.com/commercialhaskell/stack/issues/3705),
   [#3887](https://github.com/commercialhaskell/stack/issues/3887).
+* Set the `GHC_ENVIRONMENT` environment variable to `-` to tell GHC to
+  ignore any such files when GHC is new enough (>= 8.4.4), otherwise
+  simply unset the variable. This allows Stack to have control of
+  package databases when running commands like `stack exec ghci`, even
+  in the presence of implicit environment files created by `cabal
+  new-build`. See
+  [#4706](https://github.com/commercialhaskell/stack/issues/4706).
 
 Bug fixes:
 

src/Stack/Setup.hs

@@ -345,7 +345,18 @@ setupEnv needTargets boptsCLI mResolveMissingGHC = do
                                         [ toFilePathNoTrailingSep deps
                                         , ""
                                         ])
-                        $ Map.insert "HASKELL_DIST_DIR" (T.pack $ toFilePathNoTrailingSep distDir) env
+                        $ Map.insert "HASKELL_DIST_DIR" (T.pack $ toFilePathNoTrailingSep distDir)
+
+                          -- Make sure that any .ghc.environment files
+                          -- are ignored, since we're settting up our
+                          -- own package databases. See
+                          -- https://github.com/commercialhaskell/stack/issues/4706
+                        $ (case cpCompilerVersion compilerPaths of
+                             ACGhc version | version >= mkVersion [8, 4, 4] ->
+                               Map.insert "GHC_ENVIRONMENT" "-"
+                             _ -> id)
+
+                          env
 
                     () <- atomicModifyIORef envRef $ \m' ->
                         (Map.insert es eo m', ())
@@ -1773,6 +1784,7 @@ removeHaskellEnvVars :: Map Text Text -> Map Text Text
 removeHaskellEnvVars =
     Map.delete "GHCJS_PACKAGE_PATH" .
     Map.delete "GHC_PACKAGE_PATH" .
+    Map.delete "GHC_ENVIRONMENT" .
     Map.delete "HASKELL_PACKAGE_SANDBOX" .
     Map.delete "HASKELL_PACKAGE_SANDBOXES" .
     Map.delete "HASKELL_DIST_DIR" .

test/integration/tests/4706-ignore-ghc-env-files/Main.hs

@@ -0,0 +1,27 @@
+import StackTest
+import Control.Exception (bracket_)
+import Control.Monad (when)
+import System.Environment
+import System.Directory
+import System.Info (arch, os)
+
+main :: IO ()
+main = when False $ do -- skip this test until we start using GHC 8.4.4 or later for integration tests
+  let ghcVer = "8.4.4"
+      fp = concat
+        [ ".ghc.environment."
+        , arch
+        , "-"
+        , os
+        , "-"
+        , ghcVer
+        ]
+  writeFile "stack.yaml" $ "resolver: ghc-" ++ ghcVer
+  bracket_
+    (writeFile fp "This is an invalid GHC environment file")
+    (removeFile fp) $ do
+      envFile <- canonicalizePath fp
+      setEnv "GHC_ENVIRONMENT" envFile
+      stack ["clean"]
+      stack ["build"]
+      stack ["runghc", "Main.hs"]

test/integration/tests/4706-ignore-ghc-env-files/files/.gitignore

@@ -0,0 +1,2 @@
+foo.cabal
+stack.yaml

test/integration/tests/4706-ignore-ghc-env-files/files/Main.hs

@@ -0,0 +1,2 @@
+main :: IO ()
+main = pure ()

test/integration/tests/4706-ignore-ghc-env-files/files/package.yaml

@@ -0,0 +1,7 @@
+name: foo
+version: 0
+
+dependencies:
+- base
+
+library: {}