Cabal: Always pass -package-env=- to supported GHC versions

mpickering · Mikolaj · commit fb8bb05d9a03 · 2025-03-26T15:59:01.000+01:00
Issue haskell#10759 highlighted the issue that we were not isolating the calls to ghc from the existence of environment files. This manifested in a terminal bug where extra arguments form the environment file were causing a link failure which was due to a combination of haskell#10692. However, even before this bug the test executable was relinked to due to the extra flags from the environment file. ``` Building test suite 'aeson-schemas-test' for aeson-schemas-1.4.2.1... Loaded package environment from /home/runner/work/aeson-schemas/aeson-schemas/dist-newstyle/tmp/environment.-69233/.ghc.environment.x86_64-linux-9.6.6 Loaded package environment from /home/runner/work/aeson-schemas/aeson-schemas/dist-newstyle/tmp/environment.-69233/.ghc.environment.x86_64-linux-9.6.6 [23 of 23] Linking /home/runner/work/aeson-schemas/aeson-schemas/dist-newstyle/build/x86_64-linux/ghc-9.6.6/aeson-schemas-1.4.2.1/t/aeson-schemas-test/build/aeson-schemas-test/aeson-schemas-test [Flags changed] ``` The correct solution is that calls to `ghc` made by `Cabal` should never implicitly use an environment file. This is similar to how `GHC_PACKAGE_PATH` is treated. Fixes haskell#10759
diff --git a/Cabal/src/Distribution/Simple/Program/Builtin.hs b/Cabal/src/Distribution/Simple/Program/Builtin.hs
@@ -104,32 +104,44 @@ ghcProgram :: Program
 ghcProgram =
   (simpleProgram "ghc")
     { programFindVersion = findProgramVersion "--numeric-version" id
-    , -- Workaround for https://gitlab.haskell.org/ghc/ghc/-/issues/8825
-      -- (spurious warning on non-english locales)
-      programPostConf = \_verbosity ghcProg ->
-        do
-          let ghcProg' =
-                ghcProg
-                  { programOverrideEnv =
-                      ("LANGUAGE", Just "en")
-                        : programOverrideEnv ghcProg
-                  }
-              -- Only the 7.8 branch seems to be affected. Fixed in 7.8.4.
-              affectedVersionRange =
-                intersectVersionRanges
-                  (laterVersion $ mkVersion [7, 8, 0])
-                  (earlierVersion $ mkVersion [7, 8, 4])
-          return $
-            maybe
-              ghcProg
-              ( \v ->
-                  if withinRange v affectedVersionRange
-                    then ghcProg'
-                    else ghcProg
-              )
-              (programVersion ghcProg)
+    , programPostConf = ghcPostConf
     , programNormaliseArgs = normaliseGhcArgs
     }
+  where
+    ghcPostConf _verbosity ghcProg = do
+      let setLanguageEnv prog =
+            prog
+              { programOverrideEnv =
+                  ("LANGUAGE", Just "en")
+                    : programOverrideEnv ghcProg
+              }
+
+          ignorePackageEnv prog = prog{programDefaultArgs = "-package-env=-" : programDefaultArgs prog}
+
+          -- Only the 7.8 branch seems to be affected. Fixed in 7.8.4.
+          affectedVersionRange =
+            intersectVersionRanges
+              (laterVersion $ mkVersion [7, 8, 0])
+              (earlierVersion $ mkVersion [7, 8, 4])
+
+          canIgnorePackageEnv = orLaterVersion $ mkVersion [8, 4, 4]
+
+          applyWhen cond f prog = if cond then f prog else prog
+
+      return $
+        maybe
+          ghcProg
+          ( \v ->
+              -- By default, ignore GHC_ENVIRONMENT variable of any package environmnet
+              -- files. See #10759
+              applyWhen (withinRange v canIgnorePackageEnv) ignorePackageEnv
+              -- Workaround for https://gitlab.haskell.org/ghc/ghc/-/issues/8825
+              -- (spurious warning on non-english locales)
+              $
+                applyWhen (withinRange v affectedVersionRange) setLanguageEnv $
+                  ghcProg
+          )
+          (programVersion ghcProg)
 
 runghcProgram :: Program
 runghcProgram =
diff --git a/cabal-install/src/Distribution/Client/CmdExec.hs b/cabal-install/src/Distribution/Client/CmdExec.hs
@@ -46,7 +46,7 @@ import Distribution.Client.ProjectOrchestration
 import Distribution.Client.ProjectPlanOutput
   ( PostBuildProjectStatus
   , argsEquivalentOfGhcEnvironmentFile
-  , createPackageEnvironment
+  , createPackageEnvironmentAndArgs
   , updatePostBuildProjectStatus
   )
 import Distribution.Client.ProjectPlanning
@@ -191,7 +191,7 @@ execAction flags@NixStyleFlags{..} extraArgs globalFlags = do
     [] -> dieWithException verbosity SpecifyAnExecutable
     exe : args -> do
       (program, _) <- requireProgram verbosity (simpleProgram exe) programDb
-      let argOverrides =
+      let environmentPackageArgs =
             argsEquivalentOfGhcEnvironmentFile
               compiler
               (distDirLayout baseCtx)
@@ -201,21 +201,19 @@ execAction flags@NixStyleFlags{..} extraArgs globalFlags = do
             matchCompilerPath
               (elaboratedShared buildCtx)
               program
-          argOverrides' =
-            if envFilesSupported
-              || not programIsConfiguredCompiler
-              then []
-              else argOverrides
 
       ( if envFilesSupported
           then withTempEnvFile verbosity baseCtx buildCtx buildStatus
-          else \f -> f []
+          else \f ->
+            if programIsConfiguredCompiler
+              then f environmentPackageArgs []
+              else f [] []
         )
-        $ \envOverrides -> do
+        $ \argOverrides envOverrides -> do
           let program' =
                 withOverrides
                   envOverrides
-                  argOverrides'
+                  argOverrides
                   program
               invocation = programInvocation program' args
               dryRun =
@@ -253,7 +251,7 @@ withTempEnvFile
   -> ProjectBaseContext
   -> ProjectBuildContext
   -> PostBuildProjectStatus
-  -> ([(String, Maybe String)] -> IO a)
+  -> ([String] -> [(String, Maybe String)] -> IO a)
   -> IO a
 withTempEnvFile verbosity baseCtx buildCtx buildStatus action = do
   let tmpDirTemplate = distTempDirectory (distDirLayout baseCtx)
@@ -263,14 +261,14 @@ withTempEnvFile verbosity baseCtx buildCtx buildStatus action = do
     tmpDirTemplate
     "environment."
     ( \tmpDir -> do
-        envOverrides <-
-          createPackageEnvironment
+        (argOverrides, envOverrides) <-
+          createPackageEnvironmentAndArgs
             verbosity
             tmpDir
             (elaboratedPlanToExecute buildCtx)
             (elaboratedShared buildCtx)
             buildStatus
-        action envOverrides
+        action argOverrides envOverrides
     )
 
 -- | Get paths to all dependency executables to be included in PATH.
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs b/cabal-install/src/Distribution/Client/ProjectPlanOutput.hs
@@ -12,7 +12,7 @@ module Distribution.Client.ProjectPlanOutput
     -- | Several outputs rely on having a general overview of
   , PostBuildProjectStatus (..)
   , updatePostBuildProjectStatus
-  , createPackageEnvironment
+  , createPackageEnvironmentAndArgs
   , writePlanGhcEnvironment
   , argsEquivalentOfGhcEnvironmentFile
   ) where
@@ -777,7 +777,7 @@ writePackagesUpToDateCacheFile DistDirLayout{distProjectCacheFile} upToDate =
   writeFileAtomic (distProjectCacheFile "up-to-date") $
     Binary.encode upToDate
 
--- | Prepare a package environment that includes all the library dependencies
+-- | Prepare a package environment and args that includes all the library dependencies
 -- for a plan.
 --
 -- When running cabal new-exec, we want to set things up so that the compiler
@@ -786,14 +786,17 @@ writePackagesUpToDateCacheFile DistDirLayout{distProjectCacheFile} upToDate =
 -- temporarily, in case the compiler wants to learn this information via the
 -- filesystem, and returns any environment variable overrides the compiler
 -- needs.
-createPackageEnvironment
+--
+-- The function returns both the arguments you need to pass to the compiler and
+-- the environment variables you need to set.
+createPackageEnvironmentAndArgs
   :: Verbosity
   -> FilePath
   -> ElaboratedInstallPlan
   -> ElaboratedSharedConfig
   -> PostBuildProjectStatus
-  -> IO [(String, Maybe String)]
-createPackageEnvironment
+  -> IO ([String], [(String, Maybe String)])
+createPackageEnvironmentAndArgs
   verbosity
   path
   elaboratedPlan
@@ -808,14 +811,14 @@ createPackageEnvironment
               elaboratedShared
               buildStatus
           case envFileM of
-            Just envFile -> return [("GHC_ENVIRONMENT", Just envFile)]
+            Just envFile -> return (["-package-env=" ++ envFile], [("GHC_ENVIRONMENT", Just envFile)])
             Nothing -> do
               warn verbosity "the configured version of GHC does not support reading package lists from the environment; commands that need the current project's package database are likely to fail"
-              return []
+              return ([], [])
     | otherwise =
         do
           warn verbosity "package environment configuration is not supported for the currently configured compiler; commands that need the current project's package database are likely to fail"
-          return []
+          return ([], [])
 
 -- Writing .ghc.environment files
 --
diff --git a/changelog.d/pr-10828.md b/changelog.d/pr-10828.md
@@ -0,0 +1,15 @@
+---
+synopsis: "Isolate Cabal from the GHC_ENVIRONMENT variable"
+packages: [Cabal]
+prs: 10828
+
+issues: 10759
+---
+
+For GHC 8.4.4 and later, Cabal now passes the `-package-env=-` flag to GHC.
+This prevents the `GHC_ENVIRONMENT` variable or any package environment files
+from affecting Cabal builds.
+
+This change eliminates unexpected build behavior that could occur when users
+had GHC environment files configured in their system that Cabal wasn't aware
+of.
