Adding an explicit pgmcxx flag for interaction with GHC

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

@@ -81,10 +81,10 @@ import Distribution.Types.GivenComponent
 import Distribution.Types.LocalBuildInfo
 import Distribution.Types.TargetInfo
 import Distribution.Types.UnitId
+import Distribution.Types.Version
 import Distribution.Utils.NubList (NubListR, toNubListR)
 import Distribution.Utils.Path
 import Distribution.Verbosity
-import Distribution.Version (Version)
 import Language.Haskell.Extension
 import System.Directory (listDirectory)
 import System.Environment (getEnv)
@@ -415,10 +415,19 @@ componentCxxGhcOptions verbosity lbi bi clbi odir filename =
                 MaximalDebugInfo -> ["-g3"]
              )
           ++ cxxOptions bi
-    , ghcOptCcProgram =
-        maybeToFlag $
-          programPath
-            <$> lookupProgram gccProgram (withPrograms lbi)
+    , -- Similarly, you need to add a split for cxx-sources in the configure script.
+      -- The configure split can be found here: https://github.com/haskell/cabal/pull/10844
+      ghcOptGppProgram =
+        ghcOptionsSince
+          (mkVersion [9, 4])
+          (compiler lbi)
+          (maybeToFlag $ programPath <$> lookupProgram gppProgram (withPrograms lbi))
+    , -- The assumption that the C++ compiler is part of the toolchain is only since ghc-9.4.
+      ghcOptCcProgram =
+        ghcOptionsBefore
+          (mkVersion [9, 4])
+          (compiler lbi)
+          (maybeToFlag $ programPath <$> lookupProgram gccProgram (withPrograms lbi))
     , ghcOptObjDir = toFlag odir
     , ghcOptExtra = hcOptions GHC bi
     }
@@ -482,6 +491,25 @@ componentJsGhcOptions verbosity lbi bi clbi odir filename =
     , ghcOptExtra = hcOptions GHC bi
     }
 
+-- Applies options only if the GHC version is greater than or
+-- equal to the given one.
+ghcOptionsSince :: Monoid a => Version -> Compiler -> a -> a
+ghcOptionsSince ver comp defOptions =
+  case compilerCompatVersion GHC comp of
+    Just v
+      | v >= ver -> defOptions
+      | otherwise -> mempty
+    Nothing -> mempty
+
+-- Applies options only if the GHC version is less than the given one.
+ghcOptionsBefore :: Monoid a => Version -> Compiler -> a -> a
+ghcOptionsBefore ver comp defOptions =
+  case compilerCompatVersion GHC comp of
+    Just v
+      | v < ver -> defOptions
+      | otherwise -> mempty
+    Nothing -> mempty
+
 componentGhcOptions
   :: VerbosityLevel
   -> LocalBuildInfo
@@ -555,6 +583,22 @@ componentGhcOptions verbosity lbi bi clbi odir =
         , -- Unsupported extensions have already been checked by configure
           ghcOptExtensions = toNubListR $ usedExtensions bi
         , ghcOptExtensionMap = Map.fromList . compilerExtensions $ (compiler lbi)
+        , -- Use -pgmc to ensure that Cabal always passes cc-options, ld-options to GHC (#4435, #9801)
+          -- We can only do this on GHC >= 9.4, as we need https://gitlab.haskell.org/ghc/ghc/-/merge_requests/6949
+          -- Without that GHC MR, this change would cause GHC to never pass -no-pie when linking,
+          -- which can cause breakage depending on the C toolchain use. We would have to appropriately
+          -- pass -pgmc-supports-no-pie as appropriate to avoid this regression.
+          ghcOptCcProgram =
+            ghcOptionsSince
+              (mkVersion [9, 4])
+              (compiler lbi)
+              (maybeToFlag $ programPath <$> lookupProgram gccProgram (withPrograms lbi))
+        , -- The assumption that the C++ compiler is part of the toolchain is only since ghc-9.4.
+          ghcOptGppProgram =
+            ghcOptionsSince
+              (mkVersion [9, 4])
+              (compiler lbi)
+              (maybeToFlag $ programPath <$> lookupProgram gppProgram (withPrograms lbi))
         }
   where
     exe_paths =

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

@@ -519,7 +519,10 @@ data GhcOptions = GhcOptions
   , ghcOptFfiIncludes :: NubListR FilePath
   -- ^ Extra header files to include for old-style FFI; the @ghc -#include@ flag.
   , ghcOptCcProgram :: Flag FilePath
-  -- ^ Program to use for the C and C++ compiler; the @ghc -pgmc@ flag.
+  -- ^ Program to use for the C compiler; the @ghc -pgmc@ flag and also
+  -- program to use for the C++ compiler before 9.4.
+  , ghcOptGppProgram :: Flag FilePath
+  -- ^ Program to use for the C++ compiler; the @ghc -pgmcxx@ flag.
   , ----------------------------
     -- Language and extensions
 
@@ -874,6 +877,7 @@ renderGhcOptions comp _platform@(Platform _arch os) opts
            in [cxxflag ++ opt | opt <- ghcOptCxxOptions opts]
         , ["-opta" ++ opt | opt <- ghcOptAsmOptions opts]
         , concat [["-pgmc", cc] | cc <- flag ghcOptCcProgram]
+        , concat [["-pgmcxx", cxx] | cxx <- flag ghcOptGppProgram]
         , -----------------
           -- Linker stuff
 

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/Main.hs

@@ -0,0 +1,16 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+module Main where
+
+import Foreign.C (CInt (..))
+
+foreign import ccall "pgmclib.h meaning_of_life_pgmc"
+  meaning_of_life_pgmc :: IO CInt
+
+main :: IO ()
+main = do
+  secret <- meaning_of_life_pgmc
+  -- The value 66 comes from __TESTOPT_PGMC__ - see cc-wrapper.sh.
+  if (secret == 66)
+    then putStrLn ("The secret is " ++ show secret)
+    else error ("Expected value 66, got " ++ show secret)

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/README.md

@@ -0,0 +1,7 @@
+# ForeignOptsPgmc
+
+This test case asserts that cabal passes the `-pgmc` GHC option to override the C compiler program.
+
+The cabal file sets `ghc-options: -pgmc scripts/cc-wrapper.sh`, pointing GHC at a shell script wrapper (`scripts/cc-wrapper.sh`) instead of the system C compiler. The wrapper adds `-D__TESTOPT_PGMC__=66` to every compilation and then delegates to the real `cc`. The C source requires `__TESTOPT_PGMC__` to be defined; if the wrapper is not used as the C compiler, the build fails with a `#error`.
+
+This test is skipped on Windows (no POSIX shell).

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/cabal.project

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

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/cabal.test.hs

@@ -0,0 +1,13 @@
+import Test.Cabal.Prelude
+
+main = do
+  skipIfWindows "requires a POSIX shell script as the C compiler wrapper"
+  -- Use -pgmc to ensure that Cabal always passes cc-options, ld-options to GHC (#4435, #9801)
+  -- We can only do this on GHC >= 9.4, as we need https://gitlab.haskell.org/ghc/ghc/-/merge_requests/6949
+  -- Without that GHC MR, this change would cause GHC to never pass -no-pie when linking,
+  -- which can cause breakage depending on the C toolchain use. We would have to appropriately
+  -- pass -pgmc-supports-no-pie as appropriate to avoid this regression.
+  cabalTest $ recordMode DoNotRecord $ do
+    skipUnlessGhcVersion ">= 9.4"
+    cabal "v2-build" ["foreign-opts-pgmc-exe"]
+    withPlan $ runPlanExe "foreign-opts-pgmc" "foreign-opts-pgmc-exe" []

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/cbits/pgmclib.c

@@ -0,0 +1,9 @@
+#include "pgmclib.h"
+
+#ifndef __TESTOPT_PGMC__
+#error "Did not get required __TESTOPT_PGMC__ from the -pgmc wrapper"
+#endif
+
+int meaning_of_life_pgmc() {
+    return __TESTOPT_PGMC__;
+}

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/cbits/pgmclib.h

@@ -0,0 +1,6 @@
+#ifndef PGMCLIB_H
+#define PGMCLIB_H
+
+int meaning_of_life_pgmc();
+
+#endif

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/foreign-opts-pgmc.cabal

@@ -0,0 +1,12 @@
+cabal-version:       2.2
+name:                foreign-opts-pgmc
+version:             0.1
+build-type:          Simple
+
+executable foreign-opts-pgmc-exe
+  main-is:             Main.hs
+  build-depends:       base
+  default-language:    Haskell2010
+  include-dirs:        cbits
+  c-sources:           cbits/pgmclib.c
+  ghc-options:         -pgmc scripts/cc-wrapper.sh

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmc/scripts/cc-wrapper.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+# Wrapper around cc that adds -D__TESTOPT_PGMC__=66 to every compilation.
+# Used by the ForeignOptsPgmc test to verify that -pgmc selects this wrapper.
+exec cc -D__TESTOPT_PGMC__=66 "$@"

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/Main.hs

@@ -0,0 +1,16 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+module Main where
+
+import Foreign.C (CInt (..))
+
+foreign import ccall "pgmcxxlib.h meaning_of_life_pgmcxx"
+  meaning_of_life_pgmcxx :: IO CInt
+
+main :: IO ()
+main = do
+  secret <- meaning_of_life_pgmcxx
+  -- The value 67 comes from __TESTOPT_PGMCXX__ - see cxx-wrapper.sh.
+  if (secret == 67)
+    then putStrLn ("The secret is " ++ show secret)
+    else error ("Expected value 67, got " ++ show secret)

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/README.md

@@ -0,0 +1,7 @@
+# ForeignOptsPgmcxx
+
+This test case asserts that cabal passes the `-pgmcxx` GHC option to override the C++ compiler program.
+
+The cabal file sets `ghc-options: -pgmcxx scripts/cxx-wrapper.sh`, pointing GHC at a shell script wrapper (`scripts/cxx-wrapper.sh`) instead of the system C++ compiler. The wrapper adds `-D__TESTOPT_PGMCXX__=67` to every compilation and then delegates to the real `g++`. The C++ source requires `__TESTOPT_PGMCXX__` to be defined; if the wrapper is not used as the C++ compiler, the build fails with a `#error`.
+
+This test is skipped on Windows (no POSIX shell).

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/cabal.project

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

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/cabal.test.hs

@@ -0,0 +1,9 @@
+import Test.Cabal.Prelude
+
+main = do
+  skipIfWindows "requires a POSIX shell script as the C++ compiler wrapper"
+  -- The assumption that the C++ compiler is part of the toolchain is only since ghc-9.4.
+  cabalTest $ recordMode DoNotRecord $ do
+    skipUnlessGhcVersion ">= 9.4"
+    cabal "v2-build" ["foreign-opts-pgmcxx-exe"]
+    withPlan $ runPlanExe "foreign-opts-pgmcxx" "foreign-opts-pgmcxx-exe" []

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/cxxbits/pgmcxxlib.cpp

@@ -0,0 +1,9 @@
+#include "pgmcxxlib.h"
+
+#ifndef __TESTOPT_PGMCXX__
+#error "Did not get required __TESTOPT_PGMCXX__ from the -pgmcxx wrapper"
+#endif
+
+int meaning_of_life_pgmcxx() {
+    return __TESTOPT_PGMCXX__;
+}

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/cxxbits/pgmcxxlib.h

@@ -0,0 +1,8 @@
+#ifndef PGMCXXLIB_H
+#define PGMCXXLIB_H
+extern "C" {
+
+int meaning_of_life_pgmcxx();
+
+}
+#endif

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/foreign-opts-pgmcxx.cabal

@@ -0,0 +1,15 @@
+cabal-version:       2.2
+name:                foreign-opts-pgmcxx
+version:             0.1
+build-type:          Simple
+
+executable foreign-opts-pgmcxx-exe
+  main-is:             Main.hs
+  build-depends:       base
+  default-language:    Haskell2010
+  include-dirs:        cxxbits
+  -- The following options can be ignore with -pgmcxx by default.
+  -- Only gcc need stdc++ for C++ code, g++ doesn't need it.
+  -- extra-libraries:     stdc++
+  cxx-sources:         cxxbits/pgmcxxlib.cpp
+  ghc-options:         -pgmcxx scripts/cxx-wrapper.sh

cabal-testsuite/PackageTests/FFI/ForeignOptsPgmcxx/scripts/cxx-wrapper.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+# Wrapper around g++ that adds -D__TESTOPT_PGMCXX__=67 to every compilation.
+# Used by the ForeignOptsPgmcxx test to verify that -pgmcxx selects this wrapper.
+exec g++ -D__TESTOPT_PGMCXX__=67 "$@"