Pass preprocessor options to C compiler when building foreign C files (#16737)

5 files changed, 54 insertions, 4 deletions

diff --git a/compiler/main/DriverPipeline.hs b/compiler/main/DriverPipeline.hs
index 59eb10ffd0..ffc11980e2 100644
--- a/compiler/main/DriverPipeline.hs
+++ b/compiler/main/DriverPipeline.hs
@@ -1190,9 +1190,6 @@ runPhase (RealPhase Cmm) input_fn dflags
 -----------------------------------------------------------------------------
 -- Cc phase
 
--- we don't support preprocessing .c files (with -E) now.  Doing so introduces
--- way too many hacks, and I can't say I've ever used it anyway.
-
 runPhase (RealPhase cc_phase) input_fn dflags
    | any (cc_phase `eqPhase`) [Cc, Ccxx, HCc, Cobjc, Cobjcxx]
    = do
@@ -1214,6 +1211,16 @@ runPhase (RealPhase cc_phase) input_fn dflags
               (includePathsQuote cmdline_include_paths)
         let include_paths = include_paths_quote ++ include_paths_global
 
+        -- pass -D or -optP to preprocessor when compiling foreign C files
+        -- (#16737). Doing it in this way is simpler and also enable the C
+        -- compiler to performs preprocessing and parsing in a single pass,
+        -- but it may introduce inconsistency if a different pgm_P is specified.
+        let more_preprocessor_opts = concat
+              [ ["-Xpreprocessor", i]
+              | not hcc
+              , i <- getOpts dflags opt_P
+              ]
+
         let gcc_extra_viac_flags = extraGccViaCFlags dflags
         let pic_c_flags = picCCOpts dflags
 
@@ -1223,7 +1230,7 @@ runPhase (RealPhase cc_phase) input_fn dflags
         -- hc code doesn't not #include any header files anyway, so these
         -- options aren't necessary.
         pkg_extra_cc_opts <- liftIO $
-          if cc_phase `eqPhase` HCc
+          if hcc
              then return []
              else getPackageExtraCcOpts dflags pkgs
 
@@ -1305,6 +1312,7 @@ runPhase (RealPhase cc_phase) input_fn dflags
                        ++ [ "-include", ghcVersionH ]
                        ++ framework_paths
                        ++ include_paths
+                       ++ more_preprocessor_opts
                        ++ pkg_extra_cc_opts
                        ))
 
diff --git a/testsuite/tests/driver/T16737.hs b/testsuite/tests/driver/T16737.hs
new file mode 100644
index 0000000000..daf830693b
--- /dev/null
+++ b/testsuite/tests/driver/T16737.hs
@@ -0,0 +1,32 @@
+{-# LANGUAGE TemplateHaskell #-}
+{-# OPTIONS_GHC -DFOO=2 -optP=-DBAR=3 -optc=-DBAZ=5 -optcxx=-DBAZ=7 #-}
+
+import Language.Haskell.TH.Syntax
+
+do
+  let code = unlines
+        [ "#if defined(__cplusplus)"
+        , "extern \"C\" {"
+        , "#endif"
+        , "#include <T16737.h>"
+        , "int FUN(void) {"
+        , "  return FOO * BAR * BAZ;"
+        , "}"
+        , "#if defined(__cplusplus)"
+        , "}"
+        , "#endif"
+        ]
+  addForeignSource LangC code
+  addForeignSource LangCxx code
+  pure []
+
+foreign import ccall unsafe "c_value"
+  c_value :: IO Int
+
+foreign import ccall unsafe "cxx_value"
+  cxx_value :: IO Int
+
+main :: IO ()
+main = do
+  print =<< c_value
+  print =<< cxx_value
diff --git a/testsuite/tests/driver/T16737.stdout b/testsuite/tests/driver/T16737.stdout
new file mode 100644
index 0000000000..8a3609b7ca
--- /dev/null
+++ b/testsuite/tests/driver/T16737.stdout
@@ -0,0 +1,2 @@
+30
+42
diff --git a/testsuite/tests/driver/T16737include/T16737.h b/testsuite/tests/driver/T16737include/T16737.h
new file mode 100644
index 0000000000..08c7ca8729
--- /dev/null
+++ b/testsuite/tests/driver/T16737include/T16737.h
@@ -0,0 +1,7 @@
+#pragma once
+
+#if defined(__cplusplus)
+#define FUN cxx_value
+#else
+#define FUN c_value
+#endif
diff --git a/testsuite/tests/driver/all.T b/testsuite/tests/driver/all.T
index 3cb0f95ce4..173ce3bf0a 100644
--- a/testsuite/tests/driver/all.T
+++ b/testsuite/tests/driver/all.T
@@ -270,3 +270,4 @@ test('inline-check', omit_ways(['hpc', 'profasm'])
 
 test('T14452', [], makefile_test, [])
 test('T15396', normal, compile_and_run, ['-package ghc'])
+test('T16737', [extra_files(['T16737include/'])], compile_and_run, ['-optP=-isystem -optP=T16737include'])