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

1 files changed, 12 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
                        ))