Prevent -optc arguments from being duplicated in reverse order (#17471)wip/T17471

This reverts a part of commit
7bc5d6c6578ab9d60a83b81c7cc14819afef32ba that causes all arguments
to `-optc` (and `-optcxx`) to be passed twice to the C/C++ compiler,
once in reverse order and then again in the correct order. While
passing duplicate arguments is usually harmless it can cause breakage
in this pattern, which is employed by Hackage libraries in the wild:

```
ghc Foo.hs foo.c -optc-D -optcFOO
```

As `FOO -D -D FOO` will cause compilers to error.

Fixes #17471.

5 files changed, 22 insertions, 3 deletions

diff --git a/compiler/main/SysTools/Tasks.hs b/compiler/main/SysTools/Tasks.hs
index 5b0cb1cfa2..96a5b291da 100644
--- a/compiler/main/SysTools/Tasks.hs
+++ b/compiler/main/SysTools/Tasks.hs
@@ -127,10 +127,9 @@ runCc mLanguage dflags args = traceToolCommand dflags "cc" $ do
     Nothing -> ([], userOpts_c)
     Just language -> ([Option "-x", Option languageName], opts)
       where
-        s = settings dflags
         (languageName, opts) = case language of
-          LangC      -> ("c",             sOpt_c s ++ userOpts_c)
-          LangCxx    -> ("c++",           sOpt_cxx s ++ userOpts_cxx)
+          LangC      -> ("c",             userOpts_c)
+          LangCxx    -> ("c++",           userOpts_cxx)
           LangObjc   -> ("objective-c",   userOpts_c)
           LangObjcxx -> ("objective-c++", userOpts_cxx)
           LangAsm    -> ("assembler",     [])
diff --git a/testsuite/tests/ffi/should_run/T17471.hs b/testsuite/tests/ffi/should_run/T17471.hs
new file mode 100644
index 0000000000..bcaebc59cd
--- /dev/null
+++ b/testsuite/tests/ffi/should_run/T17471.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+module Main where
+
+import Foreign.C.Types
+
+foreign import ccall "foo" foo :: IO CInt
+
+main :: IO ()
+main = foo >>= print
diff --git a/testsuite/tests/ffi/should_run/T17471.stdout b/testsuite/tests/ffi/should_run/T17471.stdout
new file mode 100644
index 0000000000..d00491fd7e
--- /dev/null
+++ b/testsuite/tests/ffi/should_run/T17471.stdout
@@ -0,0 +1 @@
+1
diff --git a/testsuite/tests/ffi/should_run/T17471_c.c b/testsuite/tests/ffi/should_run/T17471_c.c
new file mode 100644
index 0000000000..64a9445a62
--- /dev/null
+++ b/testsuite/tests/ffi/should_run/T17471_c.c
@@ -0,0 +1,7 @@
+int foo() {
+#if defined(FOO)
+  return 1;
+#else
+  return 0;
+#endif
+}
diff --git a/testsuite/tests/ffi/should_run/all.T b/testsuite/tests/ffi/should_run/all.T
index d379191548..a0984a28fe 100644
--- a/testsuite/tests/ffi/should_run/all.T
+++ b/testsuite/tests/ffi/should_run/all.T
@@ -213,3 +213,6 @@ test('PrimFFIWord16', [omit_ways(['ghci'])], compile_and_run, ['PrimFFIWord16_c.
 test('T493', [omit_ways(['ghci'])], compile_and_run, ['T493_c.c'])
 
 test('UnliftedNewtypesByteArrayOffset', [omit_ways(['ghci'])], compile_and_run, ['UnliftedNewtypesByteArrayOffset_c.c'])
+
+test('T17471', [omit_ways(['ghci'])], compile_and_run,
+     ['T17471_c.c -optc-D -optcFOO'])