[cfe-dev] [llvm-dev] problem (and fix) with -fms-extensions

[Marc Espie via cfe-dev]

On Fri, May 12, 2017 at 08:53:53AM -0700, Reid Kleckner wrote:
> 
>    Moving to cfe-dev to discuss clang things.
>    I think we already have _WCHAR_T_DEFINED for this:
>    Â  if (LangOpts.MicrosoftExt) {
>    Â  Â  if (LangOpts.WChar) {
>    Â  Â  Â  // wchar_t supported as a keyword.
>    Â  Â  Â  Builder.defineMacro("_WCHAR_T_DEFINED");
>    Â  Â  Â  Builder.defineMacro("_NATIVE_WCHAR_T_DEFINED");
>    Â  Â  }
>    Â  }

Nope. I'm talking about the __wchar_t type.
In my case, even a C language "hello world" won't compile:

nausicaa$ clang -fms-extensions a.c
In file included from a.c:1:
In file included from /usr/include/stdio.h:43:
In file included from /usr/include/sys/_types.h:37:
/usr/include/machine/_types.h:132:15: error: cannot combine with previous 'int'
      declaration specifier
typedef int                     __wchar_t;
                                ^
1 error generated.

but actually based on the existing code, I would suggest following
the pattern. 

my main concern would be: are names with ___ readable, or is there
a suggestion for better names ?

Index: InitPreprocessor.cpp
===================================================================
RCS file: /cvs/src/gnu/llvm/tools/clang/lib/Frontend/InitPreprocessor.cpp,v
retrieving revision 1.1.1.4
diff -u -p -r1.1.1.4 InitPreprocessor.cpp
--- InitPreprocessor.cpp	14 Mar 2017 08:07:56 -0000	1.1.1.4
+++ InitPreprocessor.cpp	13 May 2017 15:59:14 -0000
@@ -666,6 +668,10 @@ static void InitializePredefinedMacros(c
       // wchar_t supported as a keyword.
       Builder.defineMacro("_WCHAR_T_DEFINED");
       Builder.defineMacro("_NATIVE_WCHAR_T_DEFINED");
+    } else {
+      // __wchar_t supported as a keyword
+      Builder.defineMacro("___WCHAR_T_DEFINED");
+      Builder.defineMacro("_NATIVE___WCHAR_T_DEFINED");
     }
   }