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

[Reid Kleckner via cfe-dev]

I'd rather not add new pre-defined macros if we can avoid it. There are
already too many. You can probably detect this situation with:
#if defined(_MSC_EXTENSIONS) && !defined(_WCHAR_T_DEFINED)

On Sat, May 13, 2017 at 9:02 AM, Marc Espie <espie at nerim.net> wrote:

> 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");
>      }
>    }
>
>
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