[cfe-dev] Unexpected warning in -std=gnu89 -pedantic mode.

[Douglas Gregor]

On Aug 26, 2009, at 5:12 AM, Enea Zaffanella wrote:
> There seems to be a problem in the handling of diagnostic for GNU
> extensions: some warnings are produced even though the -std=gnu89  
> option
> is specified.

We probably have quite a few of these problems, because many of these  
extension diagnostics were written before we distinguished between the  
different kinds of extensions (e.g., Microsoft vs. GNU), so they  
conflate "is an extension diagnostic" with "is a GNU extension.

> $ cat aaa.c
> int foo() {
>   return ({2+3;});
> }
>
> $ clang-cc -std=gnu89 -pedantic aaa.c
> aaa.c:2:11: warning: use of GNU statement expression extension
>   return ({2+3;});
>           ^
> 1 diagnostic generated.
> $

The fix for this issue would be to change 1311 of ParseExpr.cpp from

     Diag(Tok, diag::ext_gnu_statement_expr);

to

   if (!getLang().GNUMode)
     Diag(Tok, diag::ext_gnu_statement_expr);

> The same happens when using, e.g., __builtin_offsetof.

It'll happen in many places, all of which will need to be changed with  
a check for GNUMode (for GNU extensions). I'd be happy to review and  
apply such a patch, if someone feels like tackling this.

	- Doug