[Bug c++/109653] [[clang::fallthrough]] recognised up to g++ v12 not not g++ v13

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109653

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Hmm, __has_cpp_attribute never returns 0 for unknown attributes
> 
> #if defined __has_cpp_attribute 
> #  if __has_cpp_attribute (fakeattribute)
> #    error errorout
> #  endif
> #endif
> 
> I thought it should.

Never mind, it does.

This is how you are supposed to use attributes:
#if defined __has_cpp_attribute 
#  if __has_cpp_attribute (clang::fallthrough)
#   define f [[clang::fallthrough]]
#  elif __has_cpp_attribute (gnu::fallthrough)
#   define f [[gnu::fallthrough]]
#  elif  __has_cpp_attribute (fallthrough)
#   define f [[fallthrough]]
# endif
#endif

#ifndef f
#define f
#endif


#include <cstdio>

int main (int argc, char* argv[])
{
    switch(argc)
    {
    case 0:
        printf("%s\n", argv[1]);
        f;
    default:
        printf("%d args\n", argc);
    }

    return 0;
}