[Bug c/14374] New: valid unamed struct in a union rejected by gcc

[ahs3 at fc dot hp dot com]

If I understand the C standard, section 6.2.5, para 20, on union types
correctly, the following is valid C:

struct a {
   int i;
};

struct b {
   long l;
};

typedef union {
   struct a;
   struct b;
} MD;

int main ()
{
   MD md;
   return 0;
}


When compiled with gcc prior to 3.3, the code is accepted as valid.  When
compiled with 3.3 or later versions, the compiler issues the following error:

junk2.c:11: warning: declaration does not declare anything
junk2.c:12: warning: declaration does not declare anything

These line numbers point to the unnamed structs within the union.  This seems to
be related to previously closed bugs #6660, #8420 and #10225.  If one uses the
-fms-extensions-switch as suggested in #10225, the code does compile.  However,
I think this is valid c99 code, and not just a microsoft extension.

If a language lawyer can show me where these semantics are prohibited, then this
is invalid code; if a language lawyer cannot find the prohibition, then gcc
needs to revert to prior behavior and accept this code.

Thanks in advance for any clarification.

-- 
           Summary: valid unamed struct in a union rejected by gcc
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ahs3 at fc dot hp dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: ia64-unknown-linux-gnu
  GCC host triplet: ia64-unknown-linux-gnu
GCC target triplet: ia64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14374