GCC Bugzilla Bug 38161

#ifndef FOO
#define FOO sizeof(void *)
#elif FOO
#endif
t.c:3:7: error: missing binary operator before token "("

I expect it's caused by the fix to bug #36320.

According to my reading of the standard, this code is in fact incorrect.
This is basically the same as #36320.

I'm beginning to wonder, though, whether this change was overly eager on my
part
and should be made -pedantic only, or something like that.

Subject: Re:  [4.4 regression] #elif <non-const expression #defined in this
#if> breaks

Yes, I should have read the #36320 text more carefully.  I merely
noticed that its empty #elif cannot expand to anything correct, while
my example can (and does in the real-life case which produced it).

I thought C99 6.10p7 was what saved it:
  The preprocessing tokens within a preprocessing directive are
  not subject to macro expansion unless otherwise stated.
but maybe not.  6.10.1p3 doesn't say anything about some #elif branches
not being evaluated:-(  Hopefully that's just overly standard-lawerly
though.  Maybe comp.std.c would have been a better place to ask.

The standard talks about the groups controlled by conditionals being skipped.

There is no conditional controlling the #elif - it is at the top level - so I
see nothing permitting its non-evaluation.

*** This bug has been marked as a duplicate of 36453 ***