Doesn't allow incomplete type in member access

[RealLitb]

Bugzilla Link	9471
Version	trunk
OS	Linux

Extended Description

Clang does not conform to the C Standard, it appears (GCC doesn't either):

struct A {
int a;
int x : (sizeof ((struct A*)0)->a * 8);
};

C doesn't forbid the left operand to be a pointer to incomplete type. The only requirement it has is that it's a pointer to a structure type, and that the right operand shall name a member of that structure. Both conditions are satisfied (C99: 6.5.2.3p2 and 6.2.1p7).

[AaronBallman]

No C compiler accepts this code: https://godbolt.org/z/o677Tb1nh

I think this is either a defect in the C standard or there's a constraint I've yet to find covering this. I've raised the question on the WG14 reflectors.

[AaronBallman]

The general consensus position on the reflectors (but not an official committee poll) is that this was never intended to work and that the standard should be clarified. You can currently squint at the standard as already making this a constraint violation because a structure has no members until the structure is complete, but that's a far too subtle reading.

Closing this issue as invalid, and I'll write a quick paper to clarify the wording in the standard.