Am Dienstag, den 07.06.2022, 14:22 +0000 schrieb Joseph Myers:
> On Tue, 7 Jun 2022, Martin Uecker wrote:
>
> > here is a preliminary patch the implements the proposed
> > tag compatibility rules for C23 in GCC (N2863). It works
>
> I don't see any response on the reflector to my comments on that proposal
> (message 21374, Fri, 14 Jan 2022 23:32:47 +0000). Nor do I see any tests
> in this patch dealing with the questions of exactly when struct and union
> types are complete or incomplete, as in my first comment there (if there
> are any tests concerning that, it's not apparent for lack of comments
> explaining what exactly the tests are trying to test). I think we'll need
> a version of the proposal without known issues before the patch is fully
> reviewable.
Thanks Joseph! I will revisit the wording next and then resend
the patch with the corresponing tests.
Martin
>
> > - the feature has a flag (-ftag-compat) which is now turned
> > on by default in all language modes to facilitate testing
> > and to identify backwards compatibility problems. Turned on,
> > it survives bootstrapping and regression testing with
> > only a few cases that test for diagnostics that go
> > away changed to turn it off.
>
> Turning on by default in past language modes seems questionable other than
> for this sort of preliminary testing (in any case, incompatible with
> previous standard requirements so can't be enabled for strict conformance
> modes).
> (And in general I'd discourage adding options for individual
> language feature like that, with the resulting proliferation of dialects
> with different combinations of features - again, it may be useful for
> testing purposes, especially before we know whether the feature gets into
> C23, and it may be useful within the compiler sources to distinguish in
> some way which places are checking for this feature rather than just
> testing flag_isoc2x, but actually releasing with a command-line option for
> it is more problematic.)
>
> > diff --git a/gcc/testsuite/gcc.dg/tag-compat2.c
> > b/gcc/testsuite/gcc.dg/tag-compat2.c
> > new file mode 100644
> > index 00000000000..20dc1a9c894
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tag-compat2.c
> > @@ -0,0 +1,47 @@
> > +/*
> > + * { dg-do compile }
> > + * { dg-options "-ftag-compat" }
> > + */
> > +
> > +typedef struct bar { int x; } X;
> > +typedef struct bar { float x; } Y; /* { dg-warning "redefinition of
> > struct or union" } */
>
> I'd expect conflicting definitions of a type in the same scope to remain
> errors, not warnings, regardless of this feature.
>
