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.
> - 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.
--
Joseph S. Myers
jos...@codesourcery.com
