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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug preprocessor/114007] gcc chokes on
 __has_cpp_attribute(clang::unsafe_buffer_usage)
Date: Wed, 21 Feb 2024 14:26:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114007

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Sandiford from comment #14)
> I might have misunderstood the suggestion and so be arguing against
> something that no-one is suggesting, but I think [[__extension__ =E2=80=
=A6]] should
> accept the same things for all standard versions (C23, pre-C23, and GNU).=
=20
> It was intended to be something that header files and macros could use
> without needing to be sensitive to the user's choice of standard.

That is still the case of [[__extension__ arm::streaming]] and similar.
The only thing in the suggestion that would be only sometimes allowed would=
 be
[[__extension__ arm: :streaming]]
(or [[__extension__ arm:/**/:streaming]] etc.
which I'd hope nobody is planning to use in the header files.
Basically, with the flag_iso && !flag_isoc23 modes, :: is not one token but=
 2,
and while we in some cases could look at location info if they are adjacent=
 in
the source, if column info isn't accurate (too long lines or too many lines)
that information is lost.
Or of course if you'd strongly like to accept [[__extension__ arm: :streami=
ng]]
in all language modes (but it won't be accepted in C++ anyway), I'd at least
like to see accepting [[arm::streaming]] in the flag_iso && !flag_isoc23 mo=
des
(with the usual pedwarn).
If we only wanted adjacent ::s and nothing in between, perhaps the preproce=
ssor
could set some flag on one of the CPP_COLONs (or both) if otherwise for
CPP_OPTION (pfile, scope) it would be creating CPP_SCOPE, and check that fl=
ag
during attribute and __has*attribute parsing?=