On 7/14/26 1:52 PM, Jakub Jelinek wrote:
Hi!
Apparently in clang __clang__ is a predefined macro (predefined to 1).
Because of that, clang doesn't have alternate spelling of its scoped
attributes as
[[__clang__::__something__]]
but
[[_Clang::__something__]]
The former isn't accepted even with -U__clang__.
For GNU attributes they do handle
[[__gnu__::__something__]]
like GCC does (if they support a particular attribute).
So, I'm afraid if we want to stay compatible with this mess, we need
to do the same thing.
The following patch does that.
It emits a warning when one attempts to use the __clang__ attribute
namespace suggesting to use _Clang instead (clang++ does that too),
but in __has_cpp_attribute/__has_attribute doesn't do that, just ensures
that 0 is returned in that case (i.e. it is not canonicalized in that
case), just canonicalizes _Clang to clang.
Ok for trunk if this passes full bootstrap/regtest?
2026-07-14 Jakub Jelinek <[email protected]>
PR c++/120635
gcc/
* doc/extend.texi: Document variant spelling of
standard attributes and that alternate namespace
spelling for clang namespace is _Clang rather
than __clang__. For no_specializations use
_Clang:: rather than __clang__::.
gcc/c-family/
* c-lex.cc (c_common_has_attribute): For __clang__
namespace don't call canonicalize_attr_name and for
_Clang use clang instead.
gcc/cp/
* parser.cc (cp_parser_std_attribute): Add
canonicalize_attr_ns_name lambda and use it instead of
canonicalize_attr_name for namespaces. Emit a warning
on __clang__::.
(cp_parser_std_attribute_spec): Emit a warning on
using __clang__:.
gcc/testsuite/
* g++.dg/cpp0x/attr-trivial_abi8.C: Add further tests.
* g++.dg/cpp0x/attr-trivial_abi11.C: New test.
* g++.dg/ext/attr-no_specializations1.C: Use _Clang:: instead of
__clang__.
* g++.dg/ext/attr-no_specializations2.C: Likewise.
* g++.dg/ext/attr-no_specializations6.C: Likewise.
* g++.dg/ext/attr-no_specializations7.C: Likewise.
* g++.dg/ext/attr-no_specializations8.C: Likewise.
* g++.dg/ext/attr-no_specializations10.C: Add further tests.
* g++.dg/ext/attr-no_specializations12.C: New test.
--- gcc/doc/extend.texi.jj 2026-07-13 18:37:33.605239738 +0200
+++ gcc/doc/extend.texi 2026-07-14 19:08:44.872456333 +0200
@@ -1821,9 +1821,15 @@ entity is ignored with a warning.
Every GNU-specific attribute has an alternate name that is prefixed
and suffixed by two underscores; for example, the alternate name of
-@code{weak} is @code{__weak__}. These alternate names are useful in
-library header files in case they are included into files that have
+@code{weak} is @code{__weak__}. These alternate names are useful in library
+header files in case they are included into files that have
This rewrapping seems unnecessary.
redefined the base name of the attribute as a preprocessor macro.
+Similarly for every supported standard or scoped attribute, for example, the
+variant spellings of @code{[[gnu::weak]]} are @code{[[__gnu__::__weak__]]},
+@code{[[gnu::__weak__]]} or @code{[[__gnu__::weak]]}. The only exception
+is that alternate spelling of the @code{clang} scoped attribute namespace
+is @code{_Clang} rather than @code{__clang__} for compatibility with that
+compiler.
GCC also accepts the keyword @code{__attribute} as a synonym for
@code{__attribute__}.
@@ -33311,6 +33312,16 @@ cp_parser_std_attribute (cp_parser *pars
cp_lexer_consume_token (parser->lexer);
token = cp_lexer_peek_token (parser->lexer);
+ auto canonicalize_attr_ns_name = [] (tree attr_ns) {
{ on next line.
OK with those tweaks.
Jason
