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We aren't able to parse __has_attribute (vendor::attr) (and __has_c_attribute and __has_cpp_attribute) in strict C < C23 modes. While in -std=gnu* modes or in -std=c23 there is CPP_SCOPE token, in -std=c* (except for -std=c23) there are is just a pair of CPP_COLON tokens. The c-lex.cc hunk adds support for that. That leads to a question if we should return 1 or 0 from __has_attribute (gnu::unused) or not, because while [[gnu::unused]] is parsed fine in -std=gnu*/-std=c23 modes (sure, with pedwarn for < C23), we do not parse it at all in -std=c* (except for -std=c23), we only parse [[__extension__ gnu::unused]] there. While the __extension__ in there helps to avoid the pedwarn, I think it is better to be consistent between GNU and strict C < C23 modes and parse [[gnu::unused]] too; on the other side, I think parsing [[__extension__ gnu : : unused]] is too weird and undesirable. So, the following patch adds a flag during preprocessing at the point where we normally create CPP_SCOPE tokens out of 2 consecutive colons on the first CPP_COLON to mark the consecutive case (as we are tight on the bits, I've reused the PURE_ZERO flag, which is used just by the C++ FE and only ever set (both C and C++) on CPP_NUMBER tokens, this new flag has the same value and is only ever used on CPP_COLON tokens) and instead of checking loose_scope_p argument (i.e. whether it is [[__extension__ ...]] or not), it just parses CPP_SCOPE or CPP_COLON with CLONE_SCOPE flag followed by another CPP_COLON the same. The latter will never appear in >= C23 or -std=gnu* modes, though guarding its use say with flag_iso && !flag_isoc23 && doesn't really work because the __extension__ case temporarily clears flag_iso flag. This makes the -std=c11 etc. behavior more similar to -std=gnu11 or -std=c23, the only difference I'm aware of are the #define JOIN2(A, B) A##B [[vendor JOIN2(:,:) attr]] [[__extension__ vendor JOIN2(:,:) attr]] cases, which are accepted in the latter modes, but results in error in -std=c11; but the error is during preprocessing that :: doesn't form a valid preprocessing token, which is true, so just don't do that if you try to have __STRICT_ANSI__ && __STDC_VERSION__ <= 201710L compatibility. 2024-02-22 Jakub Jelinek <jakub@redhat.com> PR c/114007 gcc/ * doc/extend.texi: (__extension__): Remove comments about scope tokens vs. two colons. gcc/c-family/ * c-lex.cc (c_common_has_attribute): Parse 2 CPP_COLONs with the first one with COLON_SCOPE flag the same as CPP_SCOPE. gcc/c/ * c-parser.cc (c_parser_std_attribute): Remove loose_scope_p argument. Instead of checking it, parse 2 CPP_COLONs with the first one with COLON_SCOPE flag the same as CPP_SCOPE. (c_parser_std_attribute_list): Remove loose_scope_p argument, don't pass it to c_parser_std_attribute. (c_parser_std_attribute_specifier): Adjust c_parser_std_attribute_list caller. gcc/testsuite/ * gcc.dg/c23-attr-syntax-6.c: Adjust testcase for :: being valid even in -std=c11 even without __extension__ and : : etc. not being valid anymore even with __extension__. * gcc.dg/c23-attr-syntax-7.c: Likewise. * gcc.dg/c23-attr-syntax-8.c: New test. libcpp/ * include/cpplib.h (COLON_SCOPE): Define to PURE_ZERO. * lex.cc (_cpp_lex_direct): When lexing CPP_COLON with another colon after it, if !CPP_OPTION (pfile, scope) set COLON_SCOPE flag on the first CPP_COLON token.
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