As demonstrated at https://godbolt.org/z/GoTqPTcM3, use of gcc's '#pragma GCC diagnostic ignored "-Wc++20-compat"' directive fails to suppress -Wc++20-compat enabled diagnostics. gcc versions 10 and up are affected.
$ cat t.cpp
#pragma GCC diagnostic ignored "-Wc++20-compat"
$ gcc -c -std=c++17 -Wc++20-compat t.cpp
t.cpp:2:5: warning: identifier ‘constinit’ is a keyword in C++20 [-Wc++20-compat]
2 | int constinit;
A patch for this issue was submitted to the gcc-patches mailing list and is available at https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598736.html.
The master branch has been updated by Jason Merrill <firstname.lastname@example.org>:
Author: Tom Honermann <email@example.com>
Date: Mon Aug 1 14:49:00 2022 -0400
c++: Fix pragma suppression of -Wc++20-compat diagnostics [PR106423]
Gcc's '#pragma GCC diagnostic' directives are processed in "early mode"
(see handle_pragma_diagnostic_early) for the C++ frontend and, as such,
require that the target diagnostic option be enabled for the preprocessor
(see c_option_is_from_cpp_diagnostics). This change modifies the
-Wc++20-compat option definition to register it as a preprocessor option
so that its associated diagnostics can be suppressed. The changes also
implicitly disable the option in C++20 and later modes. These changes
are consistent with the definition of the -Wc++11-compat option.
This support is motivated by the need to suppress the following diagnostic
otherwise issued in C++17 and earlier modes due to the char8_t typedef
present in the uchar.h header file in glibc 2.36.
warning: identifier âchar8_tâ is a keyword in C++20 [-Wc++20-compat]
Tests are added to validate suppression of both -Wc++11-compat and
-Wc++20-compat related diagnostics (fixes were only needed for the C++20
* c-opts.cc (c_common_post_options): Disable -Wc++20-compat
diagnostics in C++20 and later.
* c.opt (Wc++20-compat): Enable hooks for the preprocessor.
* parser.cc (cp_lexer_saving_tokens): Add comment regarding
* g++.dg/cpp0x/keywords2.C: New test.
* g++.dg/cpp2a/keywords2.C: New test.
* include/cpplib.h (cpp_warning_reason): Add CPP_W_CXX20_COMPAT.
* init.cc (cpp_create_reader): Add cpp_warn_cxx20_compat.
I believe this issue can be resolved as fixed via commit 60468d6cd46a3bd3afe8ff856f82afcd4c65a217 for the gcc 13 release.
(In reply to Tom Honermann from comment #3)
> I believe this issue can be resolved as fixed via commit
> 60468d6cd46a3bd3afe8ff856f82afcd4c65a217 for the gcc 13 release.
Yes, it's normal procedure that the bz will be closed as fixed once the patches have been merged, it's just a separate step.