[Bug c++/106423] New: -Wc++20-compat diagnostics not suppressed by #pragma GCC diagnostic ignored

[Bug c++/106423] New: -Wc++20-compat diagnostics not suppressed by #pragma GCC diagnostic ignored

[tom at honermann dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106423

            Bug ID: 106423
           Summary: -Wc++20-compat diagnostics not suppressed by #pragma
                    GCC diagnostic ignored
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tom at honermann dot net
  Target Milestone: ---

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"
int constinit;

$ 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;
      |     ^~~~~~~~~

[Bug c++/106423] -Wc++20-compat diagnostics not suppressed by #pragma GCC diagnostic ignored

[tom at honermann dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106423

--- Comment #1 from Tom Honermann <tom at honermann dot net> ---
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.

[Bug c++/106423] -Wc++20-compat diagnostics not suppressed by #pragma GCC diagnostic ignored

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106423

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ville.voutilainen at gmail dot com
   Last reconfirmed|                            |2022-08-09
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

[Bug c++/106423] -Wc++20-compat diagnostics not suppressed by #pragma GCC diagnostic ignored

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106423

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:60468d6cd46a3bd3afe8ff856f82afcd4c65a217

commit r13-2081-g60468d6cd46a3bd3afe8ff856f82afcd4c65a217
Author: Tom Honermann <tom@honermann.net>
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
    case).

            PR c++/106423

    gcc/c-family/ChangeLog:
            * 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.

    gcc/cp/ChangeLog:
            * parser.cc (cp_lexer_saving_tokens): Add comment regarding
            diagnostic requirements.

    gcc/testsuite/ChangeLog:
            * g++.dg/cpp0x/keywords2.C: New test.
            * g++.dg/cpp2a/keywords2.C: New test.

    libcpp/ChangeLog:
            * include/cpplib.h (cpp_warning_reason): Add CPP_W_CXX20_COMPAT.
            * init.cc (cpp_create_reader): Add cpp_warn_cxx20_compat.