[Bug c++/53431] C++ preprocessor ignores #pragma GCC diagnostic

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53431

--- Comment #51 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Lewis Hyatt <lhyatt@gcc.gnu.org>:

https://gcc.gnu.org/g:e46f4d7430c5210465791603735ab219ef263c51

commit r13-1544-ge46f4d7430c5210465791603735ab219ef263c51
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Tue Jul 5 17:15:28 2022 -0400

    diagnostics: Honor #pragma GCC diagnostic in the preprocessor [PR53431]

    As discussed on PR c++/53431, currently, "#pragma GCC diagnostic" does
    not always take effect for diagnostics generated by libcpp. The reason
    is that libcpp itself does not interpret this pragma and only sends it on
    to the frontend, hence the pragma is only honored if the frontend
    arranges for it. The C frontend does process the pragma immediately
    (more or less) after seeing the token, so things work fine there. The PR
    points out that it doesn't work for C++, because the C++ frontend
    doesn't handle anything until it has read all the tokens from
    libcpp. The underlying problem is not C++-specific, though, and for
    instance, gcc -E has the same issue.

    This commit fixes the PR by adding the concept of an early pragma handler
that
    can be registered by frontends, which gives them a chance to process
    diagnostic pragmas from libcpp before it is too late for them to take
    effect. The C++ and preprocess-only frontends are modified to use early
    pragmas and correct the behavior.

    gcc/c-family/ChangeLog:

            PR preprocessor/53920
            PR c++/53431
            * c-common.cc (c_option_is_from_cpp_diagnostics): New function.
            * c-common.h (c_option_is_from_cpp_diagnostics): Declare.
            (c_pp_stream_token): Declare.
            * c-ppoutput.cc (init_pp_output): Refactor logic about skipping
            pragmas to...
            (should_output_pragmas): ...here. New function.
            (token_streamer::stream): Support handling early pragmas.
            (do_line_change): Likewise.
            (c_pp_stream_token): New function.
            * c-pragma.cc (struct pragma_diagnostic_data): New helper class.
            (pragma_diagnostic_lex_normal): New function. Moved logic for
            interpreting GCC diagnostic pragmas here.
            (pragma_diagnostic_lex_pp): New function for parsing diagnostic
pragmas
            directly from libcpp.
            (handle_pragma_diagnostic): Refactor into helper function...
            (handle_pragma_diagnostic_impl): ...here.  New function.
            (handle_pragma_diagnostic_early): New function.
            (handle_pragma_diagnostic_early_pp): New function.
            (struct pragma_ns_name): Renamed to...
            (struct pragma_pp_data): ...this.  Add new "early_handler" member.
            (c_register_pragma_1): Support early pragmas in the preprocessor.
            (c_register_pragma_with_early_handler): New function.
            (c_register_pragma): Support the new early handlers in struct
            internal_pragma_handler.
            (c_register_pragma_with_data): Likewise.
            (c_register_pragma_with_expansion): Likewise.
            (c_register_pragma_with_expansion_and_data): Likewise.
            (c_invoke_early_pragma_handler): New function.
            (c_pp_invoke_early_pragma_handler): New function.
            (init_pragma): Add early pragma support for diagnostic pragmas.
            * c-pragma.h (struct internal_pragma_handler): Add new early
handler
            members.
            (c_register_pragma_with_early_handler): Declare.
            (c_invoke_early_pragma_handler): Declare.
            (c_pp_invoke_early_pragma_handler): Declare.

    gcc/cp/ChangeLog:

            PR c++/53431
            * parser.cc (cp_parser_pragma_kind): Move earlier in the file.
            (cp_lexer_handle_early_pragma): New function.
            (cp_lexer_new_main): Support parsing and handling early pragmas.
            (c_parse_file): Adapt to changes in cp_lexer_new_main.

    gcc/testsuite/ChangeLog:

            PR preprocessor/53920
            PR c++/53431
            * c-c++-common/pragma-diag-11.c: New test.
            * c-c++-common/pragma-diag-12.c: New test.
            * c-c++-common/pragma-diag-13.c: New test.