[Bug c++/122509] Base template class name lookup only with qualified names

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122509

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:d19b95ca96f2e10732007d9cd59e6430df8d0b2a

commit r16-6274-gd19b95ca96f2e10732007d9cd59e6430df8d0b2a
Author: Egas Ribeiro <egas.g.ribeiro@gmail.com>
Date:   Sat Dec 13 20:06:09 2025 +0000

    c++: Fix injected-class-name lookup with multiple bases [PR122509]

    When looking up an unqualified injected-class-name in a member access
    expression (e.g., D().v<int>), cp_parser_lookup_name calls lookup_member
    with protect=0, causing it to return NULL on ambiguity instead of the
    candidate list. This prevented the existing DR 176 logic in
    maybe_get_template_decl_from_type_decl from resolving the ambiguity.

    Per DR 176, if all ambiguous candidates are instantiations of the same
    class template and the name is followed by a template-argument-list,
    the reference is to the template itself and is not ambiguous.

    Fix by using protect=2 to return the ambiguous candidate list.

            PR c++/122509

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_lookup_name): Use protect=2 instead of
            protect=0 when calling lookup_member.

    gcc/testsuite/ChangeLog:

            * g++.dg/tc1/dr176-2.C: New test.

    Signed-off-by: Egas Ribeiro <egas.g.ribeiro@gmail.com>
    Reviewed-by: Jason Merrill <jason@redhat.com>