[Bug c++/122819] Linkage of temploid friends attached to named modules

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122819

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Nathaniel Shead <nshead@gcc.gnu.org>:

https://gcc.gnu.org/g:ffd34b63c2c2c9f0f928d8da26df729eef50db20

commit r16-6372-gffd34b63c2c2c9f0f928d8da26df729eef50db20
Author: Nathaniel Shead <nathanieloshead@gmail.com>
Date:   Sun Dec 7 23:17:15 2025 +1100

    c++: Non-inline temploid friends should still be COMDAT [PR122819]

    Modules allow temploid friends to no longer be implicitly inline, as
    functions defined in a class body will not be implicitly inline if
    attached to a named module.

    This requires us to clean up linkage handling a little bit, mostly by
    replacing usages of 'DECL_TEMPLATE_INSTANTIATION' with
    'DECL_TEMPLOID_INSTANTIATION' when determining if an entity has vague
    linkage.

    This caused the friend88.C testcase to miscompile however, as 'foo' was
    incorrectly having 'DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION' getting
    set because it was keeping its tinfo.

    This is because 'non_templated_friend_p' was returning 'false', since
    the function didn't have a primary template.  But that's expected I
    think here, so fixed by also returning true for friend declarations
    pushed into namespace scope, which still allows dependent nested friends
    to be considered templated.

            PR c++/122819

    gcc/cp/ChangeLog:

            * decl.cc (start_preparsed_function): Use
            DECL_TEMPLOID_INSTANTIATION instead of
            DECL_TEMPLATE_INSTANTIATION to check vague linkage.
            * decl2.cc (vague_linkage_p): Likewise.
            (c_parse_final_cleanups): Simplify condition.
            * pt.cc (non_templated_friend_p): Namespace-scope friend
            function declarations without a primary template are still
            non-templated.
            * semantics.cc (expand_or_defer_fn_1): Also check for temploid
            friend functions.

    gcc/testsuite/ChangeLog:

            * g++.dg/modules/tpl-friend-22.C: New test.
            * g++.dg/template/friend88.C: New test.

    Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
    Reviewed-by: Jason Merrill <jason@redhat.com>