[Bug c++/123825] std::meta::has_identifier issue

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123825

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:d6386e0984556173339c06b2b7cfe2dd55eeb07b

commit r16-7212-gd6386e0984556173339c06b2b7cfe2dd55eeb07b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jan 31 10:19:26 2026 +0100

    c++: Handle argument merging push_local_extern_decl_alias [PR123825]

    The first testcase comes directly from
    https://eel.is/c++draft/meta.reflection#names-1.8.2
    and shows that we don't handle for -freflection the function
    argument name difference handling isn't performed for local externs,
    which doesn't go the duplicate_decls route but directly remembers
    the alias.
    The following patch handles outlines the DECL_ARGUMENTS handling
    from duplicate_decls and uses it in push_local_extern_decl_alias
    (with some minor differences and for now not propagating attributes
    back for the push_local_extern_decl_alias case unless -freflection).

    ALso, I found that the addition of a new alias created completely broken
    DECL_ARGUMENTS (copied at most the first PARM_DECL, never more than that).
    That is because copy_decl clears DECL_CHAIN, so the loop always stopped
    after the first iteration.

    2026-01-31  Jakub Jelinek  <jakub@redhat.com>

            PR c++/123825
            * cp-tree.h (merge_decl_arguments): Declare.
            * decl.cc (duplicate_decls): Outline DECL_ARGUMENTS handling
            into ...
            (merge_decl_arguments): ... new function.
            * name-lookup.cc (push_local_extern_decl_alias): Call
            merge_decl_arguments.  Don't copy just the first PARM_DECL when
            creating a new alias FUNCTION_DECL.

            * g++.dg/reflect/has_identifier3.C: New test.
            * g++.dg/reflect/identifier_of3.C: New test.
            * g++.dg/cpp26/attr-indeterminate5.C: New test.