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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/115198] Class template argument deduction fails for copy
 ctor when used with an alias template if the aliased class template has
 explicitly defaulted copy ctor
Date: Tue, 25 Jun 2024 16:59:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115198

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:06ebb7c6f31fe42ffdea6f51ac1ba1f6b058c090

commit r15-1615-g06ebb7c6f31fe42ffdea6f51ac1ba1f6b058c090
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jun 25 12:59:24 2024 -0400

    c++: alias CTAD and copy deduction guide [PR115198]

    Here we're neglecting to update DECL_NAME during the alias CTAD guide
    transformation, which causes copy_guide_p to return false for the
    transformed copy deduction guide since DECL_NAME is still __dguide_C
    with TREE_TYPE C<B, T> but it should be __dguide_A with TREE_TYPE A<T>
    (i.e. C<false, T>).  This ultimately results in ambiguity during
    overload resolution between the copy deduction guide vs copy ctor guide.

    This patch makes us update DECL_NAME of a transformed guide accordingly
    during alias/inherited CTAD.

            PR c++/115198

    gcc/cp/ChangeLog:

            * pt.cc (alias_ctad_tweaks): Update DECL_NAME of the transformed
            guides.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/class-deduction-alias22.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>=