[Bug c++/102529] ctad for aliases fails in the presence of constraints

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102529

--- Comment #2 from CVS 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:afe1f0c251d0429069c2414d4f3f14042efc174f

commit r13-6556-gafe1f0c251d0429069c2414d4f3f14042efc174f
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 9 12:58:35 2023 -0800

    c++: CTAD for less-specialized alias template [PR102529]

    The standard was unclear what happens with the transformation of a
deduction
    guide if the initial template argument deduction fails for a reason other
    than not deducing all the arguments; my implementation assumed that the
    right thing was to give up on the deduction guide.  But in consideration of
    CWG2664 this week I realized that we get a better result by just continuing
    with an empty set of deductions, so the alias deduction guide is the same
as
    the original deduction guide plus the deducible constraint.

            DR 2664
            PR c++/102529

    gcc/cp/ChangeLog:

            * pt.cc (alias_ctad_tweaks): Continue after deduction failure.

    gcc/testsuite/ChangeLog:

            * g++.dg/DRs/dr2664.C: New test.
            * g++.dg/cpp2a/class-deduction-alias15.C: New test.