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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/102529] ctad for aliases fails in the presence of
 constraints
Date: Thu, 09 Mar 2023 15:28:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102529

--- 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 oth=
er
    than not deducing all the arguments; my implementation assumed that the
    right thing was to give up on the deduction guide.  But in consideratio=
n of
    CWG2664 this week I realized that we get a better result by just contin=
uing
    with an empty set of deductions, so the alias deduction guide is the sa=
me
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.=