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Subject: [Bug c++/92103] constraints not checked on nested class template
Date: Wed, 03 Jun 2020 20:41:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92103

--- Comment #4 from CVS 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:aee69073cdb8086d393f12474c6177e75467ceaa

commit r11-884-gaee69073cdb8086d393f12474c6177e75467ceaa
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jun 3 16:40:28 2020 -0400

    c++: constrained nested partial specialization [PR92103]

    When determining the most specialized partial specialization of a
    primary template that is nested inside a class template, we first
    tsubst the outer template arguments into the TEMPLATE_DECL of each
    partial specialization, and then check for satisfaction of each of the
    new TEMPLATE_DECL's constraints.

    But tsubst_template_decl does not currently guarantee that constraints
    from the original DECL_TEMPLATE_RESULT get reattached to the new
    DECL_TEMPLATE_RESULT.  In the testcase below, this leads to the
    constraints_satisfied_p check in most_specialized_partial_spec to
    trivially return true for each of the partial specializations.

    I'm not sure if such a guarantee would be desirable, but in this case we
    can just check constraints_satisfied_p on the original TEMPLATE_DECL
    instead of on the tsubsted TEMPLATE_DECL here, which is what this patch
    does (alongside some reorganizing).

    gcc/cp/ChangeLog:

            PR c++/92103
            * pt.c (most_specialized_partial_spec): Reorganize the loop over
            DECL_TEMPLATE_SPECIALIZATIONS.  Check constraints_satisfied_p on
            the original template declaration, not on the tsubsted one.

    gcc/testsuite/ChangeLog:

            PR c++/92103
            * g++.dg/cpp2a/concepts-partial-spec7.C: New test.=