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Subject: [Bug c++/97679] [10/11 Regression] [concepts] ICE with CTAD for a
 nested class template with constrained constructor
Date: Thu, 08 Apr 2021 17:10:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97679

--- Comment #3 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:05708d6eef87a3dd0c68b1aed7f8d9c3824062b8

commit r11-8064-g05708d6eef87a3dd0c68b1aed7f8d9c3824062b8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 8 13:07:37 2021 -0400

    c++: constrained CTAD for nested class template [PR97679]

    In the testcase below, we're crashing during constraint checking of the
    implicitly generated deduction guides for the nested class template A::B
    because we never substitute the outer template arguments (for A) into
    the constraint, neither ahead of time nor as part of satisfaction.

    Ideally we'd like to avoid substituting into a constraint ahead of
    time, but the "flattening" vector 'tsubst_args' is constructed under the
    assumption that all outer template arguments are already substituted in,
    and eliminating this assumption to yield a flattening vector that
    includes outer (generic) template arguments suitable for substituting
    into the constraint would be tricky and error-prone.  So this patch
    takes the approximate approach of substituting the outer arguments into
    the constraint ahead of time, so that the subsequent substitution of
    'tsubst_args' is coherent and so later satisfaction just works.

    gcc/cp/ChangeLog:

            PR c++/97679
            * pt.c (build_deduction_guide): Document OUTER_ARGS.  Substitute
            them into the propagated constraints.

    gcc/testsuite/ChangeLog:

            PR c++/97679
            * g++.dg/cpp2a/concepts-ctad3.C: New test.=