[Bug c++/94645] [10 Regression][concepts] incorrect concept evaluation with decltype, plus internal error since r10-7554-gf1ad7bac76b66257

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94645

--- Comment #11 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:f9f166251f181ddcee64092d89aecbc1166ca706

commit r10-7932-gf9f166251f181ddcee64092d89aecbc1166ca706
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 23 17:29:55 2020 -0400

    c++: Lambda in friend of constrained class [PR94645]

    In the testcase below, when grokfndecl processes the operator() decl for
the
    lambda inside the friend function foo, processing_template_decl is rightly
1,
    but template_class_depth on the lambda's closure type incorrectly returns 0
    instead of 1.

    Since processing_template_decl > template_class_depth, this makes
grokfndecl
    think that the operator() has its own set of template arguments, and so we
    attach the innermost set of constraints -- those belonging to struct l --
to the
    operator() decl.  We then get confused when checking
constraints_satisfied_p on
    the operator() because it doesn't have template information and yet has
    constraints associated with it.

    This patch fixes template_class_depth to return the correct template
nesting
    level in cases like these, in that when it hits a friend function it walks
into
    the DECL_FRIEND_CONTEXT of the friend rather than into the CP_DECL_CONTEXT.

    gcc/cp/ChangeLog:

            PR c++/94645
            * pt.c (template_class_depth): Walk into the DECL_FRIEND_CONTEXT of
a
            friend declaration rather than into its CP_DECL_CONTEXT.

    gcc/testsuite/ChangeLog:

            PR c++/94645
            * g++.dg/cpp2a/concepts-lambda6.C: New test.