[Bug c++/101677] [11/12 Regression] Concept with use of incomplete type succeeds on GCC 10.3.0, fails on GCC 11 onward

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101677

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:1de6612d994ada8edaab18bbc6afd8e9a57413aa

commit r12-7997-g1de6612d994ada8edaab18bbc6afd8e9a57413aa
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Mar 27 22:31:51 2022 -0400

    c++: elaborated-type-spec in requires-expr [PR101677]

    We were failing to declare class S in the global namespace because we were
    treating the requires-expression parameter scope as a normal block scope,
so
    the implicit declaration went there.

    It seems to me that the requires parameter scope is more like a function
    parameter scope (not least in the use of the word "parameter"), so let's
    change the scope kind.  But then we need to adjust the prohibition on
    placeholders declaring implicit template parameters.

            PR c++/101677

    gcc/cp/ChangeLog:

            * name-lookup.h (struct cp_binding_level): Add requires_expression
            bit-field.
            * parser.cc (cp_parser_requires_expression): Set it.
            (synthesize_implicit_template_parm): Check it.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-pr67178.C: Adjust error.
            * g++.dg/cpp2a/concepts-requires28.C: New test.