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Subject: [Bug c++/98394] Concept with auto... template parameter pack in
 if-statement causes compilation error
Date: Tue, 09 Nov 2021 14:11:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98394

--- Comment #1 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:a22d910305a5232694ff48ead37a7f53e46b7202

commit r12-5053-ga22d910305a5232694ff48ead37a7f53e46b7202
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Nov 9 09:09:43 2021 -0500

    c++: bogus error w/ tentative type parse of concept-id [PR98394]

    Here when tentatively parsing the if condition as a declaration, we try
    to treat C<1> as the start of a constrained placeholder type, which we
    quickly reject because C doesn't accept a type as its first argument.
    But since we're parsing tentatively, we shouldn't emit an error in this
    case.

    In passing, also fix PR85846 by only overriding 'tentative' to false wh=
en
    given a concept-name, and not also when given a concept-id that has an
empty
    argument list.

            PR c++/98394
            PR c++/85846

    gcc/cp/ChangeLog:

            * parser.c (cp_parser_placeholder_type_specifier): Declare
            static.  Don't override tentative to false when tmpl is a
            concept-id with empty argument list.  Don't emit a "does not
            constrain a type" error when tentative.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-pr98394.C: New test.
            * g++.dg/cpp2a/concepts-pr85846.C: New test.=