[Bug c++/99909] The value of 'std::is_integral_v<auto>' is not usable in a constant expression

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99909

--- 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:daa762f01d8cf932484b7df122a5e872439bc92c

commit r12-3950-gdaa762f01d8cf932484b7df122a5e872439bc92c
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Sep 28 17:26:20 2021 -0400

    c++: ttp matching with constrained auto parm [PR99909]

    Here, when unifying TT with S, processing_template_decl is unset, and
    this foils the dependence checks in do_auto_deduction for avoiding
    checking constraints on an auto when the initializer is dependent.

    This patch fixes this by making sure processing_template_decl is set
    around the call to unify from coerce_template_template_parms; this seems
    sensible because we're unifying one set of template parameters with
    another, so we're dealing with templated trees throughout.

            PR c++/99909

    gcc/cp/ChangeLog:

            * pt.c (coerce_template_template_parms): Keep
            processing_template_decl set around the call to unify as well.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-ttp3.C: New test.