[Bug c++/110580] [14 Regression] gcc fails to typecheck nix-2.16.1 source: error: invalid initialization of reference of type

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110580

--- Comment #8 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:b76d71564925abcabe6f5ad61d904b23c682cdfb

commit r14-2433-gb76d71564925abcabe6f5ad61d904b23c682cdfb
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jul 11 10:05:19 2023 -0400

    c++: coercing variable template from current inst [PR110580]

    Here during ahead of time coercion of the variable template-id v1<int>,
    since we pass only the innermost arguments to coerce_template_parms (and
    outer arguments are still dependent at this point), substitution of the
    default template argument V=U just lowers U from level 2 to level 1 rather
    than replacing it with int as expected.  Thus after coercion we incorrectly
    end up with (effectively) v1<int, T> instead of v1<int, int>.

    Coercion of a class/alias template-id on the other hand always passes
    all levels arguments, which avoids this issue.  So this patch makes us
    do the same for variable template-ids.

            PR c++/110580

    gcc/cp/ChangeLog:

            * pt.cc (lookup_template_variable): Pass all levels of arguments
            to coerce_template_parms, and use the parameters from the most
            general template.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/var-templ83.C: New test.