[Bug c++/86193] [DR455] Partial ordering of non-type template parameters with dependent types

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86193

--- Comment #4 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:288e4c64f6b4806358aabc9b99b2fba72bf04bf6

commit r12-8256-g288e4c64f6b4806358aabc9b99b2fba72bf04bf6
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Apr 25 21:46:56 2022 -0400

    c++: partial ordering with dependent NTTP type [PR105289]

    Here ever since r11-6483-ge2e2f3f2c9400f we're rejecting and crashing
    on (respectively) two testcases that we used to accept in C++17 mode
    since r8-1437-g3da557ec145823.  Both testcases declare a partial
    specialization of a primary template that has an NTTP with dependent
    type, and the validity of these partial specializations is unclear and
    the subject of PR86193 / CWG 455.

    So for now, this minimal patch just aims to fix the crash in the second
    testcase.  During deduction, when checking whether the type of an NTTP
    uses still-undeduced parameters, we were incorrectly substituting into
    the previously substituted type instead of into its original type.

    In passing this patch also downgrades the "not more specialized"
    diagnostic from a permerror to a pedwarn.

            PR c++/105289
            PR c++/86193

    gcc/cp/ChangeLog:

            * pt.cc (process_partial_specialization): Downgrade "partial
            specialization isn't more specialized" diagnostic from permerror
            to an on-by-default pedwarn.
            (unify) <case TEMPLATE_PARM_INDEX>: When substituting into the
            NTTP type a second time, use the original type not the
            substituted type.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/partial-specialization11.C: New test.
            * g++.dg/template/partial-specialization12.C: New test.