[Bug c++/99631] decltype of non-type template-parameter shouldn't be const

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:b9e02590f7d35f1f8e8e95ab1f2e30f24113f551

commit r13-7835-gb9e02590f7d35f1f8e8e95ab1f2e30f24113f551
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Sep 19 08:21:05 2023 -0400

    c++: constness of decltype of NTTP object [PR99631]

    This corrects resolving decltype of a (class) NTTP object as per
    [dcl.type.decltype]/1.2 and [temp.param]/6 in the type-dependent case.

    Note that in the non-dependent case we resolve the decltype ahead of
    time, in which case finish_decltype_type drops the const VIEW_CONVERT_EXPR
    wrapper around the TEMPLATE_PARM_INDEX, and the latter has the desired
    non-const type.

    In the type-dependent case, at instantiation time tsubst drops the
    VIEW_CONVERT_EXPR since the substituted NTTP is the already-const object
    created by get_template_parm_object.  So in this case finish_decltype_type
    sees the const object, which this patch now adds special handling for.

            PR c++/99631

    gcc/cp/ChangeLog:

            * semantics.cc (finish_decltype_type): For an NTTP object,
            return its type modulo cv-quals.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/nontype-class60.C: New test.

    (cherry picked from commit ddd064e3571c4a9e6258c75eba65585a07367712)