[Bug c++/112594] Non-type template parameter created with converting constructor sometimes has original type

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112594

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:f1e5bf0d83ee4da81b6317c6d7f1278fe7eaa5a0

commit r14-8291-gf1e5bf0d83ee4da81b6317c6d7f1278fe7eaa5a0
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jan 17 17:29:33 2024 -0500

    c++: alias template argument conversion [PR112632]

    We've had a problem with lost conversions to template parameter types for a
    while now; looking at this PR, it occurred to me that the problem is really
    with alias (and concept) templates, since we do substitution of dependent
    arguments into them in a way that we don't for other templates.  And fixing
    that specific problem is a lot simpler than adding IMPLICIT_CONV_EXPR
around
    all dependent template arguments the way I gave up on for 111357.

    The other part of the fix was changing tsubst_expr to actually call
    convert_nontype_argument instead of assuming it will eventually happen.

    I waffled about stripping the forced conversion when !force_conv
    vs. skipping them in iterative_hash_template_arg and
    template_args_equal (like we already do for some other conversions) and
    decided to go with the former, but that isn't a strong preference if it
    turns out to be somehow problematic.

            PR c++/112632
            PR c++/112594
            PR c++/111357
            PR c++/104594
            PR c++/67898

    gcc/cp/ChangeLog:

            * cp-tree.h (IMPLICIT_CONV_EXPR_FORCED): New.
            * pt.cc (expand_integer_pack): Remove 111357 workaround.
            (maybe_convert_nontype_argument): Add force parm.
            (convert_template_argument): Handle alias template args
            specially.
            (tsubst_expr): Don't ignore IMPLICIT_CONV_EXPR_NONTYPE_ARG.
            * error.cc (dump_expr) [CASE_CONVERT]: Handle null optype.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/alias-decl-nontype1.C: New test.
            * g++.dg/cpp2a/concepts-narrowing1.C: New test.
            * g++.dg/cpp2a/nontype-class63.C: New test.
            * g++.dg/cpp2a/nontype-class63a.C: New test.