[Bug c++/114393] [14 regression] over eager "invalid use of void expression" ?

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114393

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-03-19
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
r14-2170 started to reject it

Author: Patrick Palka
Date:   Wed Jun 28 20:43:33 2023

    c++: ahead of time variable template-id coercion [PR89442]

    This patch makes us coerce the arguments of a variable template-id ahead
    of time, as we do for class template-ids, which causes us to immediately
    diagnose template parm/arg kind mismatches and arity mismatches.

    Unfortunately this causes a regression in cpp1z/constexpr-if20.C: coercing
    the variable template-id m<ar, as> ahead of time means we strip it of
    typedefs, yielding m<typename C<i>::q, typename C<j>::q>, but in this
    stripped form we're directly using 'i' and so we expect to have captured
    it.  This is a variable template version of PR107437.

            PR c++/89442
            PR c++/107437

    gcc/cp/ChangeLog:

            * cp-tree.h (lookup_template_variable): Add complain parameter.
            * parser.cc (cp_parser_template_id): Pass tf_warning_or_error
            to lookup_template_variable.
            * pt.cc (lookup_template_variable): Add complain parameter.
            Coerce template arguments here ...
            (finish_template_variable): ... instead of here.
            (lookup_and_finish_template_variable): Check for error_mark_node
            result from lookup_template_variable.
            (tsubst_copy) <case TEMPLATE_ID_EXPR>: Pass complain to
            lookup_template_variable.
            (instantiate_template): Use build2 instead of
            lookup_template_variable to build a TEMPLATE_ID_EXPR
            for most_specialized_partial_spec.