[Bug c++/115378] [14/15 Regression] ICE with lambda function as a default template argument with variadic templates in some cases

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115378

--- Comment #7 from GCC 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:5c761395402a730535983a5e49ef1775561ebc61

commit r15-1103-g5c761395402a730535983a5e49ef1775561ebc61
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 7 12:12:30 2024 -0400

    c++: lambda in pack expansion [PR115378]

    Here find_parameter_packs_r is incorrectly treating the 'auto' return
    type of a lambda as a parameter pack due to Concepts-TS specific logic
    added in r6-4517, leading to confusion later when expanding the pattern.

    Since we intend on removing Concepts TS support soon anyway, this patch
    fixes this by restricting the problematic logic with flag_concepts_ts.
    Doing so revealed that add_capture was relying on this logic to set
    TEMPLATE_TYPE_PARAMETER_PACK for the 'auto' type of an pack expansion
    init-capture, which we now need to do explicitly.

            PR c++/115378

    gcc/cp/ChangeLog:

            * lambda.cc (lambda_capture_field_type): Set
            TEMPLATE_TYPE_PARAMETER_PACK on the auto type of an init-capture
            pack expansion.
            * pt.cc (find_parameter_packs_r) <case TEMPLATE_TYPE_PARM>:
            Restrict TEMPLATE_TYPE_PARAMETER_PACK promotion with
            flag_concepts_ts.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/decltype-auto-103497.C: Adjust expected diagnostic.
            * g++.dg/template/pr95672.C: Likewise.
            * g++.dg/cpp2a/lambda-targ5.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>