[Bug c++/118104] New: [trunk regression] ICE when substituting packs into type aliases

[zyn7109 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118104

            Bug ID: 118104
           Summary: [trunk regression] ICE when substituting packs into
                    type aliases
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zyn7109 at gmail dot com
  Target Milestone: ---

GCC trunk currently ICEs for the following code

template <class... Ts> struct X {
  template <class... Us> using Y = X<void(Ts, Us)...>;
};

template <class A, class... P>
using any_pairs_list_4 = X<int, int>::Y<A, P...>;

int main() {
  any_pairs_list_4<int, int> array;
}

This seems to be a trunk regression because GCC 14 works fine (see godbolt link
https://godbolt.org/z/r6c7TcvcW)