https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107492
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- I ... don't remember. It was needed to avoid some error, maybe from std::visit<const void>(vis, var) of something like that. But either we never added a test for it or something changed. I can't reproduce an error without that partial specialization now.
