https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84684
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Or also defining another method in union_composition, like:
static constexpr auto make_value_to_char1()
{
constexpr auto N = sizeof...(alphabet_types);
return N;
}
makes it go away.
