https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92067
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- We need to be careful about this in SFINAE contexts. It can't be a hard error, because it's extremely common for constructors to be constrained with std::is_constructible, and for overload resolution to consider constructors for incomplete types.
