https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99992
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- C++11 says: "its function-body shall be = delete, = default, or a compound-statement that contains only — null statements, — static_assert-declarations — typedef declarations and alias-declarations that do not define classes or enumerations, — using-declarations, — using-directives, — and exactly one return statement;" so perhaps if we on a constexpr function template see anything other than the above ones, even if it e.g. could be some statement that is using some parameter pack that would for empty pack instantiate to nothing, we could diagnose it?
