https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90490
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- And we also started rejecting this: struct R { constexpr operator bool() { return false;} }; template <typename> struct S { void g() noexcept(decltype(R{ }) { }) { } };