https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109277
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I know cppreference is not the standard but usually it has a good summary. From: https://en.cppreference.com/w/cpp/types/is_convertible : ``` >From and To shall each be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined. ``` So someone who understands the C++ standard better than me should be able to answer if this is in fact illformed code.
