https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87404
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> --- It comes from Clang, where there's no documentation, only a warning message: -Wenum-compare: comparison of two values with different enumeration types -Wenum-compare-switch: comparison of two values with different enumeration types in switch statement
