https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- Diagnostics for narrowing conversions involving non-constants are controlled by -Wnarrowing (allowing them to be either warnings or errors). But narrowing conversions involving constants are always errors. Case labels must be constants, so making this depend on -Wnarrowing wouldn't seem appropriate to me.
