HTTP/2 Upgraded wrongly uses a transparent uninhabited type #3966
Description
As noted in rust-lang/rust#147588, the H2Upgraded type in hyper wrongly uses a repr(transparent) value on a stuct containing enum Neutered {}. It seems that this was making use of behavior of the current compiler that isn't specified, and would like to be changed.
That code should be refactored to no longer need such a repr(transparent) transmute.