pub(crate) unsafe auto trait UnsafeUnpin { }
Used to determine whether a type contains any UnsafePinned (or PhantomPinned) internally, but not through an indirection. This affects, for example, whether we emit noalias metadata for &mut T or not.
UnsafePinned
PhantomPinned
noalias
&mut T
This is part of RFC 3467, and is tracked by #125735.