warning: type alias `Z` is never used
  --> $DIR/issue-37515.rs:5:6
   |
LL | type Z = dyn for<'x> Send;
   |      ^
   |
note: the lint level is defined here
  --> $DIR/issue-37515.rs:3:9
   |
LL | #![warn(unused)]
   |         ^^^^^^
   = note: `#[warn(dead_code)]` implied by `#[warn(unused)]`

warning: 1 warning emitted