warning: type alias is never used: `Z`
  --> $DIR/issue-37515.rs:5:1
   |
LL | type Z = dyn for<'x> Send;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> $DIR/issue-37515.rs:3:9
   |
LL | #![warn(unused)]
   |         ^^^^^^
   = note: `#[warn(dead_code)]` implied by `#[warn(unused)]`