error: type alias `Unused` is never used
  --> $DIR/impl-trait.rs:12:6
   |
LL | type Unused = ();
   |      ^^^^^^
   |
note: the lint level is defined here
  --> $DIR/impl-trait.rs:1:9
   |
LL | #![deny(dead_code)]
   |         ^^^^^^^^^

error: aborting due to 1 previous error