error: struct `Unused` is never constructed
  --> $DIR/unused-adt-impls-trait.rs:4:8
   |
LL | struct Unused;
   |        ^^^^^^
   |
note: the lint level is defined here
  --> $DIR/unused-adt-impls-trait.rs:1:9
   |
LL | #![deny(dead_code)]
   |         ^^^^^^^^^

error: aborting due to 1 previous error