error: enum `Foo` is never used
  --> $DIR/unused-adt-impls-pub-trait.rs:3:6
   |
LL | enum Foo {}
   |      ^^^
   |
note: the lint level is defined here
  --> $DIR/unused-adt-impls-pub-trait.rs:1:9
   |
LL | #![deny(dead_code)]
   |         ^^^^^^^^^

error: aborting due to 1 previous error