error: enum is never used: `E`
  --> $DIR/empty-unused-enum.rs:3:6
   |
LL | enum E {}
   |      ^
   |
note: the lint level is defined here
  --> $DIR/empty-unused-enum.rs:1:9
   |
LL | #![deny(unused)]
   |         ^^^^^^
   = note: `#[deny(dead_code)]` implied by `#[deny(unused)]`

error: aborting due to previous error