error: unreachable statement
  --> tests/ui/unreachable.rs:16:9
   |
15 |         let _y = unimplemented!();
   |                  ---------------- any code following this expression is unreachable
16 |         let _z = _y;
   |         ^^^^^^^^^^^^ unreachable statement
   |
note: the lint level is defined here
  --> tests/ui/unreachable.rs:1:9
   |
1  | #![deny(warnings)]
   |         ^^^^^^^^
   = note: `#[deny(unreachable_code)]` implied by `#[deny(warnings)]`