warning: unknown lint: `not_a_real_lint`
  --> $DIR/lint-unknown-lint.rs:11:10
   |
LL | #![allow(not_a_real_lint)] //~ WARN unknown lint
   |          ^^^^^^^^^^^^^^^
   |
   = note: #[warn(unknown_lints)] on by default

error: unused variable: `unused`
  --> $DIR/lint-unknown-lint.rs:13:17
   |
LL | fn main() { let unused = (); } //~ ERROR unused variable
   |                 ^^^^^^ help: consider using `_unused` instead
   |
note: lint level defined here
  --> $DIR/lint-unknown-lint.rs:12:9
   |
LL | #![deny(unused)]
   |         ^^^^^^
   = note: #[deny(unused_variables)] implied by #[deny(unused)]

error: aborting due to previous error