error: unused extern crate --> $DIR/extern-crate-used.rs:18:1 | LL | extern crate core; | ^^^^^^^^^^^^^^^^^^ help: remove it | note: the lint level is defined here --> $DIR/extern-crate-used.rs:6:9 | LL | #![deny(unused_extern_crates)] | ^^^^^^^^^^^^^^^^^^^^ error: aborting due to 1 previous error