warning: unused extern crate
  --> $DIR/no-macro-use-attr.rs:16:1
   |
LL | extern crate derive_a;
   | ^^^^^^^^^^^^^^^^^^^^^^ help: remove it
   |
note: lint level defined here
  --> $DIR/no-macro-use-attr.rs:14:9
   |
LL | #![warn(unused_extern_crates)]
   |         ^^^^^^^^^^^^^^^^^^^^

error: compilation successful
  --> $DIR/no-macro-use-attr.rs:20:1
   |
LL | fn main() {} //~ ERROR compilation successful
   | ^^^^^^^^^^^^

error: aborting due to previous error