warning: extern crate `bar` is unused in crate `warn_attr`
  --> $DIR/warn-attr.rs:7:1
   |
LL | #![warn(unused_crate_dependencies)]
   | ^
   |
   = help: remove the dependency or add `use bar as _;` to the crate root
note: the lint level is defined here
  --> $DIR/warn-attr.rs:7:9
   |
LL | #![warn(unused_crate_dependencies)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: 1 warning emitted