warning: extern crate `bar` is unused in crate `warn_cmdline`
  --> $DIR/warn-cmdline.rs:8:1
   |
LL | fn main() {}
   | ^
   |
   = help: remove the dependency or add `use bar as _;` to the crate root
   = note: requested on the command line with `-W unused-crate-dependencies`

warning: 1 warning emitted