error: used binding `_foo` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
  --> $DIR/used_underscore_binding.rs:17:5
   |
17 |     _foo + 1
   |     ^^^^
   |
note: lint level defined here
  --> $DIR/used_underscore_binding.rs:6:9
   |
6  | #![deny(used_underscore_binding)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^

error: used binding `_foo` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
  --> $DIR/used_underscore_binding.rs:22:20
   |
22 |     println!("{}", _foo);
   |                    ^^^^

error: used binding `_foo` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
  --> $DIR/used_underscore_binding.rs:24:16
   |
24 |     assert_eq!(_foo, _foo);
   |                ^^^^

error: used binding `_foo` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
  --> $DIR/used_underscore_binding.rs:24:22
   |
24 |     assert_eq!(_foo, _foo);
   |                      ^^^^

error: used binding `_underscore_field` which is prefixed with an underscore. A leading underscore signals that a binding will not be used.
  --> $DIR/used_underscore_binding.rs:39:5
   |
39 |     s._underscore_field += 1;
   |     ^^^^^^^^^^^^^^^^^^^

error: aborting due to 5 previous errors