error: non-binding let on a synchronization lock
  --> $DIR/let_underscore_lock.rs:6:9
   |
LL |     let _ = data.lock().unwrap();
   |         ^   ^^^^^^^^^^^^^^^^^^^^ this binding will immediately drop the value assigned to it
   |         |
   |         this lock is not assigned to a binding and is immediately dropped
   |
   = note: `#[deny(let_underscore_lock)]` on by default
help: consider binding to an unused variable to avoid immediately dropping the value
   |
LL |     let _unused = data.lock().unwrap();
   |         ~~~~~~~
help: consider immediately dropping the value
   |
LL |     drop(data.lock().unwrap());
   |     ~~~~~                    +

error: aborting due to previous error