error[E0382]: use of moved value: `a`
  --> $DIR/option_mut.rs:6:20
   |
LL |     let a = Some(&mut ());
   |         - move occurs because `a` has type `Option<&mut ()>`, which does not implement the `Copy` trait
LL |     let _ = method(a);
   |                    - value moved here
LL |     let _ = method(a);
   |                    ^ value used here after move
   |
note: consider changing this parameter type in function `method` to borrow instead if owning the value isn't necessary
  --> $DIR/option_mut.rs:1:14
   |
LL | fn method(a: Option<&mut ()>) {}
   |    ------    ^^^^^^^^^^^^^^^ this parameter takes ownership of the value
   |    |
   |    in this function

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0382`.