error: The function/method `takes_an_immutable_reference` doesn't need a mutable reference
  --> $DIR/mut_reference.rs:22:34
   |
22 |     takes_an_immutable_reference(&mut 42);
   |                                  ^^^^^^^
   |
   = note: `-D unnecessary-mut-passed` implied by `-D warnings`

error: The function/method `as_ptr` doesn't need a mutable reference
  --> $DIR/mut_reference.rs:24:12
   |
24 |     as_ptr(&mut 42);
   |            ^^^^^^^

error: The function/method `takes_an_immutable_reference` doesn't need a mutable reference
  --> $DIR/mut_reference.rs:28:44
   |
28 |     my_struct.takes_an_immutable_reference(&mut 42);
   |                                            ^^^^^^^