error[E0596]: cannot borrow `key` as mutable, as it is not declared as mutable
  --> $DIR/issue-34337.rs:6:9
   |
LL |     get(&mut key);
   |         ^^^^^^^^ cannot borrow as mutable
   |
help: try removing `&mut` here
   |
LL -     get(&mut key);
LL +     get(key);
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0596`.