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 error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0596`.