error[E0596]: cannot borrow `arg` as mutable, as it is not declared as mutable --> $DIR/mut-suggestion.rs:12:5 | LL | arg.mutate(); | ^^^ cannot borrow as mutable | help: consider changing this to be mutable | LL | fn func(mut arg: S) { | +++ error[E0596]: cannot borrow `local` as mutable, as it is not declared as mutable --> $DIR/mut-suggestion.rs:20:5 | LL | local.mutate(); | ^^^^^ cannot borrow as mutable | help: consider changing this to be mutable | LL | let mut local = S; | +++ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0596`.