error[E0596]: cannot borrow `data` as mutable, as it is not declared as mutable --> $DIR/issue-61187.rs:6:5 | LL | data.reverse(); | ^^^^ cannot borrow as mutable | help: consider changing this to be mutable | LL | async fn response(mut data: Vec) { | +++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0596`.