error[E0596]: cannot borrow `f` as mutable, as it is not declared as mutable --> $DIR/issue-84044-drop-non-mut.rs:5:10 | LL | drop(&mut f); | ^^^^^^ cannot borrow as mutable | help: consider changing this to be mutable | LL | let mut f = || {}; | +++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0596`.