error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable --> $DIR/issue-93078.rs:11:9 | LL | self.modify(); | ^^^^ cannot borrow as mutable | = note: as `Self` may be unsized, this call attempts to take `&mut &mut self` = note: however, `&mut self` expands to `self: &mut Self`, therefore `self` cannot be borrowed mutably error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.