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 1 previous error

For more information about this error, try `rustc --explain E0596`.