error[E0185]: method `foo` has a `&self` declaration in the impl, but not in the trait
  --> $DIR/E0185.rs:9:5
   |
LL |     fn foo();
   |     --------- trait method declared without `&self`
...
LL |     fn foo(&self) {}
   |     ^^^^^^^^^^^^^ `&self` used in impl

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0185`.