error[E0186]: method `foo` has a `&self` declaration in the trait, but not in the impl
  --> $DIR/E0186.rs:8:5
   |
LL |     fn foo(&self); //~ `&self` used in trait
   |     -------------- `&self` used in trait
...
LL |     fn foo() {} //~ ERROR E0186
   |     ^^^^^^^^ expected `&self` in impl

error: aborting due to previous error

For more information about this error, try `rustc --explain E0186`.