error[E0038]: the trait `A` cannot be made into an object
  --> $DIR/wf-object-safe.rs:19:13
   |
LL |     let _x: &A; //~ ERROR E0038
   |             ^^ the trait `A` cannot be made into an object
   |
   = note: method `foo` references the `Self` type in its arguments or return type

error: aborting due to previous error

For more information about this error, try `rustc --explain E0038`.