error[E0277]: the trait bound `(): Add<A>` is not satisfied
  --> $DIR/associated-types-ICE-when-projecting-out-of-err.rs:23:11
   |
LL |     r = r + a;
   |           ^ the trait `Add<A>` is not implemented for `()`
   |
help: this trait has no implementations, consider adding one
  --> $DIR/associated-types-ICE-when-projecting-out-of-err.rs:15:1
   |
LL | trait Add<RHS=Self> {
   | ^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.