error: opaque type's hidden type cannot be another opaque type from the same scope
  --> $DIR/two_tait_defining_each_other3.rs:10:16
   |
LL |         return x;  // B's hidden type is A (opaquely)
   |                ^ one of the two opaque types used here has to be outside its defining scope
   |
note: opaque type whose hidden type is being assigned
  --> $DIR/two_tait_defining_each_other3.rs:4:10
   |
LL | type B = impl Foo;
   |          ^^^^^^^^
note: opaque type being used as hidden type
  --> $DIR/two_tait_defining_each_other3.rs:3:10
   |
LL | type A = impl Foo;
   |          ^^^^^^^^

error: aborting due to previous error