error[E0597]: `b` does not live long enough
  --> $DIR/ref-escapes-but-not-over-yield.rs:25:5
   |
24 |         a = &b; //~ ERROR
   |              - borrow occurs here
25 |     };
   |     ^ `b` dropped here while still borrowed
26 | }
   | - borrowed value needs to live until here

error: aborting due to previous error