error[E0597]: `b` does not live long enough
  --> $DIR/ref-escapes-but-not-over-yield.rs:24:14
   |
24 |         a = &b;
   |              ^ borrowed value does not live long enough
25 |         //~^ ERROR `b` does not live long enough
26 |     };
   |     - `b` dropped here while still borrowed
27 | }
   | - borrowed value needs to live until here

error: aborting due to previous error