error[E0626]: borrow may still be in use when `gen` block yields
  --> $DIR/self_referential_gen_block.rs:9:21
   |
LL |         let mut x = gen {
   |                     --- within this `gen` block
LL |             let y = 42;
LL |             let z = &y;
   |                     ^^
LL |             yield 43;
   |             -------- possible yield occurs here

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0626`.