error[E0408]: variable `y` is not bound in all patterns
  --> $DIR/E0408.rs:15:19
   |
15 |         Some(y) | None => {} //~  ERROR variable `y` is not bound in all patterns
   |              -    ^^^^ pattern doesn't bind `y`
   |              |
   |              variable not in all patterns

error: aborting due to previous error