error[E0408]: variable `y` is not bound in all patterns
  --> $DIR/E0408.rs:5:19
   |
LL |         Some(y) | None => {}
   |              -    ^^^^ pattern doesn't bind `y`
   |              |
   |              variable not in all patterns

error: aborting due to previous error

For more information about this error, try `rustc --explain E0408`.