error[E0004]: non-exhaustive patterns: `(None, None)` and `(Some(_), Some(_))` not covered
  --> $DIR/issue-2111.rs:2:11
   |
LL |     match (a, b) {
   |           ^^^^^^ patterns `(None, None)` and `(Some(_), Some(_))` not covered
   |
   = note: the matched value is of type `(Option<usize>, Option<usize>)`
   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms

error: aborting due to previous error

For more information about this error, try `rustc --explain E0004`.