rust/src/test/compile-fail/issue-2111.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

fn foo(a: Option<usize>, b: Option<usize>) {
  match (a,b) {
  //~^ ERROR: non-exhaustive patterns: `(None, None)` not covered
    (Some(a), Some(b)) if a == b => { }
    (Some(_), None) |
    (None, Some(_)) => { }
  }
}

fn main() {
  foo(None, None);
}