rust/src/test/compile-fail/E0302.rs

// Copyright 2016 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 main() {
    match Some(()) {
        None => { },
        option if { option = None; false } => { }, //~ ERROR E0302
        //~| NOTE assignment in pattern guard
        Some(_) => { }
    }
}