rust/src/test/compile-fail/issue-33819.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() {
    let mut op = Some(2);
    match op {
        Some(ref v) => { let a = &mut v; },
        //~^ ERROR:cannot borrow immutable
        //~| use `ref mut v` here to make mutable
        None => {},
    }
}