rust/src/test/ui/borrowck/immutable-arg.rs

// Copyright 2018 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.

//compile-flags: -Z emit-end-regions -Z borrowck=compare

fn foo(_x: u32) {
    _x = 4;
    //~^ ERROR cannot assign to immutable argument `_x` (Mir)
    //~^^ ERROR cannot assign twice to immutable variable `_x` (Ast)
}

fn main() {}