rust/src/test/compile-fail/method-help-unsatisfied-bound.rs

// Copyright 2014 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.

struct Foo;

fn main() {
    let a: Result<(), Foo> = Ok(());
    a.unwrap();
    //~^ ERROR no method named `unwrap` found for type `std::result::Result<(), Foo>`
    //~| NOTE the following trait bounds were not satisfied: `Foo : std::fmt::Debug`
}