rust/src/test/compile-fail/issue-15094.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.

#![feature(unboxed_closures)]

use std::{fmt, ops};

struct Debuger<T> {
    x: T
}

impl<T: fmt::Debug> ops::FnOnce<(),> for Debuger<T> {
    type Output = ();
    fn call_once(self, _args: ()) {
    //~^ ERROR `call_once` has an incompatible type for trait
    //~| expected "rust-call" fn,
    //~| found "Rust" fn
        println!("{:?}", self.x);
    }
}

fn make_shower<T>(x: T) -> Debuger<T> {
    Debuger { x: x }
}

pub fn main() {
    let show3 = make_shower(3);
    show3();
}