src/test/auxiliary/issue-20727.rs

// Copyright 2015 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.

pub trait Deref {
    type Target: ?Sized;

    fn deref<'a>(&'a self) -> &'a Self::Target;
}

pub trait Add<RHS = Self> {
    type Output;

    fn add(self, rhs: RHS) -> Self::Output;
}


pub trait Bar {}
pub trait Deref2 {
    type Target: Bar;

    fn deref(&self) -> Self::Target;
}

pub trait Index<Idx: ?Sized> {
    type Output: ?Sized;
    fn index(&self, index: Idx) -> &Self::Output;
}

pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
    fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
}