| // 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. |
| |
| // This test is for #29859, we need to ensure auto traits, |
| // (also known previously as default traits), do not have |
| // supertraits. Since the compiler synthesizes these |
| // instances on demand, we are essentially enabling |
| // users to write axioms if we view trait selection, |
| // as a proof system. |
| // |
| // For example the below test allows us to add the rule: |
| // forall (T : Type), T : Copy |
| // |
| // Providing a copy instance for *any* type, which |
| // is most definitely unsound. Imagine copying a |
| // type that contains a mutable reference, enabling |
| // mutable aliasing. |
| // |
| // You can imagine an even more dangerous test, |
| // which currently compiles on nightly. |
| // |
| // fn main() { |
| // let mut i = 10; |
| // let (a, b) = copy(&mut i); |
| // println!("{:?} {:?}", a, b); |
| // } |
| |
| #![feature(optin_builtin_traits)] |
| |
| auto trait Magic: Copy {} //~ ERROR E0568 |
| impl<T:Magic> Magic for T {} |
| |
| fn copy<T: Magic>(x: T) -> (T, T) { (x, x) } |
| |
| #[derive(Debug)] |
| struct NoClone; |
| |
| fn main() { |
| let (a, b) = copy(NoClone); |
| println!("{:?} {:?}", a, b); |
| } |
