From c61a0092bc236c4be4cb691fcd50ff50e91ab0d6 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Fri, 26 Dec 2014 03:30:51 -0500
Subject: Fix orphan checking (cc #19470). (This is not a complete fix of
 #19470 because of the backwards compatibility feature gate.)

This is a [breaking-change]. The new rules require that, for an impl of a trait defined
in some other crate, two conditions must hold:

1. Some type must be local.
2. Every type parameter must appear "under" some local type.

Here are some examples that are legal:

```rust
struct MyStruct<T> { ... }

// Here `T` appears "under' `MyStruct`.
impl<T> Clone for MyStruct<T> { }

// Here `T` appears "under' `MyStruct` as well. Note that it also appears
// elsewhere.
impl<T> Iterator<T> for MyStruct<T> { }
```

Here is an illegal example:

```rust
// Here `U` does not appear "under" `MyStruct` or any other local type.
// We call `U` "uncovered".
impl<T,U> Iterator<U> for MyStruct<T> { }
```

There are a couple of ways to rewrite this last example so that it is
legal:

1. In some cases, the uncovered type parameter (here, `U`) should be converted
   into an associated type. This is however a non-local change that requires access
   to the original trait. Also, associated types are not fully baked.
2. Add `U` as a type parameter of `MyStruct`:
   ```rust
   struct MyStruct<T,U> { ... }
   impl<T,U> Iterator<U> for MyStruct<T,U> { }
   ```
3. Create a newtype wrapper for `U`
   ```rust
   impl<T,U> Iterator<Wrapper<U>> for MyStruct<T,U> { }
   ```

Because associated types are not fully baked, which in the case of the
`Hash` trait makes adhering to this rule impossible, you can
temporarily disable this rule in your crate by using
`#![feature(old_orphan_check)]`. Note that the `old_orphan_check`
feature will be removed before 1.0 is released.
---
 src/liballoc/lib.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/liballoc/lib.rs')

diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 61b5d43d1cb..d17a54ce6e5 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -64,7 +64,8 @@
        html_root_url = "http://doc.rust-lang.org/nightly/")]
 
 #![no_std]
-#![feature(lang_items, phase, unsafe_destructor, default_type_params)]
+#![allow(unknown_features)]
+#![feature(lang_items, phase, unsafe_destructor, default_type_params, old_orphan_check)]
 
 #[phase(plugin, link)]
 extern crate core;
-- 
cgit 1.4.1-3-g733a5