Implement new coherence orphan rules #20416
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Looks like you accidentally added a binary: src/test/run-pass/coherence-covered-type-parameter |
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r=me once the stray binary is removed (which prevents passing |
… of rust-lang#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.
rules and cannot be updated until the libraries are synced, nor can they opt in to the old semantics.
various bugs in `trait_id_of_impl`. The end result was that looking up the "trait_id_of_impl" with a trait's def-id yielded the same trait again, even though it ought to have yielded None.
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Conflicts: src/test/run-pass/issue-15734.rs src/test/run-pass/issue-3743.rs
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For the moment, a feature gate is provided to opt out, since many of the traits require what will be illegal patterns, since associated types are not fully working yet.
r? @aturon
cc @arielb1
cc #19470