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Update E0210 to match RFC 2451

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This commit is contained in:
Ohad Ravid 2019-11-08 21:40:30 +01:00
parent eb981a1da4
commit 7e94cc37e8
1 changed files with 16 additions and 6 deletions
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22
src/librustc_typeck/error_codes.rs
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@ -2058,8 +2058,13 @@ E0210: r##"
This error indicates a violation of one of Rust's orphan rules for trait
implementations. The rule concerns the use of type parameters in an
implementation of a foreign trait (a trait defined in another crate), and
states that type parameters must be "covered" by a local type. To understand
what this means, it is perhaps easiest to consider a few examples.
states that type parameters must be "covered" by a local type.
When implementing a foreign trait for a foreign type,
the trait must have one or more type parameters.
A type local to your crate must appear before any use of any type parameters.
To understand what this means, it is perhaps easier to consider a few examples.
If `ForeignTrait` is a trait defined in some external crate `foo`, then the
following trait `impl` is an error:
@ -2117,12 +2122,17 @@ impl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }
where `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`
are types. One of the types `T0, ..., Tn` must be a local type (this is another
orphan rule, see the explanation for E0117). Let `i` be the smallest integer
such that `Ti` is a local type. Then no type parameter can appear in any of the
`Tj` for `j < i`.
orphan rule, see the explanation for E0117).
For information on the design of the orphan rules, see [RFC 1023].
Both of the folowing must be true:
1. At least one of the types T0..=Tn must be a local type.
Let Ti be the first such type.
2. No uncovered type parameters P1..=Pm may appear in T0..Ti (excluding Ti).
For information on the design of the orphan rules,
see [RFC 2451] and [RFC 1023].
[RFC 2451]: https://rust-lang.github.io/rfcs/2451-re-rebalancing-coherence.html
[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md
"##,