From b5b2a8984e57260bb91d3327490da74f6fa310db Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Thu, 14 Nov 2019 13:08:23 +0100 Subject: [PATCH] Move E0210 to new error location --- src/librustc_error_codes/error_codes/E0210.md | 23 +++++++++++++++---- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/src/librustc_error_codes/error_codes/E0210.md b/src/librustc_error_codes/error_codes/E0210.md index f8ddaecc831..dc2fd9b0ca0 100644 --- a/src/librustc_error_codes/error_codes/E0210.md +++ b/src/librustc_error_codes/error_codes/E0210.md @@ -1,8 +1,13 @@ 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: @@ -60,10 +65,18 @@ impl ForeignTrait 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). + +Both of the following 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]. For information on the design of the orphan rules, see [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 -- 2.44.0