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Suggest Trait<Ty: Trait2> syntax when user typed Trait<Ty = Trait2> #105056
Description
Consider the following code:
trait Foo {}
fn bar(_: impl Iterator<Item = Foo>) {}
// Or another similar case:
trait Bar {
type X: Iterator<Item = Foo>;
}The current output is:
error[E0782]: trait objects must include the `dyn` keyword
--> src/lib.rs:3:32
|
3 | fn bar(_: impl Iterator<Item = Foo>) {}
| ^^^
|
help: add `dyn` keyword before this trait
|
3 | fn bar(_: impl Iterator<Item = dyn Foo>) {}
| +++
This is reasonable especially in light of the ongoing migration from the old dyn-less trait object syntax. However, an alternative interpretation of the syntax error is that the user accidentally used a type equality bound = when they actually meant a trait bound :. The error message could include a suggestion to replace = with :.
help: or if you meant to write a trait bound, replace `=` with `:`
|
3 | fn bar(_: impl Iterator<Item = Foo>) {}
| --
3 | fn bar(_: impl Iterator<Item: Foo>) {}
| +
See also related #99304 which proposes that impl Foo should be suggested rather than dyn Foo.
Reacted by Trevor Gross
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Area: Messages for errors, warnings, and lintsArea: Suggestions generated by the compiler applied by `cargo fix``#![feature(associated_type_bounds)]`Relevant to the compiler team, which will review and decide on the PR/issue.This issue requires a nightly compiler in some way. When possible, use a F-* label instead.
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fmease commentedon Nov 29, 2022
This should only be suggested on nightly as associated type bounds are still unstable.
jdahlstrom commentedon Nov 29, 2022
@fmease Oops, good point. Not sure how I thought that compiled on stable, mea culpa. I guess the compiler could suggest using the stable
where X: Trait, X::Ty: Trait2syntax if the user attempts to use ATBs, but that should probably be its own issue.Rollup merge of rust-lang#122120 - fmease:sugg-assoc-ty-bound-on-eq-b…
Unrolled build for rust-lang#122120