3379721a30
Elaborate `Future::Output` when printing opaque `impl Future` type I would love to see the `Output =` type when printing type errors involving opaque `impl Future`. [Test code](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=a800b481edd31575fbcaf5771a9c3678) Before (cut relevant part of output): ``` note: while checking the return type of the `async fn` --> /home/michael/test.rs:5:19 | 5 | async fn bar() -> usize { | ^^^^^ checked the `Output` of this `async fn`, found opaque type = note: expected type `usize` found opaque type `impl Future` ``` After: ``` note: while checking the return type of the `async fn` --> /home/michael/test.rs:5:19 | 5 | async fn bar() -> usize { | ^^^^^ checked the `Output` of this `async fn`, found opaque type = note: expected type `usize` found opaque type `impl Future<Output = usize>` ``` Note the "found opaque type `impl Future<Output = usize>`" in the new output. ---- Questions: 1. We skip printing the output type when it's a projection, since I have been seeing some types like `impl Future<Output = <[static generator@/home/michael/test.rs:2:11: 2:21] as Generator<ResumeTy>>::Return>` which are not particularly helpful and leak implementation detail. * Am I able to normalize this type within `rustc_middle::ty::print::pretty`? Alternatively, can we normalize it when creating the diagnostic? Otherwise, I'm fine with skipping it and falling back to the old output. * Should I suppress any other types? I didn't encounter anything other than this generator projection type. 2. Not sure what the formatting of this should be. Do I include spaces in `Output = `? |
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