Remove the old await! macro

[cramertj]

This doesn't work anymore, and its continued presence is cause for confusion. yield can no longer be used to return Pending from an async body.

cc #60660
cc @taiki-e
cc tokio-rs/tokio#1080

[rust-highfive]

r? @nikomatsakis

(rust_highfive has picked a reviewer for you, use r? to override)

[taiki-e]

Hmm... I thought that we could fix this by changing std::r#await! macro as follows and the compiler ignores await! macro (and maybe adjust the feature gate).

macro_rules! r#await {
    ($e:expr) => { 
        $e.await
    }
}

However, if it is difficult, I think this PR is fine.

[nikomatsakis]

I was also assuming that we would change await! to just be foo.await -- at least for now. I guess there is a good question of when to remove support "for good".

[cramertj]

@taiki-e Unfortunately that doesn't work because we ban yield in async bodies, so the yield inside the await! macro won't work.

[cramertj]

@nikomatsakis I think that'd still be confusing since await!(...) doesn't call the std macro anymore.

[taiki-e]

@cramertj

@taiki-e Unfortunately that doesn't work because we ban yield in async bodies, so the yield inside the await! macro won't work.

The current await! macro doesn't work because it uses yield internally. My suggestion is to use the await syntax instead of them. I think it works because it is almost the same as a macro such as futures::pending.

[nikomatsakis]

@cramertj oh, I didn't realize that. Never mind, then.

[cramertj]

@taiki-e yeah, we could do that, but people could also do that in an external library, and as I mentioned to @nikomatsakis, I think it runs the risk of being more confusing than helpful.

[taiki-e]

@taiki-e yeah, we could do that, but people could also do that in an external library, and as I mentioned to @nikomatsakis, I think it runs the risk of being more confusing than helpful.

Oh, that makes sense.

[Centril]

@bors r=nikomatsakis,Centril

[bors]

📌 Commit df41e4f has been approved by nikomatsakis,Centril