Proposal: shall we use async_fn_in_traits?

[PureWhiteWu]

Now that async_fn_in_traits has reached MVP in nightly, and will hopefully be stabilized in six months.

Shall we use that?

FYI:

1. https://blog.rust-lang.org/inside-rust/2022/11/17/async-fn-in-trait-nightly.html
2. Tracking Issue for async_fn_in_trait, return_position_impl_trait_in_trait rust-lang/rust#91611

[PureWhiteWu]

I've tried this, but seems we have encountered the Send bound problem in volo.

I will try again some time later when this feature is more mature.

[my-vegetable-has-exploded]

After using async_fn_in_traits, will we be able to provide msrv?

[PureWhiteWu]

@my-vegetable-has-exploded Yes, this will be a breaking change, we are discussing and testing the new design.
Long story short, we are going to change Service to something like this:

pub trait Service<Cx, Request> {
 /// Responses given by the service.
 type Response;
 /// Errors produced by the service.
 type Error;
 /// Process the request and return the response asynchronously.
 fn call<'cx, 's>(&'s self, cx: &'cx mut Cx, req: Request) -> impl Future<Output = Result<Self::Response, Self::Error>> + Send + 'cx
 where
 's: 'cx;
}

But we are not quite sure if this works fine, so we need some more tests.

[PureWhiteWu]

We met this issue rust-lang/rust#100013 when migrating to rpitit, maybe we need to wait for this bug to be fixed.