Macro completion::completion_async

macro_rules! completion_async {
    ($($tt:tt)*) => { ... };
}

This is supported on crate features macro and std only.

A bang macro to generate completion async blocks.

These async blocks evaluate to a CompletionFuture, and you can .await other CompletionFutures inside of them.

Soundness

There is currently a slight soundness issue inside these async blocks: if you invoke an attribute macro inside the async block on some code that awaits a completion future, and that attribute macro moves the code to a regular, non-completion async block, you are able to create a Future that unsoundly wraps a CompletionFuture. Or in code, this:

completion_async! {
    #[some_macro]
    completion_future.await;
}

Could expand to:

completion_async! {
    async {
        // Oh no! We have awaited a completion future inside a regular async block.
        completion_future.await;
    }
}

This macro does not require unsafe because I decided that this unsoundness is so particular that it is highly unlikely it will actually occur in user code. If you know of a fix for this, it would be highly appreciated.

Examples

use completion::{FutureExt, completion_async, future};

let fut = completion_async! {
    let fut = async { 3 };
    let completion_fut = async { 5 }.into_completion();
    fut.await + completion_fut.await
};
assert_eq!(future::block_on(fut), 8);