Semantics of control flow operators (return, continue, ?) in async blocks is severely underdocumented

[matklad]

As a novice Rust programmer, I was quite surprised that the following works:

#[tokio::main]
async fn main() {
    let f = async { return 92 };
    assert_eq!(f.await, 92);
}

I don't remeber reading that in any kind of docs, and looking at the

• async book https://rust-lang.github.io/async-book/01_getting_started/04_async_await_primer.html
• async keyword https://doc.rust-lang.org/stable/std/keyword.async.html
• return keyword https://doc.rust-lang.org/stable/std/keyword.return.html

didn't show up any example of the syntax.

This is documented in the reference (rust-lang/reference#1262), but without an example.