Async, await and @autoclosure

[xwu (Xiaodi Wu)]

@George

/// Error: call is 'async' in an autoclosure argument that is not marked with 'await'
let _ = await foo() | bar()

Seems like a bug.

@George

There is some discussion of async , await , and @autoclosure here , but it doesn't mention operators and it isn't 100% clear on the how the compiler would interpret await computeArgumentLater(await getIntSlowly()) (my reading of this is that there would be a suspension point both prior to and in the body of computeArgumentLater ).

Overall, I think the right move is to only apply autoclosure semantics when an argument is not labeled await .

The point of the discussion in the proposal is that only one await is ever required per statement, just like only one try is ever required per statement, and how autoclosures must work in order to observe that principle.