208dd2032b
Add support for `for await` loops This adds support for `for await` loops. This includes parsing, desugaring in AST->HIR lowering, and adding some support functions to the library. Given a loop like: ```rust for await i in iter { ... } ``` this is desugared to something like: ```rust let mut iter = iter.into_async_iter(); while let Some(i) = loop { match core::pin::Pin::new(&mut iter).poll_next(cx) { Poll::Ready(i) => break i, Poll::Pending => yield, } } { ... } ``` This PR also adds a basic `IntoAsyncIterator` trait. This is partly for symmetry with the way `Iterator` and `IntoIterator` work. The other reason is that for async iterators it's helpful to have a place apart from the data structure being iterated over to store state. `IntoAsyncIterator` gives us a good place to do this. I've gated this feature behind `async_for_loop` and opened #118898 as the feature tracking issue. r? `@compiler-errors` |
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messages.ftl |