663fb5a0e9
[doc] `poll_fn`: explain how to `pin` captured state safely Usage of `Pin::new_unchecked(&mut …)` is dangerous with `poll_fn`, even though the `!Unpin`-infectiousness has made things smoother. Nonetheless, there are easy ways to avoid the need for any `unsafe` altogether, be it through `Box::pin`ning, or the `pin!` macro. Since the latter only works within an `async` context, showing an example artificially introducing one ought to help people navigate this subtlety with safety and confidence. ## Preview https://user-images.githubusercontent.com/9920355/230092494-da22fdcb-0b8f-4ff4-a2ac-aa7d9ead077a.mov ```@rustbot``` label +A-docs