Async fn fundamentals

This initiative is part of the overall async vision roadmap.

Impact

Able to write async fn in traits and trait impls
- Able to easily declare that T: Trait + Send where "every async fn in Trait returns a Send future"
- Traits that use async fn can still be dyn safe though some tuning may be required
- Async functions in traits desugar to impl Trait in traits
Able to write "async fn drop" to declare that the destructor may await
Support for async closures

Milestones

Milestone	State	Key participants
Author evaluation doc for static async trait	done 🎉	tmandry
Author evaluation doc for dyn async trait	done 🎉	tmandry
Author evaluation doc for async drop	💤
Author evaluation doc for impl Trait in traits	done	tmandry
Stabilize type alias impl trait	in-progress	oli-obk
Stabilize generic associated types	done 🎉	jackh726
Author RFC for async fn in traits	done 🎉
Author evaluation doc for async closures	blog posts authored, doc pending	nikomatsakis
Author RFC for impl trait in traits	done
Feature complete for async fn in traits	done 🎉	compiler-errors
Feature complete for impl Trait in traits	done 🎉	compiler-errors
Feature complete for async drop	💤
Feature complete for async closures	💤
Stabilize async fn in traits	proposed	compiler-errors
Stabilize impl trait in traits	proposed	compiler-errors
Stabilize async drop	💤
Stabilize async closures	💤

Design discussions

This directory hosts notes on important design discussions along with their resolutions. In the table of contents, you will find the overall status:

✅ -- Settled! Input only needed if you have identified a fresh consideration that is not covered by the write-up.
💬 -- Under active discussion. Check the write-up, which may contain a list of questions or places where feedback is desired.
💤 -- Paused. Not under active discussion, but we may be updating the write-up from time to time with details.