Tracking issue for `#![feature(async_closure)]` (RFC 2394 / RFC 3668)

[Centril]

This is a tracking issue for #![feature(async_closure)] (rust-lang/rfcs#2394).
The feature gate provides the async |...| expr closure syntax.

As with all tracking issues for the language, please file anything unrelated to implementation history, that is: bugs and design questions, as separate issues as opposed to leaving comments here. The status of the feature should also be covered by the feature gate label. Please do not ask about developments here.

Steps:

• Implement the RFC
• Accept another RFC
  • Async closures rfcs#3668
• Implement it: Rework support for async closures; allow them to return futures that borrow from the closure's captures #120361
• Adjust documentation (see instructions on rustc-guide)
• Stabilization PR (see instructions on rustc-guide)
  • Stabilize async closures (RFC 3668) #132706

Open questions (RFC 2394)

• Interaction between signature deduction and new solver.
  • Implement async closure signature deduction #121857

Open questions (RFC 3668)

• Which syntax should we choose for bounds?
  • Decide on bounds syntax for async closures (RFC 3668) #128129

Related

• Async closures rfcs#3668
• rustdoc: support for async Fn* trait bounds #127227
• [EXPERIMENT] Rewrite closure-of-async to async-closure #127827