Prior to stabilization, we need to decide which syntax to use for async closure bounds. This was left as an open question in RFC 3668.

The main known candidates are:

• F: async FnMut() -> T
• F: AsyncFnMut() -> T

Other candidates discussed have included:

• F: async mut fn() -> T
• F: async mut () -> T
• F: async mut || -> T
• F: async fn(&mut self) -> T
• F: AsyncFn(&mut self) -> T
• F: async |&mut self| -> T

Tracking:

• Tracking issue for #![feature(async_closure)] (RFC 2394 / RFC 3668) #62290

@rustbot labels +T-lang +I-lang-nominated

cc @compiler-errors @rust-lang/lang