62d1574876
[wg-async-await] Drop `async fn` arguments in async block Fixes #54716. This PR modifies the HIR lowering (and some other places to make this work) so that unused arguments to a async function are always dropped inside the async move block and not at the end of the function body. ``` async fn foo(<pattern>: <type>) { async move { } } // <-- dropped as you "exit" the fn // ...becomes... fn foo(__arg0: <ty>) { async move { let <pattern>: <ty> = __arg0; } // <-- dropped as you "exit" the async block } ``` However, the exact ordering of drops is not the same as a regular function, [as visible in this playground example](https://play.rust-lang.org/?version=stable&mode=debug&edition=2015&gist=be39af1a58e5d430be1eb3c722cb1ec3) - I believe this to be an unrelated issue. There is a [Zulip topic](https://rust-lang.zulipchat.com/#narrow/stream/187312-t-compiler.2Fwg-async-await/topic/.2354716.20drop.20order) for this. r? @cramertj cc @nikomatsakis