Async closure argument inference is broken with functions taking FnOnce() -> futures::TryFuture #127781
Description
I'm writing this as a continuation of #127425
While the problem from first message in issue seems to be fixed, there are still cases when this fails.
One of examples is when using try_for_each instead of for_each, when closure is expected to return Result:
#![feature(async_closure)] use anyhow::Error; use futures::{stream::repeat_with, StreamExt, TryStreamExt}; fn accept_str(_: &str) {} fn accept_string(_: &String) {} #[tokio::main(flavor = "current_thread")] async fn main() -> Result<(), Error> { repeat_with(|| "foo".to_owned()) .take(1) .map(Result::<_, Error>::Ok) .try_for_each(async move |value| { // error on whole closure, rust thinks that type of value is `str` accept_str(&value); // type annotations needed, cannot infer type accept_str(value.as_str()); // this works accept_string(&value); // ok Ok(()) }) .await?; Ok(()) }I expected to see this happen: All options used to work in past versions of rust
Instead, this happened: Without explicit type hint it fails
Version it worked on
It most recently worked on: Not 100% sure, some explanations have been made in original issue
Version with regression
rustc 1.81.0-nightly (d9284afea 2024-07-14) binary: rustc commit-hash: d9284afea99e0969a0e692b9e9fd61ea4ba21366 commit-date: 2024-07-14 host: x86_64-pc-windows-msvc release: 1.81.0-nightly LLVM version: 18.1.7