---
title: WG-async triage meeting 2024-09-05
tags: ["WG-async", "triage-meeting", "minutes"]
date: 2024-09-05
discussion: https://rust-lang.zulipchat.com/#narrow/stream/187312-wg-async/topic/Meeting.202024-09-05
url: https://hackmd.io/p6wmagFSTayvApW8rx3Akw
---

# WG-async meeting agenda

- Meeting date: 2024-09-05

## Attendance

- People: TC, Yosh, eholk

## Meeting roles

- Minutes: TC

## Scheduled meetings

None.

Update these [here](https://github.com/orgs/rust-lang/projects/40/views/1).

## Proposed meetings

None.

Update these [here](https://github.com/orgs/rust-lang/projects/40/views/1).

## Announcements or custom items

(Meeting attendees, feel free to add items here!)

## Scheduling for September

- 12th: No meeting, RustConf
- 19th
- Reorganizing WG-async.
- 26th: No meeting.

Suggestions:

- Can we help unblock async closure syntax?
- Probably not much we can do here.
- Unsafe lifetime binders?
- Also probably not much to do yet?
- wg-async button pressing to create T-lang-async-advisors
- Write an RFC together?

## Untriaged issues

### "Misleading help suggests `Sync` bound when shareable reference is passed across or into await" rust#129105

**Link:** https://github.com/rust-lang/rust/issues/129105

fn spawn<F: Future + Send + 'static>(_: F) {}

fn spawn_task<T: Send + 'static>(mut state: T) {
    spawn(async move {
        let x = &mut state; // <-- Remove `mut` for error.
        async move { _ = [x] }.await;
    });
}

fn main() {}

trait AllSend<'a, T: 'a + ?Sized>
where
    &'a mut T: Send,
{
}

impl<'a, T: ?Sized + Send + 'a> AllSend<'a, T> for T {}

Proposed responses:

---

This is a cool technique to work around this issue! It seems like in general the `Sync` bound is going to be the "more correct" solution, so I wouldn't want to remove that from the suggestion. Then the question is whether to also suggest using a mutable reference. This is already a long error message, so we want to avoid making it longer and likely more confusing. In most cases it seems better to treat this mutable reference as an advanced technique.

---

@rustbot labels +AsyncAwait-Triaged -needs-triage

Interesting. We talked about this today in WG-async triage.

We minimized the issue as follows:

fn spawn<F: Future + Send + 'static>(_: F) {}

fn spawn_task<T: Send + 'static>(mut state: T) {
    spawn(async move {
        let x = &mut state; // <-- Remove `mut` for error.
        async move { _ = [x] }.await;
    });
}

fn main() {}

We also wrote this to demonstrate the interesting behavior of `&mut` here:

trait AllSend<'a, T: 'a + ?Sized>
where
    &'a mut T: Send, // <-- Remove `mut` to get error.
{
}

impl<'a, T: ?Sized + Send + 'a> AllSend<'a, T> for T {}

Overall, we felt in general that adding the `Sync` bound is going to be the right thing to do in most cases. We were skeptical about how generalizable the suggestion of threading `mut` throughout would be. We think the error message might just get too long if we were to try to suggest `mut` here, so we think things are probably fine as-is. Using `mut` to solve the problem here is a bit of a subtle technique.

(The meeting ended here.)

### "#[inline(never)] does not work for async functions" rust#129347

**Link:** https://github.com/rust-lang/rust/issues/129347

### "async code fails to compile with `-Znext-solver`" rust#129865

**Link:** https://github.com/rust-lang/rust/issues/129865

### "Add LocalWaker support" libs-team#191

**Link:** https://github.com/rust-lang/libs-team/issues/191

### "Context reactor hook" libs-team#347

**Link:** https://github.com/rust-lang/libs-team/issues/347

## Nominated RFCs, PRs, and issues

### "Generic Futures" rfcs#3434

**Link:** https://github.com/rust-lang/rfcs/pull/3434

### "Tracking Issue for `task::Waker::noop`" rust#98286

**Link:** https://github.com/rust-lang/rust/issues/98286

### "Rename `AsyncIterator` back to `Stream`, introduce an AFIT-based `AsyncIterator` trait" rust#119550

**Link:** https://github.com/rust-lang/rust/pull/119550

### "Clarification needed on what happens when `Future::poll` wakes an old waker" rust#119698

**Link:** https://github.com/rust-lang/rust/issues/119698

### "Overly conservative async capture analysis when values are borrowed" rust#129325

**Link:** https://github.com/rust-lang/rust/issues/129325

### "Context reactor hook" libs-team#347

**Link:** https://github.com/rust-lang/libs-team/issues/347

## WG RFCs, PRs, and issues nominated for T-lang/T-types

None.

## Pending PRs on the WG-async repo

None.

## `S-waiting-on-team`

### "Rename `AsyncIterator` back to `Stream`, introduce an AFIT-based `AsyncIterator` trait" rust#119550

**Link:** https://github.com/rust-lang/rust/pull/119550

## Proposed FCPs

**Check your boxes!**

None.

## Active FCPs

None.

## P-critical issues

None.

## WG-async work project board

https://github.com/orgs/rust-lang/projects/29/views1/d