Tracking Issue for feature future_poll_fn

[yoshuawuyts]

The feature gate for the issue is #![feature(future_poll_fn)].

Steps

• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (Stabilize future_poll_fn #99306)

Unresolved Questions

• Should this be named future::from_fn instead?

Implementation history

• Initial implementation in Add core::future::{poll_fn, PollFn} #72303
• Rename from future::poll_fn to future::from_fn in Rename core::future::poll_fn to core::future::from_fn #76789
  • closed as it's ambiguous, see the discussion on that PR

[joshtriplett]

This exists in futures-lite, and people use it. It seems worth having available in the standard library.

The naming discussion doesn't seem likely to change, and all else being equal there's a history for the name poll_fn.

Shall we stabilize this?

@rfcbot merge

[rfcbot]

Team member @joshtriplett has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[RalfJung]

There are some soundness issues with poll_fn (not strictly speaking a soundness bug, but we might still want to do a breaking change now before there are too many people relying on this): the fact that PollFn<F> is always Unpin is a problem. It should require F: Unpin for that.

See IRLO for details, in particular this miscompilation bug.

[RalfJung]

I am proposing to change the Unpin impl in #102737.