Make inline attributes apply to the generated `poll` in async fn by xacrimon · Pull Request #149245 · rust-lang/rust

xacrimon · 2025-11-23T20:50:06Z

This PR adds lowering code (similar to how track_caller forwarding works) to async fn items and async || closures such that any inline attributes put on them are inherited by the generated coroutine (corresponding to the poll() implementation) and are not applied to the outer function. This behavior matches the accepted FCP in the first linked issue.

Code like the following now correctly codegen 3 functions

async_fn_test::consumer
async_fn_test::hi::{closure#0}
core::ptr::drop_in_place::<async_fn_test::hi::{closure#0}>

#[inline(never)]
pub async fn hi() -> i32 {
    1337
}

pub fn consumer(cx: &mut Context<'_>) -> Option<i32> {
    let fut = hi();
    let pinned = pin!(fut);
    match pinned.poll(cx) {
        Poll::Ready(value) => Some(value),
        Poll::Pending => None,
    }
}

Fixes #129347 and fixes #106765.

This has already been FCP'ed here: #129347

rustbot · 2025-11-23T20:50:11Z

r? @JonathanBrouwer

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JonathanBrouwer · 2025-11-25T18:49:27Z

@rustbot author
CI is failing

rustbot · 2025-11-25T18:49:32Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

bors · 2025-12-11T00:38:38Z

☔ The latest upstream changes (presumably #149853) made this pull request unmergeable. Please resolve the merge conflicts.

rust-bors · 2026-01-02T16:32:01Z

☔ The latest upstream changes made this pull request unmergeable. Please resolve the merge conflicts.

Enselic · 2026-03-20T21:10:39Z

Triage: Are you still working on this @xacrimon?

… instead of the desugared creator function.

rustbot · 2026-04-05T16:59:33Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

rust-bors · 2026-05-12T01:55:28Z

☔ The latest upstream changes (presumably #156473) made this pull request unmergeable. Please resolve the merge conflicts.

JonathanBrouwer · 2026-06-21T13:17:43Z

+        let filtered_attrs = self.arena.alloc_from_iter(filtered_iter);
+
+        if filtered_attrs.is_empty() {
+            self.attrs.remove(&outer_hir_id.local_id);


Is this code reachable with the early-return above?

View changes since the review

JonathanBrouwer · 2026-06-21T13:19:54Z

+        if filtered_attrs.is_empty() {
+            self.attrs.remove(&outer_hir_id.local_id);
+        } else {
+            self.attrs.insert(outer_hir_id.local_id, filtered_attrs);


Why are we overriding the attrs from outer_hir_id here?

View changes since the review

JonathanBrouwer · 2026-06-21T13:20:05Z

                );

                this.maybe_forward_track_caller(body.span, closure_hir_id, expr.hir_id);
+                this.forward_inline(body.span, closure_hir_id, expr.hir_id);


Could you add some tests for this feature?

View changes since the review

From the lang team decision:

We talked about this in the lang call today. We want attributes like this to apply to "where the code is", i.e. to the poll function in this case. The wrapper function, on the other hand, should always be inlined.

Make sure your tests cover this.
I suspect the wrapper function is already marked as inline somewhere, if it is not could you or someone else open a separate PR that does this?

JonathanBrouwer · 2026-06-21T13:21:45Z

Sorry for taking so long to review this PR! This PR fell of my radar, thanks @Dylan-DPC for fixing up the label so I saw it again

rustbot assigned JonathanBrouwer Nov 23, 2025

rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 23, 2025

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xacrimon force-pushed the acrimon/async-fn-inline-attr branch from 46d6c3e to d89022a Compare November 23, 2025 20:55

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xacrimon force-pushed the acrimon/async-fn-inline-attr branch 5 times, most recently from 9478bfd to fa35f7b Compare November 23, 2025 23:25

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 25, 2025

Mark-Simulacrum added the relnotes Marks issues that should be documented in the release notes of the next release. label Jan 25, 2026

rustbot mentioned this pull request Jan 25, 2026

Tracking issue for release notes of #149245: Make inline attributes apply to the generated poll in async fn #151655

Open

Inline attributes on async fn and async closures affect the poll impl…

7054408

… instead of the desugared creator function.

xacrimon force-pushed the acrimon/async-fn-inline-attr branch from fa35f7b to 7054408 Compare April 5, 2026 16:59

Dylan-DPC added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 16, 2026

JonathanBrouwer requested changes Jun 21, 2026

View reviewed changes

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 21, 2026

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xacrimon commented Nov 23, 2025 •

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