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Make inline attributes apply to the generated poll in async fn - #149245

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Make inline attributes apply to the generated poll in async fn#149245
xacrimon wants to merge 1 commit into
rust-lang:mainfrom
xacrimon:acrimon/async-fn-inline-attr

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@xacrimon

@xacrimonxacrimon commented Nov 23, 2025•
edited by JonathanBrouwer
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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)]pubasyncfnhi() -> i32{1337}pubfnconsumer(cx:&mutContext<'_>) -> 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

@rustbotrustbot 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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xacrimonforce-pushed the acrimon/async-fn-inline-attr branch from 46d6c3e to d89022aCompareNovember 23, 2025 20:55
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xacrimonforce-pushed the acrimon/async-fn-inline-attr branch 5 times, most recently from 9478bfd to fa35f7bCompareNovember 23, 2025 23:25
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@JonathanBrouwer

JonathanBrouwer commented Nov 25, 2025

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@rustbot author
CI is failing

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

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bors commented Dec 11, 2025

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

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rust-borsBot commented Jan 2, 2026

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

@Mark-SimulacrumMark-Simulacrum added the relnotes Marks issues that should be documented in the release notes of the next release. label Jan 25, 2026
@rustbotrustbot mentioned this pull request Jan 25, 2026
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@Enselic

Enselic commented Mar 20, 2026

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Triage: Are you still working on this @xacrimon?

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xacrimonforce-pushed the acrimon/async-fn-inline-attr branch from fa35f7b to 7054408CompareApril 5, 2026 16:59
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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.

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rust-borsBot commented May 12, 2026

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

@Dylan-DPCDylan-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
JonathanBrouwer requested changes Jun 21, 2026
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Comment threadcompiler/rustc_ast_lowering/src/expr.rs
let filtered_attrs = self.arena.alloc_from_iter(filtered_iter);

if filtered_attrs.is_empty() {
self.attrs.remove(&outer_hir_id.local_id);

@JonathanBrouwerJonathanBrouwerJun 21, 2026•
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Is this code reachable with the early-return above?

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Comment threadcompiler/rustc_ast_lowering/src/expr.rs
if filtered_attrs.is_empty() {
self.attrs.remove(&outer_hir_id.local_id);
} else {
self.attrs.insert(outer_hir_id.local_id, filtered_attrs);

@JonathanBrouwerJonathanBrouwerJun 21, 2026•
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Why are we overriding the attrs from outer_hir_id here?

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Comment threadcompiler/rustc_ast_lowering/src/expr.rs
);

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

@JonathanBrouwerJonathanBrouwerJun 21, 2026•
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Could you add some tests for this feature?

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@JonathanBrouwerJonathanBrouwerJun 21, 2026•
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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?

@rustbotrustbot 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
@JonathanBrouwer

JonathanBrouwer commented Jun 21, 2026•
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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

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A-attributesArea: Attributes (`#[…]`, `#![…]`)relnotesMarks issues that should be documented in the release notes of the next release.S-waiting-on-authorStatus: This is awaiting some action (such as code changes or more information) from the author.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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Successfully merging this pull request may close these issues.

#[inline(never)] does not work for async functions #[inline(never)] does not work for async fn

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