Suggest removing `&` when awaiting a reference to a future by fru1tworld · Pull Request #154933 · rust-lang/rust

fru1tworld · 2026-04-07T08:18:41Z

When .awaiting &impl Future, suggest removing the & instead of removing .await.

rustbot · 2026-04-07T08:25:10Z

rustbot has assigned @JohnTitor.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 11 candidates

chenyukang · 2026-04-08T00:07:27Z

+error[E0277]: `&impl Future<Output = ()>` is not a future
+  --> $DIR/await-ref-future.rs:9:9
+   |
+LL |     fut.await;


View changes since the review

this test is the code from original issue, now suggest remove & not working for it.

as I referred, you may need to reuse the existing span-based borrow-removal logic (see suggest_remove_reference or extract it into a helper)

chenyukang · 2026-04-08T00:14:39Z

nit:

it's not necessary to request review after each commit, reviewer can receive notification from your git push, and will review it when time available(it's normal to wait several days since a lot of us working in free time). https://rustc-dev-guide.rust-lang.org/contributing.html?highlight=reviewer#waiting-for-reviews

request review may makes them feel too pushy.

fru1tworld · 2026-04-08T03:14:56Z

Updated to handle the additional cases:

let fut = &async_fn(); fut.await → suggest removing & from init
async fn bar(fut: &impl Future) → suggest removing & from param type (traces through async fn desugaring)
&dyn Future excluded (unsized)
Fallback help when specific span suggestion is unavailable

chenyukang · 2026-04-15T03:22:01Z

+                                // In async fn, params are desugared: `let fut = __arg0;`
+                                // with `LocalSource::AsyncFn`. Follow init back to the
+                                // original parameter.
+                                hir::Node::LetStmt(local)


This is still a fairly ad hoc reimplementation of borrow-removal logic, and it misses cases that the more general machinery should handle. For example, let fut = &&my_async_fn(); fut.await; still falls back to help: remove the .await. I think the better direction is to extract the borrow-peeling/span-finding part of suggest_remove_reference above and reuse it here, instead of open special handling for cases such as AddrOf / LetStmt / AsyncFn cases again.

View changes since the review

chenyukang · 2026-04-19T04:00:18Z

+                    }
+
+                    // Try removing `&` from the parameter type.
+                    if let Some(param) = terminal_param {


thanks, this version sees better.

this test should not suggest removing from parameter?

async fn ref_param_borrowed_expr(fut: &impl std::future::Future<Output = ()>) { (&fut).await; //~ ERROR is not a future }

View changes since the review

fru1tworld · 2026-04-20T10:06:49Z

Fixed — guarded param & removal with peeled_refs.is_empty() so it's skipped when the expression itself has &. Added test for the case.

chenyukang · 2026-04-21T00:42:30Z

Thanks!

@bors r=chenyukang

rust-bors · 2026-04-21T00:42:33Z

📌 Commit e9856d7 has been approved by chenyukang

It is now in the queue for this repository.

Rollup of 5 pull requests Successful merges: - #153411 (Offload slice support) - #154557 (Make E0284 generic argument suggestions more explicit) - #154933 (Suggest removing `&` when awaiting a reference to a future) - #155524 (Fix LLVM offload install docs to use semicolon-separated CMake lists) - #155568 (Update books)

Rollup of 5 pull requests Successful merges: - rust-lang/rust#153411 (Offload slice support) - rust-lang/rust#154557 (Make E0284 generic argument suggestions more explicit) - rust-lang/rust#154933 (Suggest removing `&` when awaiting a reference to a future) - rust-lang/rust#155524 (Fix LLVM offload install docs to use semicolon-separated CMake lists) - rust-lang/rust#155568 (Update books)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 7, 2026

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from f36f2b9 to 5afb519 Compare April 7, 2026 08:20

fru1tworld marked this pull request as ready for review April 7, 2026 08:25

rustbot 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 Apr 7, 2026

rustbot assigned JohnTitor Apr 7, 2026

chenyukang reviewed Apr 7, 2026

View reviewed changes

Comment thread compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

chenyukang reviewed Apr 7, 2026

View reviewed changes

Comment thread compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs Outdated

fru1tworld marked this pull request as draft April 7, 2026 12:03

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 Apr 7, 2026

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from bff3e3b to cdd3efa Compare April 7, 2026 12:08

fru1tworld marked this pull request as ready for review April 7, 2026 12:12

fru1tworld requested a review from chenyukang April 7, 2026 12:12

rustbot 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 Apr 7, 2026

chenyukang reviewed Apr 7, 2026

View reviewed changes

Comment thread tests/ui/async-await/await-ref-future.stderr Outdated

JohnTitor assigned chenyukang and unassigned JohnTitor Apr 7, 2026

fru1tworld marked this pull request as draft April 7, 2026 12:49

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 Apr 7, 2026

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from bc9d978 to 7e22d2d Compare April 7, 2026 23:17

This comment has been minimized.

Sign in to view

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from 7e22d2d to fe623c3 Compare April 7, 2026 23:33

fru1tworld marked this pull request as ready for review April 7, 2026 23:37

rustbot 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 Apr 7, 2026

fru1tworld requested a review from chenyukang April 7, 2026 23:37

chenyukang reviewed Apr 8, 2026

View reviewed changes

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from fe623c3 to 9aed706 Compare April 8, 2026 03:14

chenyukang reviewed Apr 15, 2026

View reviewed changes

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from 9aed706 to 1323164 Compare April 15, 2026 06:51

chenyukang reviewed Apr 19, 2026

View reviewed changes

Do not suggest removing param & when expr also has &

e9856d7

fru1tworld force-pushed the fix-87211-ref-future-diagnostic branch from 1323164 to e9856d7 Compare April 20, 2026 09:42

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 21, 2026

jhpratt mentioned this pull request Apr 21, 2026

Rollup of 5 pull requests #155576

Merged

rust-bors Bot merged commit 03dc6a3 into rust-lang:main Apr 21, 2026
11 checks passed

rustbot added this to the 1.97.0 milestone Apr 21, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Suggest removing `&` when awaiting a reference to a future#154933

Suggest removing `&` when awaiting a reference to a future#154933
rust-bors[bot] merged 1 commit intorust-lang:mainfrom
fru1tworld:fix-87211-ref-future-diagnostic

fru1tworld commented Apr 7, 2026 •

edited by rustbot

Loading

Uh oh!

rustbot commented Apr 7, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

This comment has been minimized.

chenyukang Apr 8, 2026 •

edited by rustbot

Loading

Uh oh!

chenyukang commented Apr 8, 2026

Uh oh!

fru1tworld commented Apr 8, 2026

Uh oh!

chenyukang Apr 15, 2026 •

edited by rustbot

Loading

Uh oh!

chenyukang Apr 19, 2026 •

edited by rustbot

Loading

Uh oh!

fru1tworld commented Apr 20, 2026

Uh oh!

chenyukang commented Apr 21, 2026

Uh oh!

rust-bors Bot commented Apr 21, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Uh oh!

Conversation

fru1tworld commented Apr 7, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Apr 7, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

This comment has been minimized.

chenyukang Apr 8, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

chenyukang commented Apr 8, 2026

Uh oh!

fru1tworld commented Apr 8, 2026

Uh oh!

chenyukang Apr 15, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

chenyukang Apr 19, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

fru1tworld commented Apr 20, 2026

Uh oh!

chenyukang commented Apr 21, 2026

Uh oh!

rust-bors Bot commented Apr 21, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

fru1tworld commented Apr 7, 2026 •

edited by rustbot

Loading

chenyukang Apr 8, 2026 •

edited by rustbot

Loading

chenyukang Apr 15, 2026 •

edited by rustbot

Loading

chenyukang Apr 19, 2026 •

edited by rustbot

Loading