Fix unused_parens for pinned reference patterns by P8L1 · Pull Request #156089 · rust-lang/rust

P8L1 · 2026-05-02T14:23:58Z

The unused_parens lint previously treated pinned shared-reference patterns like plain shared-reference patterns when deciding whether removing parentheses could change the meaning of a leading mut binding.

That was too conservative for pinned reference patterns such as &pin const (mut x). The pin const part belongs to the outer reference pattern, so removing the inner parentheses still leaves mut x as the subpattern.

This updates the ambiguity check so the leading-mut suppression only applies to plain shared reference patterns. Pinned reference patterns can now receive correct rustfix suggestions.

The patch also broadens the binding check from only plain mut bindings to all binding modes whose binding mutability is Mutability::Mut, covering forms such as mut ref pin const.

@rustbot label F-pin_ergonomics

rustbot · 2026-05-02T14:24:02Z

r? @nnethercote

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Kivooeo · 2026-05-03T00:56:35Z

same as here: #156087 (comment)

@rustbot author

rustbot · 2026-05-03T00:56:38Z

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

P8L1 · 2026-05-03T11:10:06Z

same as here: #156087 (comment)

@rustbot author

I gated the pinned-pattern unused-parens rustfix path on pin_ergonomics, so it is only emitted for crates that opted into the feature. I also left a FIXME next to the gate saying to remove it once pin_ergonomics is stabilized.

P8L1 · 2026-05-03T11:39:06Z

@rustbot ready

Addressed the review feedback by gating the pinned-pattern unused_parens rustfix path on pin_ergonomics, so it is only emitted for crates that opted into the feature.

I also added a FIXME next to the gate saying to remove it once pin_ergonomics is stabilized.

P8L1 · 2026-05-03T16:55:48Z

r? @Kivooeo

P8L1 · 2026-05-04T20:32:57Z

@Kivooeo Please review this as well

Kivooeo · 2026-05-04T20:37:26Z

it's been only two days since it's open, review may take up to two weeks

since i'm pretty busy with other stuff i'd ask you to wait, because it may take a little longer

P8L1 · 2026-05-16T08:55:28Z

Hey @Kivooeo, just wanted to gently bump this since it’s been about two weeks.

I think I’ve addressed the previous feedback, but please let me know if there’s anything else you’d like changed.

Thanks!

Kivooeo

looks fine to me, but some nits

View changes since this review

rustbot · 2026-05-17T15:21:28Z

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.

P8L1 · 2026-05-17T15:56:04Z

@Kivooeo ready
I addressed all the nits and squashed to 1 commit

P8L1 · 2026-05-28T16:28:32Z

@Kivooeo Hi, sorry for the ping, it's been another 2 weeks. Is there a chance you could have another look? I have addressed the nits

Kivooeo · 2026-05-29T09:08:47Z

I'll review today-tomorrow

Kivooeo · 2026-05-30T14:48:47Z

Got very busy today, will review tomorrow 100%, sorry for a delay

P8L1 · 2026-05-30T16:02:00Z

Got very busy today, will review tomorrow 100%, sorry for a delay

Ok thanks so much, I appreciate you!

P8L1 · 2026-05-31T14:16:58Z

@Kivooeo I addressed the comment concerns

Kivooeo · 2026-06-03T08:37:04Z

@bors r+ rollup

rust-bors · 2026-06-03T08:37:07Z

📌 Commit 9849fa8 has been approved by Kivooeo

It is now in the queue for this repository.

@rustbot

…erns, r=Kivooeo Fix unused_parens for pinned reference patterns The unused_parens lint previously treated pinned shared-reference patterns like plain shared-reference patterns when deciding whether removing parentheses could change the meaning of a leading `mut` binding. That was too conservative for pinned reference patterns such as `&pin const (mut x)`. The `pin const` part belongs to the outer reference pattern, so removing the inner parentheses still leaves `mut x` as the subpattern. This updates the ambiguity check so the leading-`mut` suppression only applies to plain shared reference patterns. Pinned reference patterns can now receive correct rustfix suggestions. The patch also broadens the binding check from only plain `mut` bindings to all binding modes whose binding mutability is `Mutability::Mut`, covering forms such as `mut ref pin const`. @rustbot label F-pin_ergonomics

@rustbot

…erns, r=Kivooeo Fix unused_parens for pinned reference patterns The unused_parens lint previously treated pinned shared-reference patterns like plain shared-reference patterns when deciding whether removing parentheses could change the meaning of a leading `mut` binding. That was too conservative for pinned reference patterns such as `&pin const (mut x)`. The `pin const` part belongs to the outer reference pattern, so removing the inner parentheses still leaves `mut x` as the subpattern. This updates the ambiguity check so the leading-`mut` suppression only applies to plain shared reference patterns. Pinned reference patterns can now receive correct rustfix suggestions. The patch also broadens the binding check from only plain `mut` bindings to all binding modes whose binding mutability is `Mutability::Mut`, covering forms such as `mut ref pin const`. @rustbot label F-pin_ergonomics

…uwer Rollup of 15 pull requests Successful merges: - #155763 (Promotes 5 Thumb-mode bare-metal Arm targets to Tier 2) - #156953 (delegation: emit error when there is an infer lifetime in user-specified args) - #157248 (delegation: move statements out of the first arg) - #157263 (rustc_codegen_ssa: Refactor `ArchiveEntry` to include entry kind) - #157311 (Use weak linkage for EII defaults) - #156089 (Fix unused_parens for pinned reference patterns) - #156928 (Remove -Zemscripten-wasm-eh) - #157236 (Reorganize `tests/ui/issues` [3/N]) - #157287 (Const generics: remove AliasTerm::kind(), and small fixes) - #157294 (Split coroutine layout computation to its own file) - #157328 (windows: Elide division-by-zero checks in Instant::now()) - #157331 (Rewrite target checking for `#[link]`) - #157336 (Enable `clippy::mem_replace_with_default`) - #157362 (Fix trivial wf module argument/doc comment name mismatches) - #157364 (Rewrite target checking of `rustc_dummy`) Failed merges: - #157332 (Rewrite target checking for `#[sanitize]`)

@rustbot

Rollup merge of #156089 - P8L1:fix-unused-parens-pinned-patterns, r=Kivooeo Fix unused_parens for pinned reference patterns The unused_parens lint previously treated pinned shared-reference patterns like plain shared-reference patterns when deciding whether removing parentheses could change the meaning of a leading `mut` binding. That was too conservative for pinned reference patterns such as `&pin const (mut x)`. The `pin const` part belongs to the outer reference pattern, so removing the inner parentheses still leaves `mut x` as the subpattern. This updates the ambiguity check so the leading-`mut` suppression only applies to plain shared reference patterns. Pinned reference patterns can now receive correct rustfix suggestions. The patch also broadens the binding check from only plain `mut` bindings to all binding modes whose binding mutability is `Mutability::Mut`, covering forms such as `mut ref pin const`. @rustbot label F-pin_ergonomics

rustbot assigned nnethercote May 2, 2026

rustbot added 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 May 2, 2026

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 3, 2026

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label May 3, 2026

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 May 3, 2026

rustbot assigned Kivooeo and unassigned nnethercote May 3, 2026

Kivooeo reviewed May 17, 2026

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Comment thread compiler/rustc_lint/src/unused.rs Outdated

Comment thread compiler/rustc_lint/src/unused.rs Outdated

Comment thread tests/ui/lint/unused-parens-pinned-reference-patterns.fixed

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P8L1 force-pushed the fix-unused-parens-pinned-patterns branch from 696ca4a to 582523b Compare May 17, 2026 15:21

Fix unused_parens for pinned reference patterns

ffe1dba

P8L1 force-pushed the fix-unused-parens-pinned-patterns branch from 582523b to ffe1dba Compare May 17, 2026 19:13

rustbot added the F-pin_ergonomics `#![feature(pin_ergonomics)]` label May 22, 2026

P8L1 requested a review from Kivooeo May 23, 2026 15:43

Kivooeo reviewed May 31, 2026

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Comment thread compiler/rustc_lint/src/unused.rs Outdated

Adress concerns

9849fa8

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 Jun 3, 2026

JonathanBrouwer mentioned this pull request Jun 3, 2026

Rollup of 9 pull requests #157372

Closed

This was referenced Jun 3, 2026

Rollup of 15 pull requests #157375

Closed

Rollup of 15 pull requests #157376

Merged

rust-bors Bot merged commit 4014db7 into rust-lang:main Jun 3, 2026
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rustbot added this to the 1.98.0 milestone Jun 3, 2026

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