Add `must_use_without_reason` lint by skatromb · Pull Request #16592 · rust-lang/rust-clippy

skatromb · 2026-02-19T22:14:44Z

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PR addresses proposal for adding a lint that warns about a #[must_use] attribute that lacks a reason.
Fixes #16466

Updated after review

Rebased onto current master and addressed all review feedback. The branch is now a single commit.

Category style → restriction — the lint is opinionated and restricts an otherwise valid attribute.
Renamed must_use_without_note → must_use_without_reason, matching allow_attributes_without_reason. Diagnostic wording uses "reason" throughout.
Suggestion placeholder is now #[must_use = "<REASON>"] instead of "/* reason */".
must_use_candidate now suggests a message based on is_lint_allowed. By default it is unchanged from master — plain #[must_use], MachineApplicable. Only when must_use_without_reason is enabled at that node does it suggest #[must_use = "<REASON>"], so applying the fix does not immediately trip the other lint. Covered by a scoped module in tests/ui/must_use_candidates.rs, which keeps the existing cases and their .fixed output untouched.
in_external_macro guard moved after the item-kind check in all three entry points.

changelog: [must_use_without_reason]: add a lint that warns on #[must_use] attributes without a reason

github-actions · 2026-02-19T22:24:41Z

Lintcheck changes for f1289a9

Lint	Added	Removed	Changed
`clippy::must_use_candidate`	0	0	4654
`clippy::must_use_without_reason`	530	0	0

This comment will be updated if you push new changes

rustbot · 2026-02-27T21:19:02Z

r? @dswij

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Random selection from Jarcho, dswij, llogiq, samueltardieu

skatromb · 2026-03-15T12:35:39Z

@dswij Hello! Would you be able to review my PR, or should I choose another reviewer?

skatromb · 2026-03-27T08:53:52Z

r? @Jarcho
Picking other reviewer, since current doesn't respond

Jarcho

In addition to the category change this should also be named must_use_without_reason to match allow_attributes_without_reason.

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Jarcho · 2026-03-27T11:37:35Z

            "add the attribute",
-            format!("#[must_use]\n{indent}"),
-            Applicability::MachineApplicable,
+            format!("#[must_use = \"/* reason */\"] \n{indent}"),


This shouldn't be suggesting to add a reason in general. You can check if the new lint is enabled using is_lint_allowed and only suggest when it's needed.

rustbot · 2026-03-27T11:47:18Z

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

Jarcho · 2026-03-27T11:47:37Z

@rustbot label lint-nominated

rustbot · 2026-03-27T11:47:42Z

This lint has been nominated for inclusion.

A FCP topic has been created on Zulip.

Jarcho · 2026-07-13T12:36:32Z

Ping @skatromb. Do you plan to continue working on this?

skatromb · 2026-07-16T18:11:13Z

Hi, @Jarcho! I was bit stuck in another project, but will return to this PR in August, if this feels ok for you.

skatromb · 2026-07-30T11:37:33Z

@rustbot ready

skatromb · 2026-08-20T07:09:16Z

@samueltardieu @Jarcho Rebased on main, fixed your comments, please take a look

Warns on `#[must_use]` attributes with no accompanying message.

rustbot · 2026-09-19T13:11:11Z

This PR was rebased onto a different master 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.

skatromb · 2026-09-19T13:33:35Z

@samueltardieu @Jarcho Can you look at PR and approve if everything looks ok for you?

Jarcho

~~Minor thing with expansion checks. !from_expansion implies !in_external_macro with the former being notably faster.~~

Ignore this; I misread what was happening.

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Jarcho

Thank you.

@rustbot merge

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skatromb · 2026-09-19T21:02:19Z

Thank you! ❤️

rustbot added the needs-fcp PRs that add, remove, or rename lints and need an FCP label Feb 19, 2026

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samueltardieu reviewed Feb 22, 2026

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Comment thread clippy_lints/src/functions/mod.rs Outdated

skatromb force-pushed the must-use-without-note branch 3 times, most recently from dd76a0b to 3a164cc Compare February 27, 2026 17:36

skatromb marked this pull request as ready for review February 27, 2026 21:18

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Feb 27, 2026

rustbot assigned dswij Feb 27, 2026

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skatromb force-pushed the must-use-without-note branch from 3a164cc to 0aca2f3 Compare March 7, 2026 11:33

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skatromb force-pushed the must-use-without-note branch 2 times, most recently from 20eeb87 to 7354069 Compare March 7, 2026 17:40

rustbot assigned Jarcho and unassigned dswij Mar 27, 2026

Jarcho requested changes Mar 27, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Mar 27, 2026

rustbot added the lint-nominated Create an FCP-thread on Zulip for this PR label Mar 27, 2026

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skatromb force-pushed the must-use-without-note branch 3 times, most recently from 681cced to 16290b8 Compare July 30, 2026 11:27

skatromb marked this pull request as ready for review July 30, 2026 11:37

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Jul 30, 2026

skatromb requested a review from Jarcho July 30, 2026 11:38

rustbot removed the S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) label Jul 30, 2026

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skatromb force-pushed the must-use-without-note branch from 16290b8 to f3a4a6e Compare August 13, 2026 06:30

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skatromb force-pushed the must-use-without-note branch from f3a4a6e to 78e11b1 Compare August 20, 2026 06:59

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skatromb requested a review from samueltardieu August 20, 2026 07:08

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Add must_use_without_reason lint

f1289a9

Warns on `#[must_use]` attributes with no accompanying message.

skatromb force-pushed the must-use-without-note branch from 78e11b1 to f1289a9 Compare September 19, 2026 13:11

Jarcho requested changes Sep 19, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Sep 19, 2026

Jarcho approved these changes Sep 19, 2026

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rustbot added this pull request to the merge queue Sep 19, 2026

Merged via the queue into rust-lang:master with commit 9c1bd1f Sep 19, 2026
13 checks passed

skatromb deleted the must-use-without-note branch September 19, 2026 21:01

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skatromb commented Sep 19, 2026

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