Add manual_isolate_lowest_one lint by arunsingh · Pull Request #17037 · rust-lang/rust-clippy

arunsingh · 2026-05-19T15:13:42Z

changelog: new lint: [manual_isolate_lowest_one]

Adds a new manual_isolate_lowest_one lint for manual lowest-set-bit isolation patterns that can be written with .isolate_lowest_one().

This detects simple local expressions in the following forms:

x & x.wrapping_neg()
x.wrapping_neg() & x
x & -x for signed integers
-x & x for signed integers
nz.get() & nz.get().wrapping_neg() for NonZero<T> integer locals
nz.get() & -nz.get() for signed NonZero<T> integer locals

The implementation intentionally limits suggestions to simple local paths so rustfix does not change evaluation count for non-trivial expressions. For NonZero<T>::get() forms, the suggestion preserves the original primitive result type by using nz.isolate_lowest_one().get().

Validation:

cargo fmt
cargo check -p clippy_lints
TESTNAME=manual_isolate_lowest_one cargo uitest
cargo dev fmt --check
git diff --check

Note: cargo test --test dogfood was attempted locally but hit the existing Windows tikv_jemalloc_sys crate resolution issue before reaching a PR-specific failure. The focused lint UI test and clippy_lints check pass.

rustbot · 2026-05-19T15:13:49Z

r? @samueltardieu

rustbot has assigned @samueltardieu.
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: 7 candidates
7 candidates expanded to 7 candidates
Random selection from Jarcho, llogiq, samueltardieu

samueltardieu

Since the lint highest level operation is a BitAnd, it should probably belong to the operators module.

Also, please include tests where the various parts come from macros since you exclude them from the lint.

View changes since this review

rustbot · 2026-05-19T15:56:03Z

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

arunsingh · 2026-05-19T18:31:07Z

Addressed review feedback in 45572cf:

Moved manual_isolate_lowest_one into the operators module since the top-level operation is BitAnd.
Added macro-origin negative UI cases for the whole & expression, lhs, rhs, and unary negation forms.
Updated version/MSRV to 1.98.0 and category to complexity.
Moved the MSRV gate behind the structural/type checks.
Removed syntax-context plumbing and hir_with_context; matching now uses local ids and the diagnostic helper receives the span directly.

Verification run locally:

cargo check -p clippy_lints
TESTNAME=manual_isolate_lowest_one cargo uitest
cargo dev fmt --check
git diff --check

@rustbot ready

arunsingh · 2026-05-19T19:27:19Z

Added explicit MSRV compatibility coverage in manual_isolate_lowest_one UI tests:

#[clippy::msrv = 1.97] stays silent, so the lint does not suggest an API unavailable to older MSRV projects.
#[clippy::msrv = 1.98] lints and rustfixes to .isolate_lowest_one().

Local focused verification:

TESTNAME=manual_isolate_lowest_one cargo uitest
cargo check -p clippy_lints
cargo dev fmt --check
git diff --check

@rustbot ready

samueltardieu

NonZero support is intentionally left as follow-up work; this PR limits detection to primitive integer locals to keep the first implementation conservative and rustfix-safe.

Why would NonZero support add rustfix unsafety?

View changes since this review

arunsingh · 2026-05-21T10:23:24Z

Addressed the latest review in af1af72.

On NonZero<T>: agreed, my previous PR-body wording was imprecise. NonZero does not add rustfix unsafety for simple local .get() forms, so I added support for nz.get() & nz.get().wrapping_neg() / reversed order and signed nz.get() & -nz.get() / reversed order. The suggestion preserves the original primitive result type as nz.isolate_lowest_one().get().
On MSRV: updated the alias and lint metadata to 1.97.0, and changed the UI test boundary to verify 1.96 is silent while 1.97 lints.
I kept the non-simple-expression guard: calls such as next_nonzero_u32().get() & next_nonzero_u32().get().wrapping_neg() remain intentionally silent so rustfix does not change evaluation count.

Verification after the changes:

cargo fmt
cargo check -p clippy_lints
TESTNAME=manual_isolate_lowest_one cargo uibless
TESTNAME=manual_isolate_lowest_one cargo uitest
cargo dev fmt --check
git diff --check

@rustbot ready

samueltardieu

This lint should also be added to the list of lints that check the MSRV in clippy_config::conf.

View changes since this review

arunsingh · 2026-05-21T10:52:14Z

I have addressed the latest review in a9f8638.

based on @samueltardieu comments:

I had add manual_isolate_lowest_one to clippy_config::conf's msrv lint list so the generated config metadata correctly shows that this lint observes the msrv setting.
Replaced the duplicated primitive/NonZero diagnostic helpers with one emit_lint(..., add_get) helper, keeping the only behavior difference as the .get() suffix in the suggestion.
Switched from Sugg::hir to Sugg::hir_with_applicability, so if the source snippet cannot be recovered the suggestion is no longer reported as blindly machine-applicable.

Fresh verification after the patch:

cargo fmt
cargo dev fmt
cargo check -p clippy_lints
TESTNAME=manual_isolate_lowest_one cargo uitest
cargo dev fmt --check
git diff --chec

@rustbot ready

arunsingh · 2026-05-21T11:07:04Z

Small follow-up for CI: Clippy Test / base caught that book/src/lint_configuration.md needed to be regenerated after adding the lint to the msrv config list. I ran cargo bless --test config-metadata and amended the generated one-line book update in 029457bc14d0a2ab699a3b8c187d39d2c11573f2.

Additional verification:

cargo bless --test config-metadata
cargo dev fmt --check
git diff --check

samueltardieu · 2026-05-25T16:56:17Z

I kept the non-simple-expression guard: calls such as next_nonzero_u32().get() & next_nonzero_u32().get().wrapping_neg() remain intentionally silent so rustfix does not change evaluation count.

What do you mean by that?

(please no LLM-generated response, I'd like to speak to a human)

arunsingh · 2026-05-27T20:00:24Z

I kept the non-simple-expression guard: calls such as next_nonzero_u32().get() & next_nonzero_u32().get().wrapping_neg() remain intentionally silent so rustfix does not change evaluation count.

What do you mean by that?

(please no LLM-generated response, I'd like to speak to a human)

Sorry, I meant that the lint only handles locals because rewriting f().get() & f().get().wrapping_neg() to f().isolate_lowest_one().get() would call f() once instead of twice.

samueltardieu

Let's start the FCP.

@rustbot label lint-nominated

View changes since this review

rustbot · 2026-05-28T09:50:31Z

This lint has been nominated for inclusion.

A FCP topic has been created on Zulip.

arunsingh · 2026-05-28T17:49:46Z

I had addressed the review comments. please review @rustbot ready

Handled

rustbot assigned samueltardieu May 19, 2026

rustbot added needs-fcp PRs that add, remove, or rename lints and need an FCP S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels May 19, 2026

samueltardieu requested changes May 19, 2026

View reviewed changes

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 May 19, 2026

arunsingh force-pushed the add-manual-isolate-lowest-one branch 3 times, most recently from bdc6c6b to 45572cf Compare May 19, 2026 18:26

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 from the author. (Use `@rustbot ready` to update this status) labels May 19, 2026

arunsingh force-pushed the add-manual-isolate-lowest-one branch from 45572cf to 4525d1b Compare May 19, 2026 19:26

samueltardieu requested changes May 20, 2026

View reviewed changes

Comment thread clippy_utils/src/msrvs.rs Outdated

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 May 20, 2026

arunsingh force-pushed the add-manual-isolate-lowest-one branch from 4525d1b to af1af72 Compare May 21, 2026 10:13

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 from the author. (Use `@rustbot ready` to update this status) labels May 21, 2026

samueltardieu requested changes May 21, 2026

View reviewed changes

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs Outdated

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs Outdated

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 May 21, 2026

arunsingh force-pushed the add-manual-isolate-lowest-one branch from af1af72 to a9f8638 Compare May 21, 2026 10:51

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 from the author. (Use `@rustbot ready` to update this status) labels May 21, 2026

arunsingh force-pushed the add-manual-isolate-lowest-one branch from a9f8638 to 029457b Compare May 21, 2026 11:06

samueltardieu requested changes May 28, 2026

View reviewed changes

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs Outdated

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

ada4a previously requested changes May 28, 2026

View reviewed changes

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs Outdated

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs

ada4a reviewed May 28, 2026

View reviewed changes

Comment thread clippy_lints/src/operators/manual_isolate_lowest_one.rs Outdated

Add manual_isolate_lowest_one lint

b8953cb

arunsingh force-pushed the add-manual-isolate-lowest-one branch from 029457b to b8953cb Compare May 28, 2026 17:45

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 from the author. (Use `@rustbot ready` to update this status) labels May 28, 2026

samueltardieu approved these changes Jun 4, 2026

View reviewed changes

samueltardieu added this pull request to the merge queue Jun 4, 2026

Merged via the queue into rust-lang:master with commit 9e94337 Jun 4, 2026
11 checks passed

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Jun 4, 2026

Conversation

arunsingh commented May 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented May 19, 2026

Uh oh!

samueltardieu left a comment • 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!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

rustbot commented May 19, 2026

Uh oh!

arunsingh commented May 19, 2026

Uh oh!

arunsingh commented May 19, 2026

Uh oh!

samueltardieu left a comment • 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!

Uh oh!

arunsingh commented May 21, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

samueltardieu left a comment • 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!

Uh oh!

Uh oh!

arunsingh commented May 21, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

arunsingh commented May 21, 2026

Uh oh!

samueltardieu commented May 25, 2026

Uh oh!

arunsingh commented May 27, 2026

Uh oh!

samueltardieu left a comment • 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!

Uh oh!

Uh oh!

rustbot commented May 28, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

arunsingh commented May 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

arunsingh commented May 19, 2026 •

edited

Loading

samueltardieu left a comment •

edited by rustbot

Loading

samueltardieu left a comment •

edited by rustbot

Loading

arunsingh commented May 21, 2026 •

edited

Loading

samueltardieu left a comment •

edited by rustbot

Loading

arunsingh commented May 21, 2026 •

edited

Loading

samueltardieu left a comment •

edited by rustbot

Loading

arunsingh commented May 28, 2026 •

edited

Loading