Add [`manual_ilog2`] lint#13331

Sour1emon · 2024-09-01T19:13:12Z

changelog: new lint: [manual_ilog2]

Suggest using ilog2() instead of the manual implementations for some basic cases

rustbot · 2024-09-01T19:13:17Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Jarcho (or someone else) some time within the next two weeks.

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alex-semenyuk · 2024-09-02T18:13:11Z

tests/ui/manual_ilog2.fixed

+    let b: u64 = 543534;
+    let _ = b.ilog2();
+
+    let _ = 64 - b.leading_zeros(); // No lint


Is it check // No lint

Suppose no need to check this additionally

The manual ilog2 implementation is bit_width - 1 - x.leading_zeros() so this is just making sure that any other constant besides bit_width - 1 does not lint.

clippy_lints/src/manual_ilog2.rs

bors · 2024-09-03T17:46:39Z

☔ The latest upstream changes (presumably #13247) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2024-09-05T23:29:41Z

☔ The latest upstream changes (presumably #12987) made this pull request unmergeable. Please resolve the merge conflicts.

Jarcho

This will need macro checks. in_external_macro combined with context checks should work (span.ctxt() should be the same for all involved expressions).

Otherwise just a couple of small nits and the test looks like it needs to be re-blessed..

Jarcho · 2024-09-11T16:58:36Z

clippy_lints/src/manual_ilog2.rs

+        if !self.msrv.meets(msrvs::MANUAL_ILOG2) {
+            return;
+        }
+        let mut applicability = Applicability::MachineApplicable;


It's better to check the HIR tree first.

Jarcho · 2024-09-11T17:00:02Z

clippy_lints/src/manual_ilog2.rs

+        }
+
+        if let ExprKind::MethodCall(method_name, reciever, args, _) = expr.kind
+            && method_name.ident.as_str() == "ilog"


The string check should be moved to after others. It requires locking the symbol table.

Jarcho · 2024-09-11T17:00:43Z

clippy_lints/src/manual_ilog2.rs

+            }
+        }
+
+        if let ExprKind::MethodCall(method_name, reciever, args, _) = expr.kind


Use [arg] instead to save the length check later.

Jarcho · 2024-09-11T17:12:12Z

clippy_lints/src/manual_ilog2.rs

+            && args.len() == 1
+            && let ExprKind::Lit(lit) = args[0].kind
+            && let LitKind::Int(Pu128(2), _) = lit.node
+            && cx.typeck_results().expr_ty(reciever).is_integral()


This should be a check for an inherent method rather than just a type check (could be a trait function with the same name). You can add is_inherent_method_call.

Jarcho · 2024-09-11T17:20:14Z

clippy_lints/src/manual_ilog2.rs

+            && let ExprKind::Lit(lit) = left.kind
+            && let LitKind::Int(Pu128(val), _) = lit.node
+            && let ExprKind::MethodCall(method_name, reciever, _, _) = right.kind
+            && method_name.ident.as_str() == "leading_zeros"


This will also need a check for an inherent method.

bors · 2024-09-22T14:35:39Z

☔ The latest upstream changes (presumably #13322) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2024-10-13T07:49:14Z

☔ The latest upstream changes (presumably #13334) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-03-31T23:42:06Z

☔ The latest upstream changes (possibly d28d234) made this pull request unmergeable. Please resolve the merge conflicts.

Jarcho · 2025-05-21T20:09:04Z

Ping @Sour1emon from triage. Do you intend to keep working on this?

Sour1emon · 2025-07-12T21:11:03Z

At the moment I do not have time to finish it.

Revival of #13331 Part of #12894 changelog: [`manual_ilog2`]: new lint

rustbot assigned Jarcho Sep 1, 2024

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Sep 1, 2024

Sour1emon force-pushed the manual_ilog2_lint branch 2 times, most recently from 1de3240 to 9a9bd69 Compare September 1, 2024 20:41

alex-semenyuk reviewed Sep 2, 2024

View reviewed changes

clippy_lints/src/manual_ilog2.rs Outdated Show resolved Hide resolved

Sour1emon force-pushed the manual_ilog2_lint branch from 839539b to 8107d51 Compare September 4, 2024 00:47

Sour1emon force-pushed the manual_ilog2_lint branch from 8107d51 to fc5f870 Compare September 7, 2024 17:32

Jarcho requested changes Sep 11, 2024

View reviewed changes

Sour1emon added 6 commits September 26, 2024 18:30

Add [manual_ilog2] lint

b97f731

Added extract_msrv_attr macro to manual_ilog2.rs

3781026

Add semicolons

40cd0f8

Improve "Why is this bad" section and inline sugg variable

a9a385c

Extract suggestions to seperate function

51be384

Updated test comment

bd65f17

Sour1emon force-pushed the manual_ilog2_lint branch from a0ba2b5 to bd65f17 Compare September 27, 2024 01:31

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 31, 2025

Jarcho closed this Sep 17, 2025

ada4a mentioned this pull request Oct 11, 2025

feat(manual_ilog2): new lint #15865

Merged

github-merge-queue bot pushed a commit that referenced this pull request Dec 2, 2025

feat(manual_ilog2): new lint (#15865)

a10cafe

Revival of #13331 Part of #12894 changelog: [`manual_ilog2`]: new lint

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