fix(linter): don't simplify logic expressions with right-side boolean literals by FrankFMY · Pull Request #8976 · biomejs/biome

FrankFMY · 2026-02-05T17:24:09Z

AI disclosure: This PR was authored with the assistance of Claude (Anthropic). Claude helped explore the codebase, analyze the issue, implement the fix, write tests, and prepare the PR.

Summary

Fixes #8577. The useSimplifiedLogicExpression rule incorrectly suggested removing boolean literals on the right side of logical expressions.

In JavaScript, logical operators (||, &&) return one of the operand values, not a boolean. Patterns like account?.test || false are intentional boolean coercion — || false ensures the result is always true or false rather than potentially undefined.

Removed simplification logic for right-side boolean literals in both || and && branches. Left-side simplifications (true && x, false || x) remain unchanged, since JS short-circuit semantics guarantee they are always safe.

Test Plan

cargo test -p biome_js_analyze -- use_simplified_logic_expression — 2 tests pass
cargo fmt -- --check — clean
Updated test cases: moved boolExp || true to valid, added x || false, x && true, x && false, and the original report case account?.test || false

Docs

No documentation changes needed — the rule behavior is corrected to match its documented intent.

… literals Fixes biomejs#8577. The `useSimplifiedLogicExpression` rule incorrectly suggested removing boolean literals on the right side of logical expressions (e.g. `x || false` → `x`). In JavaScript, logical operators return operand values rather than booleans, so `x || false` serves as a boolean coercion pattern and is not redundant. Only simplify when the boolean literal is on the left side, where JS short-circuit semantics guarantee correctness.

changeset-bot · 2026-02-05T17:24:15Z

🦋 Changeset detected

Latest commit: 606e92c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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coderabbitai · 2026-02-05T17:27:20Z

Walkthrough

This change updates the useSimplifiedLogicExpression lint rule to stop proposing simplifications when a boolean literal appears on the right-hand side of a logical expression. Redundant right-side boolean-literal handling was removed from both OR and AND branches so only left-side boolean-literal simplifications are performed. Tests were adjusted: two invalid test lines that expected right-side simplification were removed and new valid cases were added (e.g. account?.test || false, boolExp || true, x && true, x && false). A changelog entry documents the fix (issue #8577).

Suggested reviewers

dyc3
ematipico

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarises the main change: preventing simplification of logic expressions with right-side boolean literals.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the fix for issue `#8577` and the reasoning behind removing right-side boolean literal simplifications.
Linked Issues check	✅ Passed	The code changes directly address `#8577` by removing the redundant simplification logic for right-side boolean literals in both OR and AND branches, with corresponding test updates.
Out of Scope Changes check	✅ Passed	All changes are in scope: the rule implementation fix, test updates validating the fix, and a changelog entry documenting the issue resolution.

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ematipico · 2026-02-05T18:45:26Z

@FrankFMY

In all three PRs you just did:

restore the PR template and fill it
READ the template. There are instructions for a changeset, which is mandatory
add AI disclosure as per requirements

FrankFMY · 2026-02-06T11:27:50Z

Sorry about that! I've updated all three PRs — added changesets, restored the PR template with all sections filled in, and included AI disclosure. Should be good now.

coderabbitai

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In @.changeset/use-simplified-logic-expression-false-positive.md:
- Line 5: Update the changelog sentence about `|| false` in the
`useSimplifiedLogicExpression` note to accurately describe its behavior: explain
that `x || false` preserves truthy values (returns the original truthy value,
e.g., `"hello" || false` → `"hello"`) and only coerces falsy values (including
`undefined`) to `false`, rather than performing full boolean coercion to
`true`/`false`; keep the existing example `account?.test || false` and the note
that right-side `|| false` is intentional boolean-coercion-for-falsy-values
while left-side simplifications (`true && x`, `false || x`) remain unchanged.

coderabbitai · 2026-02-06T11:29:09Z

.changeset/use-simplified-logic-expression-false-positive.md

+"@biomejs/biome": patch
+---
+
+Fixed [#8577](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` are intentional boolean coercion — `|| false` ensures the result is always `true` or `false` rather than potentially `undefined`. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics.


⚠️ Potential issue | 🟡 Minor

Clarify the behaviour of || false.

The description states that || false ensures the result is always true or false, but this isn't quite accurate. In JavaScript, x || false returns x unchanged if it's truthy (e.g., "hello" || false returns "hello", not true), and returns false only if x is falsy. The pattern preserves truthy values whilst coercing falsy values (including undefined) to false, rather than performing full boolean coercion.

📝 Suggested clarification

-Fixed [`#8577`](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` are intentional boolean coercion — `|| false` ensures the result is always `true` or `false` rather than potentially `undefined`. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics. +Fixed [`#8577`](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` intentionally coerce falsy values (including `undefined` and `null`) to `false` whilst preserving truthy values — removing `|| false` would change the expression's result. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics.

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

Fixed [#8577](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` are intentional boolean coercion — `|| false` ensures the result is always `true` or `false` rather than potentially `undefined`. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics.

Fixed [`#8577`](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` intentionally coerce falsy values (including `undefined` and `null`) to `false` whilst preserving truthy values — removing `|| false` would change the expression's result. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics.

🧰 Tools

🪛 LanguageTool

[formatting] ~5-~5: Did you mean “?”
Context: ...ral is on the right side. Patterns like account?.test || false are intentional boolean c...

(MULTIPLE_PUNCTATION_MARKS_1)

🤖 Prompt for AI Agents

In @.changeset/use-simplified-logic-expression-false-positive.md at line 5, Update the changelog sentence about `|| false` in the `useSimplifiedLogicExpression` note to accurately describe its behavior: explain that `x || false` preserves truthy values (returns the original truthy value, e.g., `"hello" || false` → `"hello"`) and only coerces falsy values (including `undefined`) to `false`, rather than performing full boolean coercion to `true`/`false`; keep the existing example `account?.test || false` and the note that right-side `|| false` is intentional boolean-coercion-for-falsy-values while left-side simplifications (`true && x`, `false || x`) remain unchanged.

codspeed-hq · 2026-02-06T11:40:27Z

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing FrankFMY:fix/use-simplified-logic-expression-false-positive (606e92c) with main (2cba2b3)¹}

Summary

✅ 58 untouched benchmarks
⏩ 95 skipped benchmarks²

No successful run was found on main (5a341b2) during the generation of this report, so 2cba2b3 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩
95 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

ematipico · 2026-02-06T12:03:17Z

.changeset/use-simplified-logic-expression-false-positive.md

+"@biomejs/biome": patch
+---
+
+Fixed [#8577](https://github.com/biomejs/biome/issues/8577): [`useSimplifiedLogicExpression`](https://biomejs.dev/linter/rules/use-simplified-logic-expression/) no longer suggests simplifying logical expressions when the boolean literal is on the right side. Patterns like `account?.test || false` are intentional boolean coercion — `|| false` ensures the result is always `true` or `false` rather than potentially `undefined`. Left-side simplifications (`true && x`, `false || x`) remain unchanged as they are always safe due to short-circuit semantics.


This changeset is an overkill. We can use a more human-like wording, simpler. Maybe just one code snippet is enough

FrankFMY · 2026-02-06T12:14:33Z

Simplified the changeset — just one sentence with one code snippet now.

github-actions bot added A-Linter Area: linter L-JavaScript Language: JavaScript and super languages labels Feb 5, 2026

chore: add changeset for useSimplifiedLogicExpression false positive fix

20d0a91

coderabbitai bot reviewed Feb 6, 2026

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ematipico reviewed Feb 6, 2026

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chore: simplify changeset wording

606e92c

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fix(linter): don't simplify logic expressions with right-side boolean literals#8976

fix(linter): don't simplify logic expressions with right-side boolean literals#8976
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