# biome complexity/useSimplifiedLogicExpression: fixed output does not parse Internal evidence sheet generated by fixhunt. Not an issue text. A human re-verifies, checks the duplicates below, and writes the upstream report in their own words following the project's AI policy. - Tool: biome 2.5.15 - Rule: complexity/useSimplifiedLogicExpression (tool labels the fix: safe, this fix reported as safe) - Oracle: fix-breaks-syntax - Judge (Nemotron 3 Ultra, advisory): real, severity high. The rule rewrites 'true && function() { return 1; }()' to 'function() { return 1; }()', but a function expression in statement position is a syntax error because function statements require a name. The original code was valid because the function expression was an operand of &&, making it an expression statement; the fix changes the parse context and breaks syntax. - Program: minimized from 6 to 4 lines ## Reproducer ```js try { true && function() { return 1; }(); } catch (e) { } ``` ## Commands ```sh node prog.js bunx @biomejs/biome lint --only=complexity/useSimplifiedLogicExpression --write prog.js node prog.js ``` ## Observed ``` /home/sun/dev/diaghunt/runs/2026-10-17T20-15-13-121Z-vjcv-biome-complexity_useSimplifiedLogicExpression/r2-p001/min/r2-p001-reuse/fixed.js:2 function() { return 1; }(); ^^^^^^^^ SyntaxError: Function statements require a function name at checkSyntax (node:internal/main/check_syntax:84:5) Node.js v26.8.1 ``` ## Diff applied by the fix ```diff --- orig.js 2026-10-22 13:26:40.370213262 -0400 +++ fixed.js 2026-10-22 13:26:42.425247346 -0400 @@ -1,4 +1,4 @@ try { - true && function() { return 1; }(); + function() { return 1; }(); } catch (e) { } ``` ## Why the rewrite is not equivalent (model draft, verify before use) The original expression `true && function(){return 1;}()` evaluates to either false or 1 depending on truthiness of left operand but always executes the IIFE due to grouping parentheses after function definition. After rewriting as just `function(){return 1;}();`, it becomes a bare function declaration followed by a call expression which JavaScript parses as invalid syntax—function declarations require an identifier—and thus throws before any execution occurs, changing behavior from potentially returning a value to unconditionally throwing a SyntaxError. This alters both control flow and outcome. ## Upstream search Queries: "useSimplifiedLogicExpression fix", "complexity useSimplifiedLogicExpression logical AND", "Biome rule simplify truthy expressions", "remove redundant true && in try block" - duplicate: https://github.com/biomejs/biome/issues/11351 same rule useSimplifiedLogicExpression removing a leading literal in a logical expression and breaking syntax - related: https://github.com/biomejs/biome/issues/7984 same rule useSimplifiedLogicExpression but different construct multiline conditions with comments - related: https://github.com/biomejs/biome/issues/8577 same rule useSimplifiedLogicExpression but different construct redundant terms in logical expression - related: https://github.com/biomejs/biome/issues/279 same rule useSimplifiedLogicExpression but different construct type narrowing with logical negation
All hits - [github, closed] 💅 `useSimplifiedLogicExpression` "safe" fix breaks code — https://github.com/biomejs/biome/issues/11351 - [github, open] 💅 `noUnnecessaryConditions`: false positive on an overloaded call with `undefined` as the default argument (Vue `inject`) — https://github.com/biomejs/biome/issues/12040 - [github, open] Extension chokes on large files — https://github.com/biomejs/biome/issues/3860 - [github, closed] 💅 `useExplicitLengthCheck` false positive and broken fix — https://github.com/biomejs/biome/issues/11558 - [github, closed] useExplicitLengthCheck ruins multi-line conditions that have single-line comments — https://github.com/biomejs/biome/issues/7984 - [github, closed] 💅 `useExplicitLengthCheck` false positive — https://github.com/biomejs/biome/issues/11352 - [github, closed] 💅 Corrupted CLI safe fix for `useConsistentArrowReturn` — https://github.com/biomejs/biome/issues/8347 - [github, closed] 💅 lint/nursery/noUselessUndefined fix is unsafe for functions with union return types — https://github.com/biomejs/biome/issues/6906 - [github, closed] 💅 `correctness/noUnusedVariables` shows class as unused, when `namespace` with the same name is present — https://github.com/biomejs/biome/issues/4928 - [github, closed] 💅 useImportExtensions doesn't respect tsconfig paths from referenced project configs — https://github.com/biomejs/biome/issues/7644 - [tavily] 💅 noNoninteractiveElementInteractions marks `dialog` as non-interactive · Issue #7783 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/7783 - [tavily] 💅 Incorrectly suggest to discard redundant terms (useSimplifiedLogicExpression) · Issue #8577 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/8577 - [tavily] One does not simply enable just one lint rule · Issue #1768 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/1768 - [tavily] 💅 useShorthandArrayType fix produces invalid syntax in `class extends` clause · Issue #3247 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/3247 - [tavily] 📝 CSS formatter messes up Tailwind theme(...) arguments · Issue #3863 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/3863 - [tavily] 🐛 OOM when using certain rules after 2.1.x · Issue #7179 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/7179 - [tavily] 📝 Sorting tailwind class with a calc is broken · Issue #5496 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/5496 - [tavily] 🐛 Typescript narrowing problem with `useSimplifiedLogicExpression` · Issue #279 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/279 - [tavily] ☂️ Tailwind class sorting lint rule · Issue #1274 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/1274 - [github, closed] 🐛 `noUnusedVariables` not looking at inner functions against a declared variable for a match — https://github.com/biomejs/biome/issues/105 - [github, closed] 🐛 `noUnusedVariables` misreporting imports used for type definitions — https://github.com/biomejs/biome/issues/104 - [tavily] 💅 lint/correctness/noUnusedVariables for `catch` clause should suggest removing variable definition as unsafe fix · Issue #6476 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/6476 - [tavily] 🐛panic when trying to fix 'Redundant use strict directive' - `crates\biome_js_formatter\src\utils\string_utils.rs:164:33` - `byte index 1 is out of bounds of` · Issue #9180 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/9180 - [tavily] 💅 Linter: `lint --write` is not idempotent on Astro frontmatter, while `lint` reports no issues · Issue #7912 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/7912 - [tavily] 💅 `useImportType` fixes `import React from 'react'` into `import type React from 'react'` · Issue #2004 · biomejs/biome · GitHub — https://github.com/biomejs/biome/issues/2004