JS: Recognise that a less-than test is as good as a non-equal test for mitigating off-by-one array access #20423
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Pull Request Overview
This PR enhances the JavaScript off-by-one array access detection by recognizing that a less-than test (<) provides the same protection as a not-equal test (!=) when mitigating off-by-one errors in array bounds checking.
- Added a new
getLengthLTGuardfunction to detectindex < array.lengthconditions - Updated the main query logic to exclude cases where either a not-equal or less-than guard exists
- Added test case demonstrating the fix with
i < a.lengthguard
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| javascript/ql/src/LanguageFeatures/LengthComparisonOffByOne.ql | Added getLengthLTGuard function and updated query to consider less-than guards |
| javascript/ql/test/query-tests/LanguageFeatures/LengthComparisonOffByOne/tst.js | Added test case for function with less-than guard to verify the fix |
…tigating off-by-one array access
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asgerf
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Sep 15, 2025
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Drive-by fix noticed while looking through alleged bad autofixes (autofix used a
<test and CodeQL claimed it was an invalid fix)