chakra-core/ChakraCore

[RegExp] Exceptions for RegExp in Annex B of the ES2017 spec shouldn't be applied when the "unicode" flag is present

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#518 opened on Mar 10, 2016

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BugSeverity: 2help wanted

Description

Annex B.1.4 contains exceptions that allow web browsers to diverge from the normal RegExp grammar. These exceptions aren't allowed when the "unicode" flag is present, but our current implementation doesn't take this into account.

There are many exceptions, but a few examples would be:

  • PatternCharacter: {
  • CharacterClassEscape: [\d-a]
  • DecimalEscape: \3 when the number of capturing parentheses is less than 3
  • IdentityEscape: \h, \u
  • QuantifiableAssertion Quantifier: (?!.)+

The above should throw a SyntaxError when used as, e.g.,/{/u

Contributor guide

Tech stack
javascript
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic understanding of regular expressionsfamiliarity with ChakraCore regex parser
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Start by examining the regex parsing code in ChakraCore, likely in the src/Regex or similar directory. The issue describes specific exceptions in Annex B.1.4 that should not apply when the 'unicode' flag is present. Look for where these exceptions are implemented and add a check for the unicode flag to throw SyntaxError. The examples given (e.g., `/{/u`) can be used as test cases. Note that the issue is from 2016, so the codebase may have evolved; check recent commits or comments for any partial fixes.