Bug 140420 – JavaScript identifier incorrectly parsed if the prefix before an escape sequence is a keyword

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Alan Tam]

STEPS:
1. Run "in\u00e9dit = 1" in JavaScript console.

EXPECTED: It sets variable inédit to 1 and returns 1.
ACTUAL: SyntaxError: Unexpected keyword 'in'

This is a result of a minifier trying to convert all code to ASCII.

Chrome 39 and Firefox 34 both work fine.

[Michael Saboff]

This is probably related to adding for..in iteration to the parser.

[Michael Saboff]

Using ToT r178251.

For "in\u00e9dit = 1;" I get:
SyntaxError: Unexpected keyword 'in'

For "var in\u00e9dit = 1;" I get:
SyntaxError: Cannot use the keyword 'in' as a variable name.

[Alan Tam]

It is not limited to for..in, but all keywords. Indeed, object literal is another way to trigger the bug.

> ({while\u00e9dit:1})
SyntaxError: Unexpected identifier '\u00e9dit'. Expected a ':' following the property name 'while'.

Again, this works in Chrome and Firefox, returning this hash: {"whileédit":1}

[Michael Saboff]

Yes, it affects all keywords.

Test performance of a patch now.

[Michael Saboff]

The problem is due to parseKeyword() matching the "in" or any other keyword.  It then calls isIdentPart() on the next character, the \ for the unicode escape.  isIdentPart() only looks for characters with the types of CharacterIdentifierStart, CharacterZero and CharacterNumber.  The \ character is CharacterBackSlash.  The character that results from the unicode escape \u00e9 is é, which has the character class CharacterIdentifierStart.

parseKeyword() is generated from KeywordLookupGenerator.py.  Looks like it needs to be taught about escaped characters.

Adding a new isIdentPartOrEscape() function that will call isIdentPart().  If that fails, it looks for '\' an a valid unicode escape.  If it finds one, it checks that unicode character with isIdentPart().

[Michael Saboff]

Created attachment 244611 [details]
Patch

[Michael Saboff]

Created attachment 244612 [details]
Performance results of the patch

Seems to be neutral.

[Michael Saboff]

Committed r178427: <http://trac.webkit.org/changeset/178427>