694306 - Keywords should not be permitted in destructuring shorthand

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jason Orendorff [:jorendorff]]

js> var {if} = {if:1}; print(this.if);
1

I think this should be a SyntaxError rather than declare a variable named 'if'.

Comment 1

[Jason Orendorff [:jorendorff]]

In strict mode, we ban it, but the error message is odd.

  js> "use strict"; var {if} = {if: 1};
  typein:2: SyntaxError: redefining if is deprecated:

Comment 2

[Jason Orendorff [:jorendorff]]

Attachment: v1

Comment 3

[Jeff Walden [:Waldo]]

Comment on attachment 566885 [details] [diff] [review]
v1

Review of attachment 566885 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/jsscan.h
@@ +508,5 @@
> +     * and topp are null, report a SyntaxError ("if is a reserved identifier")
> +     * and return false. If ttp and topp are non-null, return true with the
> +     * keyword's TokenKind in *ttp and its JSOp in *topp.
> +     *
> +     * Preconditions:

Assert that these hold, please.

@@ +512,5 @@
> +     * Preconditions:
> +     *   s[length] must be valid to access and must not be an IdentifierPart.
> +     *   ttp and topp must be either both null or both non-null.
> +     */
> +    bool checkForKeyword(const jschar *s, size_t length, TokenKind *ttp, JSOp *topp);

These semantics are so hairy.  But maybe they're the cleanest ones.  :-\

Comment 4

[Jason Orendorff [:jorendorff]]

I'm dumb. FindKeyword never actually accesses s[length]. I don't know why I thought that. Because I didn't see explicit length checks scattered through jsautokw.h I guess; but because of the switch on length at the top, that isn't necessary.

So that's good. I removed the comment about that precondition, and added an assertion for the other precondition.

Comment 5

[Jason Orendorff [:jorendorff]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/50f566a3b449

Comment 6

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/50f566a3b449