417568 - Incorrect destructuring assignment

Status: RESOLVED INACTIVE

(Rhino Graveyard :: Compiler, defect)

Description

[Norris Boyd]

Steve Yegge wrote:

js> [[x, y].toSource() for ([x, y] in {foo: 'bar', hi: 'there'})]
["f", "o"],["h", "i"]

Seems like it ought to print:

["foo", "bar"], ["hi", "there"]

doesn't it?

Comment 1

[Steve Yegge]

It's also bugged for destructuring over an array:

js> [[x, y].toSource() for ([x, y] in [[1, 2], [3, 4], [5, 6]])]
["0", , ],["1", , ],["2", , ]

Comment 2

[Norris Boyd]

Attachment: 417568.doctest

Doctest for failure

Comment 3

[Hannes Wallnoefer]

Attachment: Fixes destructuring assignments in array comprehension

I changed array comprehension parsing to handle destructuring assignments in the same way ordinary for loops do. I guess I was lucky :-)

Comment 4

[Hannes Wallnoefer]

A few observations: 

With JavaScript 1.8, spidermonkey behaviour changes back to destructuring the key strings:

js> version(170)                                                  
180
js> [[x, y].toSource() for ([x, y] in {foo: 'bar', hi: 'there'})]
["foo", "bar"],["hi", "there"]
js> version(180)                                                  
170
js> [[x, y].toSource() for ([x, y] in {foo: 'bar', hi: 'there'})]
["f", "o"],["h", "i"]
js> 

Also see the last paragraph in the "what's new in js 1.8" page:
https://developer.mozilla.org/en/New_in_JavaScript_1.8#Changes_in_destructuring_for..in

I also noticed that my patch breaks test case js1_7/regress/regress-428706.js, complaining about more than 2 elements in the destructuring left hand side, which spidermonkey seems to accept if the third element is actually empty. Spidermonkey JS 1.8 seems to accept indefinite destructuring array elements, but only in ordinary loops, not array comprehension.  

IMO the question is whether array comprehension should follow the same rules as for loops. If the answer is yes, I think my patch is correct after all.

Comment 5

[Sylvestre Ledru [:Sylvestre]]

Closing. Bug management is now done here:
https://github.com/mozilla/rhino