1040699 - Remove "group assignment" optimization in destructuring assignment

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Arpad Borsos [:Swatinem]]

From bug 933276 comment 21:

(In reply to Jason Orendorff [:jorendorff] from comment #21)
> Arpad, I just realized it's necessary to delete the "group assignment"
> optimization.
> 
> Try this and you'll see what I mean:
> 
> js> delete Array.prototype["@@iterator"];
> js> (function () { var [x, y] = [1, 2]; })() // should throw TypeError
> because Array#@@iterator is gone
> js> dis(function () { var [x, y] = [1, 2]; })
> 
> 
> Fortunately that should be very easy to delete. Please do it in a separate
> patch though, preferably *under* (before) this patch.

Right now, we have a special "group assignment" optimization that is triggered when we have an ArrayPattern on the LHS and an ArrayLiteral on the RHS.

Bug 933276 will move destructuring assignment over to use @@iterator, as specified in ES6, which collides with this optimization.
Removing it and always using the normal destructuring code should make moving to @@iterator a lot easier.

Comment 1

[Arpad Borsos [:Swatinem]]

Attachment: Remove "group assignment" optimization in destructuring assignment

Comment 2

[Jason Orendorff [:jorendorff]]

Comment on attachment 8459138 [details] [diff] [review]
Remove "group assignment" optimization in destructuring assignment

Review of attachment 8459138 [details] [diff] [review]:
-----------------------------------------------------------------

Thank you.

Comment 3

[Arpad Borsos [:Swatinem]]

http://hg.mozilla.org/integration/mozilla-inbound/rev/3b2046d81e35

Comment 4

[Ryan VanderMeulen (PTO, back July 27)]

https://hg.mozilla.org/mozilla-central/rev/3b2046d81e35