1347706 - WindowProxy and Location [[SetPrototypeOf]] should not throw when null is passed

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

[Domenic Denicola]

WindowProxy and Location are supposed to behave as immutable prototype objects, and not allow changing their prototype. This behavior is supposed to be uniform across same- and cross-origin WindowProxy and Location objects.

- https://html.spec.whatwg.org/#windowproxy-setprototypeof
- https://html.spec.whatwg.org/#location-setprototypeof

The following web platform tests show that Firefox throws the wrong error in the cross-origin case:

- WindowProxy
  - http://w3c-test.org/html/browsers/the-windowproxy-exotic-object/windowproxy-prototype-setting-cross-origin-domain.sub.html
  - http://w3c-test.org/html/browsers/the-windowproxy-exotic-object/windowproxy-prototype-setting-cross-origin.sub.html
  - http://w3c-test.org/html/browsers/the-windowproxy-exotic-object/windowproxy-prototype-setting-goes-cross-origin-domain.sub.html
- Location
  - http://w3c-test.org/html/browsers/history/the-location-interface/location-prototype-setting-cross-origin-domain.sub.html
  - http://w3c-test.org/html/browsers/history/the-location-interface/location-prototype-setting-cross-origin.sub.html
  - http://w3c-test.org/html/browsers/history/the-location-interface/location-prototype-setting-goes-cross-origin-domain.sub.html

Firefox is doing fine though in general apart from the error types.

Comment 1

[Andrew Overholt [:overholt]]

Boris is probably the best person to know what's up here.

Comment 2

[Boris Zbarsky [:bzbarsky]]

A few things:

1)  Some of the tests are wrong.  Specifically, this:

    assert_throws(new TypeError, function() {
      target.__proto__ = newValue;
    });

is wrong.  If "target" is a cross-origin object, this lands in https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-set and thence in https://html.spec.whatwg.org/multipage/browsers.html#crossoriginset-(-o,-p,-v,-receiver-) which calls [[GetOwnProperty]] which throws a SecurityError DOMException in this case.  We never get to [[SetPrototypeOf]] at all in this case.  Domenic, do you mind fixing those tests?

2)  The "setting to null" behavior of not throwing is a very recent spec change.  I'm going to mutate this bug to cover that.

3)  The rest was fixed a week ago in bug 1344443.  ;)

Comment 3

[Boris Zbarsky [:bzbarsky]]

Attachment: Update to spec change for [[SetPrototypeOf]] on cross-origin objects. It should return true if null is passed

MozReview-Commit-ID: 42je5yfBRee

Comment 4

[Boris Zbarsky [:bzbarsky]]

Note that the wpt test at html/browsers/origin/cross-origin-objects/cross-origin-objects.html does the __proto__ thing right, by the way.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/38e85537c429
Update to spec change for [[SetPrototypeOf]] on cross-origin objects.  It should return true if null is passed.  r=bholley

Comment 6

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/38e85537c429