Bug 148780 – DOMTokenList.add() / remove() should run the update steps even if tokens were not modified

• Component: DOM
• Status: RESOLVED FIXED

[Ryosuke Niwa]

MutationObserver should be getting new records on classList.add/remove even if they're no-op.

See https://dom.spec.whatwg.org/#concept-DTL-update

Firefox adds the records as expected by the spec.

This bug was found by the newly added test: LayoutTests/http/tests/w3c/dom/nodes/MutationObserver-attributes.html

[Radar WebKit Bug Importer]

<rdar://problem/22571794>

[Chris Dumez]

Created attachment 261670 [details]
Patch

[Ryosuke Niwa]

Comment on attachment 261670 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=261670&action=review

> LayoutTests/fast/dom/rel-list.html:80
>      element.relList.add('x');
> -    shouldBeEqualToString('element.rel', 'x  x');
> +    shouldBeEqualToString('element.rel', 'x');

This seems like an orthogonal behavioral change.
This is expected?  If so, we should explain why this behavior change is desirable in the change log.

[Chris Dumez]

Comment on attachment 261670 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=261670&action=review

>> LayoutTests/fast/dom/rel-list.html:80
>> +    shouldBeEqualToString('element.rel', 'x');
> 
> This seems like an orthogonal behavioral change.
> This is expected?  If so, we should explain why this behavior change is desirable in the change log.

Not really an orthogonal change, as per the specification, we can the update steps even if the token update is a no-op. The update steps are:
https://dom.spec.whatwg.org/#concept-DTL-update

Step 2 is "Set an attribute value for the associated element using associated attribute’s local name and the result of running the ordered set serializer for tokens." Setting the attribute value will generate a mutation event but will also possible change the value as "ordered set serializer for tokens" will clean up the attribute value. I will update the change log to clarify before landing.

[Chris Dumez]

Created attachment 261680 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 261680 [details]
Patch

Clearing flags on attachment: 261680

Committed r190078: <http://trac.webkit.org/changeset/190078>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.