[cssom-view] scrollIntoView and shadow DOM

[zcorpan]

https://drafts.csswg.org/cssom-view/#element-scrolling-members

To scroll an element into view element, with a ScrollIntoViewOptions dictionary options, means to run these steps for each ancestor element or viewport that establishes a scrolling box scrolling box, in order of innermost to outermost scrolling box:​

How should element.scrollIntoView() interact with shadow DOM? cc @hayatoito @rniwa @TakayoshiKochi

[hayatoito]

Should we change ancestor with shadow-including-ancestor, as we did a similar thing for fullscreen api whatwg/fullscreen@611a404 ? I am not sure what is needed here. Someone who is familiar with scrollIntoView should think about which is needed.

[mihaiav]

It seems scrollIntoView is not working inside shadow dom(be it closed or open) which makes scrollIntoView and shadow dom are mutually exclusive. Is there any chance for this to be fixed anytime soon? I'm working on a project and the lack of support for scrollIntoView into shadow dom makes the UX quite bad.

[hayatoito]

@mihaiav

Do you know other browser's behavior about this? I think we all should fix this.
Blink's tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=918357

[rniwa]

element.scrollIntoView needs to run that step for each composed parent, not just shadow including ancestor because when an element is assigned to a slot, then its slot's scrollable ancestors need to scroll as well.