Closed Bug 1448791 Opened 2 years ago Closed 2 years ago

[wpt-sync] Sync PR 10174 - Keep track of all pending slot assignments, and recalc all before UpdateStyle phase


(Core :: DOM: Core & HTML, enhancement, P4)




Tracking Status
firefox61 --- fixed


(Reporter: wptsync, Unassigned)




(Whiteboard: [wptsync downstream])

Sync web-platform-tests PR 10174 into mozilla-central (this bug is closed when the sync is complete).

Details from upstream follow.

Hayato Ito <> wrote:
>  Keep track of all pending slot assignments, and recalc all before UpdateStyle phase
>  For the purpose of rendering, Blink must calculate all pending slot assignments
>  before UpdateStyle phase. Unless that, a recursive RecalcStyle() may not
>  traverse a node which should be re-attached.
>  e.g. Suppose the following tree, where #d1 is assigned to a slot.
>  host
>  ├──/shadow-root
>  │   └── slot name=s1
>  └── div id=d1 slot=s1
>  Then, we change #d1's slot attribute to s2, like:
>  > document.querySelector('#d1').setAttribute('slot', 's2');
>  host
>  ├──/shadow-root
>  │   └── slot name=s1
>  └── div id=d1 slot=s2
>  In this case, #d1 should be removed from a LayoutTree. In other words, Blink
>  has to reattach #d1 somehow. However, if we don't recalc a slot assignment for
>  the shadow tree before UpdateStyle, a recursive RecalcStyle never traverses the
>  sub-tree because child-needs-style-recalc flag is not set for the node (and its
>  ancestor noes). A flag should be set as a result of slot assignment recalc.
>  Thanks to the Incremental Shadow DOM, a slot assignemt recalc now becomes a
>  local operatoin on each shadow tree, rather than one global operation for every
>  shadow trees. We don't need to traverse a composed tree to recalc all. We can
>  recalc a slot assignment for each shadow tree directly, without traversing a
>  composed tree.
>  For a shadow tree which is not connected, we don't need to recalc its slot
>  assignment before UpdateStyle because such a shadow tree shouldn't have any
>  effect on rendering. Lazy slot assignment recalc is enough for such a shadow
>  tree.
>  This CL doesn't introduce any optimization to minimize the number of
>  to-be-reattached nodes. I'll optimize that as a next task. I'll use a sort of
>  dynamic programming there, as I did at
> for
>  non-Incremental Shadow DOM.
>  Except for the performance, this CL should be the last part of Incremental
>  Shadow DOM from the external behavior's perspective. Style and Layout should
>  work correctly after this CL, even with Incremental Shadow DOM.
>  BUG=776656
>  Change-Id: Id18e87ff59d92863c68c571e7db09253c08aa91f
>  Reviewed-on:
>  WPT-Export-Revision: b186a1fe85672e9d484ea148d090c9e07c97c779
Component: web-platform-tests → DOM
Product: Testing → Core
P4 is unused to setting priority to P3.
Priority: P4 → P3
Priority: P3 → P4
Priority: P4 → P3
Priority: P3 → P4
Pushed by
[wpt PR 10174] - Keep track of all pending slot assignments, and recalc all before UpdateStyle phase, a=testonly
Closed: 2 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla61
Component: DOM → DOM: Core & HTML
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