[webkit-changes] [WebKit/WebKit] eb40da: Crash in collectStationaryLayerRelatedOverflowNodes()

[Simon Fraser]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: eb40daa6cd5006e841097c57d07d83e5dda55088
      https://github.com/WebKit/WebKit/commit/eb40daa6cd5006e841097c57d07d83e5dda55088
  Author: Simon Fraser <simon.fraser at apple.com>
  Date:   2023-04-22 (Sat, 22 Apr 2023)

  Changed paths:
    A LayoutTests/compositing/overflow/overflow-change-abspos-descendant-expected.txt
    A LayoutTests/compositing/overflow/overflow-change-abspos-descendant.html
    M Source/WebCore/rendering/RenderLayer.cpp

  Log Message:
  -----------
  Crash in collectStationaryLayerRelatedOverflowNodes()
https://bugs.webkit.org/show_bug.cgi?id=255830
<rdar://107526702>

Reviewed by Alan Baradlay.

Some unusual content configurations can hit the ASSERT(overflowLayer.isComposited())
in collectStationaryLayerRelatedOverflowNodes(), which ends up in a null dereference in release builds.

The issue occurs when a RenderLayer which was using composited scrolling becomes non-scrollable,
but hasCompositedScrollableOverflow() continues to return true, leading to errors in compositing code
which relies on canUseCompositedScrolling(). RenderLayerScrollableArea caches m_hasCompositedScrollableOverflow,
and failed to recompute it in this case.

Fix by having RenderLayer::styleChanged() force hasCompositedScrollableOverflow() to be recomputed
when style scrollability changes.

The testcase is derived from rdar://88329753.

* LayoutTests/compositing/overflow/overflow-change-abspos-descendant-expected.txt: Added.
* LayoutTests/compositing/overflow/overflow-change-abspos-descendant.html: Added.
* Source/WebCore/rendering/RenderLayer.cpp:
(WebCore::RenderLayer::calculateClipRects const):

Canonical link: https://commits.webkit.org/263286@main