Bug 303414 – Container query interleaving prevents StyleAdjuster from running on top layer elements

• Status: NEW
• Component: New Bugs

[Ruthvik Konda]

When an element enters the top layer via fullscreen and its parent has container-type set, TreeResolver's container query interleaving logic (StyleTreeResolver.cpp:1382-1403) returns LayoutInterleavingAction::SkipDescendants, which defers style resolution for all descendants. This prevents StyleAdjuster::adjust() (StyleAdjuster.cpp:546-549) from ever running on the top layer element, so it never receives the required position:absolute style. This creates a broken invariant where the element remains in the normal flow of its layout parent (making isGridItem() return true) while containingBlock() correctly returns RenderView per top layer rules (RenderObject.cpp:782-783), leading to type confusion crashes. The fundamental issue is that style resolution interleaving breaks the contract that all top layer elements must be position:absolute. As a result, this architectural problem caused a downcast crash in rdar://163028025. If the top layer element was correctly set to position:absolute, then it would have correctly been out of flow positioned and the crash would've been avoided. Instead isGridItem() returns true and containingBlock() returns a RenderView which is fundamentally wrong.

rdar://163028025 has a workaround fix in place. But this is a deeper rooted issue that needs to go to a fullscreen or style resolution expert to solve.

[Radar WebKit Bug Importer]

<rdar://problem/165714112>