Andreas Kling 223ca14abc LibWeb: Support :host::part() selectors within shadow DOM stylesheets ...

The :host::part() pattern allows a shadow DOM's own stylesheet to
style its internal elements that have been exposed via the part
attribute. Previously, ::part() rules were only collected from
ancestor shadow roots (for external part styling), but never from the
element's own containing shadow root.

Fix this by also collecting ::part() rules from the element's own
shadow root in collect_matching_rules(). Additionally, fix the
selector engine's ::part() compound matching to preserve the
shadow_host when the rule originates from the part element's own
shadow root, allowing :host to match correctly in the same compound
selector.

This fixes 2 previously failing WPT tests:
- css/css-shadow-parts/host-part-002.html
- css/css-shadow-parts/host-part-nesting.html

2026-03-21 21:42:44 -05:00

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