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LibWeb: Use invalidation sets for :has() invalidation

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Prior to this change, we invalidated all elements in the document if it
used any selectors with :has(). This change aims to improve that by
applying a combination of techniques:
- Collect metadata for each element if it was matched against a selector
  with :has() in the subject position. This is needed to invalidate all
  elements that could be affected by selectors like `div:has(.a:empty)`
  because they are not covered by the invalidation sets.
- Use invalidation sets to invalidate elements that are affected by
  selectors with :has() in a non-subject position.

Selectors like `.a:has(.b) + .c` still cause whole-document invalidation
because invalidation sets cover only descendants, not siblings. As a
result, there is no performance improvement on github.com due to this
limitation. However, youtube.com and discord.com benefit from this
change.
This commit is contained in:
Aliaksandr Kalenik 2025-01-29 03:31:46 +01:00 • committed by Andreas Kling
commit d762d16938
Notes: github-actions[bot] 2025-01-29 08:31:17 +00:00
8 changed files with 56 additions and 9 deletions
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3
Libraries/LibWeb/CSS/SelectorEngine.cpp
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@ -549,6 +549,9 @@ static inline bool matches_pseudo_class(CSS::Selector::SimpleSelector::PseudoCla
// :has() cannot be nested in a :has()
if (selector_kind == SelectorKind::Relative)
return false;
if (context.collect_per_element_selector_involvement_metadata && &element == context.subject) {
const_cast<DOM::Element&>(element).set_affected_by_has_pseudo_class_in_subject_position(true);
}
// These selectors should be relative selectors (https://drafts.csswg.org/selectors-4/#relative-selector)
for (auto& selector : pseudo_class.argument_selector_list) {
if (matches_has_pseudo_class(selector, element, shadow_host, context))