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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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6
Libraries/LibWeb/CSS/StyleComputer.cpp
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@ -586,7 +586,11 @@ Vector<MatchingRule const*> StyleComputer::collect_matching_rules(DOM::Element c
auto const& selector = rule_to_run.selector;
SelectorEngine::MatchContext context { .style_sheet_for_rule = *rule_to_run.sheet };
SelectorEngine::MatchContext context {
.style_sheet_for_rule = *rule_to_run.sheet,
.subject = element,
.collect_per_element_selector_involvement_metadata = true,
};
ScopeGuard guard = [&] {
if (context.did_match_any_hover_rules)
did_match_any_hover_rules = true;