[view-transitions] Resolving styles with a large set of named view-tr…

…ansition elements is slow.

https://bugs.webkit.org/show_bug.cgi?id=274739
<rdar://128774070>

Reviewed by Antti Koivisto.

For every named element in a view transition, 4 styles are inserted in the UA style sheet.

View transitions currently restyle the entire view transition pseudo tree for changes to any of
them (since mutations are keyed to the owning element, which is the document element for the whole tree).

There are 4 named pseudo elements per view transition name, resulting in pretty slow O(n^2) restyling.

We can improve this somewhat by putting pseudo element selectors with a name argument (like
::view-transition-group(name)) into a hash map, so that we only need to iterate the somewhat-relevant ones.

* Source/WebCore/style/ElementRuleCollector.cpp:
(WebCore::Style::ElementRuleCollector::collectMatchingRules):
* Source/WebCore/style/RuleSet.cpp:
(WebCore::Style::RuleSet::addRule):
(WebCore::Style::RuleSet::traverseRuleDatas):
(WebCore::Style::RuleSet::shrinkToFit):
* Source/WebCore/style/RuleSet.h:
(WebCore::Style::RuleSet::namedPseudoElementRules const):

Canonical link: https://commits.webkit.org/279484@main

Source/WebCore/style/ElementRuleCollector.cpp

@@ -219,6 +219,8 @@ void ElementRuleCollector::collectMatchingRules(const MatchRequest& matchRequest
         for (auto* rules : ruleVectors)
             collectMatchingRulesForList(rules, matchRequest);
     }
+    if (m_pseudoElementRequest && m_pseudoElementRequest->nameArgument() != nullAtom())
+        collectMatchingRulesForList(matchRequest.ruleSet.namedPseudoElementRules(m_pseudoElementRequest->nameArgument()), matchRequest);
     if (element.isLink())
         collectMatchingRulesForList(matchRequest.ruleSet.linkPseudoClassRules(), matchRequest);
     if (matchesFocusPseudoClass(element))

Source/WebCore/style/RuleSet.cpp

@@ -150,6 +150,7 @@ void RuleSet::addRule(RuleData&& ruleData, CascadeLayerIdentifier cascadeLayerId
     const CSSSelector* customPseudoElementSelector = nullptr;
     const CSSSelector* slottedPseudoElementSelector = nullptr;
     const CSSSelector* partPseudoElementSelector = nullptr;
+    const CSSSelector* namedPseudoElementSelector = nullptr;
 #if ENABLE(VIDEO)
     const CSSSelector* cuePseudoElementSelector = nullptr;
 #endif
@@ -204,6 +205,13 @@ void RuleSet::addRule(RuleData&& ruleData, CascadeLayerIdentifier cascadeLayerId
                 cuePseudoElementSelector = selector;
                 break;
 #endif
+            case CSSSelector::PseudoElement::ViewTransitionGroup:
+            case CSSSelector::PseudoElement::ViewTransitionImagePair:
+            case CSSSelector::PseudoElement::ViewTransitionOld:
+            case CSSSelector::PseudoElement::ViewTransitionNew:
+                if (selector->argumentList()->first().identifier != starAtom())
+                    namedPseudoElementSelector = selector;
+                break;
             default:
                 break;
             }
@@ -312,6 +320,11 @@ void RuleSet::addRule(RuleData&& ruleData, CascadeLayerIdentifier cascadeLayerId
         return;
     }
 
+    if (namedPseudoElementSelector) {
+        addToRuleSet(namedPseudoElementSelector->argumentList()->first().identifier, m_namedPseudoElementRules, ruleData);
+        return;
+    }
+
     if (rootElementSelector) {
         m_rootElementRules.append(ruleData);
         return;
@@ -352,6 +365,7 @@ void RuleSet::traverseRuleDatas(Function&& function)
     traverseMap(m_tagLocalNameRules);
     traverseMap(m_tagLowercaseLocalNameRules);
     traverseMap(m_userAgentPartRules);
+    traverseMap(m_namedPseudoElementRules);
     traverseVector(m_linkPseudoClassRules);
 #if ENABLE(VIDEO)
     traverseVector(m_cuePseudoRules);
@@ -445,6 +459,7 @@ void RuleSet::shrinkToFit()
     shrinkMapVectorsToFit(m_tagLocalNameRules);
     shrinkMapVectorsToFit(m_tagLowercaseLocalNameRules);
     shrinkMapVectorsToFit(m_userAgentPartRules);
+    shrinkMapVectorsToFit(m_namedPseudoElementRules);
 
     m_linkPseudoClassRules.shrinkToFit();
 #if ENABLE(VIDEO)

Source/WebCore/style/RuleSet.h

@@ -94,6 +94,7 @@ class RuleSet : public RefCounted<RuleSet> {
     const RuleDataVector* tagRules(const AtomString& key, bool isHTMLName) const;
     const RuleDataVector* userAgentPartRules(const AtomString& key) const { return m_userAgentPartRules.get(key); }
     const RuleDataVector* linkPseudoClassRules() const { return &m_linkPseudoClassRules; }
+    const RuleDataVector* namedPseudoElementRules(const AtomString& key) const { return m_namedPseudoElementRules.get(key); }
 #if ENABLE(VIDEO)
     const RuleDataVector& cuePseudoRules() const { return m_cuePseudoRules; }
 #endif
@@ -190,6 +191,7 @@ class RuleSet : public RefCounted<RuleSet> {
     AtomRuleMap m_tagLocalNameRules;
     AtomRuleMap m_tagLowercaseLocalNameRules;
     AtomRuleMap m_userAgentPartRules;
+    AtomRuleMap m_namedPseudoElementRules;
     RuleDataVector m_linkPseudoClassRules;
 #if ENABLE(VIDEO)
     RuleDataVector m_cuePseudoRules;