Cache element indices for :nth-child and :nth-last-child selectors.

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 110 matching lines @@
 class LayoutPoint;
 class LiveNodeListBase;
 class Locale;
 class LocalFrame;
 class Location;
 class MainThreadTaskRunner;
 class MediaQueryListListener;
 class MediaQueryMatcher;
 class NodeFilter;
 class NodeIterator;
+class NthIndexCache;
 class Page;
 class PlatformMouseEvent;
 class ProcessingInstruction;
 class QualifiedName;
 class Range;
 class LayoutView;
 class RequestAnimationFrameCallback;
 class ResourceFetcher;
 class SVGDocumentExtensions;
 class SVGUseElement;
@@ skipping 99 matching lines @@
     using ContainerNode::ref;
     using ContainerNode::deref;
 #endif
     using SecurityContext::securityOrigin;
     using SecurityContext::contentSecurityPolicy;
     using TreeScope::getElementById;
 
     virtual bool canContainRangeEndPoint() const override { return true; }
 
     SelectorQueryCache& selectorQueryCache();
+    NthIndexCache* nthIndexCache();
 
     // Focus Management.
     Element* activeElement() const;
     bool hasFocus() const;
 
     // DOM methods & attributes for Document
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(beforecopy);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(beforecut);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(beforepaste);
@@ skipping 794 matching lines @@
 
     void platformColorsChanged();
 
     virtual DOMTimerCoordinator* timers() override final;
 
     virtual v8::Handle<v8::Object> wrap(v8::Handle<v8::Object> creationContext, v8::Isolate*) override;
     virtual v8::Handle<v8::Object> associateWithWrapper(v8::Isolate*, const WrapperTypeInfo*, v8::Handle<v8::Object> wrapper) override;
 
     OriginsUsingFeatures::Value& originsUsingFeaturesValue() { return m_originsUsingFeaturesValue; }
 
+    class UseNthIndexCacheScope {
+        STACK_ALLOCATED();
+        WTF_MAKE_NONCOPYABLE(UseNthIndexCacheScope);
+    public:
+        UseNthIndexCacheScope(Document& document)
+            : m_document(&document)
+        {
+            ASSERT(!document.useNthIndexCache());

[sof, 2015/03/30 13:27:53]

Just to verify: there's no possibility that you may ever enter nested scopes?

[rune, 2015/03/30 20:14:40]

Shouldn't with the current uses of this scope. querySelector(All) should not
nest, and the DocumentLifecycle should ensure we don't nest updateStyle. The
assert here is to introduce future nesting problems. I'd rather avoid nested
scopes than mending them by checking/storing the current useNthIndexCache().

+            document.setUseNthIndexCache(true);
+        }
+        ~UseNthIndexCacheScope()
+        {
+            ASSERT(m_document->useNthIndexCache());
+            m_document->setUseNthIndexCache(false);
+        }
+    private:
+        RawPtrWillBeMember<Document> m_document;
+    };
+
 protected:
     Document(const DocumentInit&, DocumentClassFlags = DefaultDocumentClass);
 
     virtual void didUpdateSecurityOrigin() override final;
 
     void clearXMLVersion() { m_xmlVersion = String(); }
 
 #if !ENABLE(OILPAN)
     virtual void dispose() override;
 #endif
@@ skipping 236 matching lines @@
 
     OwnPtrWillBeMember<SVGDocumentExtensions> m_svgExtensions;
 
     Vector<AnnotatedRegionValue> m_annotatedRegions;
     bool m_hasAnnotatedRegions;
     bool m_annotatedRegionsDirty;
 
     WillBeHeapHashMap<String, RefPtrWillBeMember<HTMLCanvasElement>> m_cssCanvasElements;
 
     OwnPtr<SelectorQueryCache> m_selectorQueryCache;
+    OwnPtrWillBeMember<NthIndexCache> m_nthIndexCache;
 
     bool m_useSecureKeyboardEntryWhenActive;
 
     DocumentClassFlags m_documentClasses;
 
     bool m_isViewSource;
     bool m_sawElementsInKnownNamespaces;
     bool m_isSrcdocDocument;
     bool m_isMobileDocument;
     bool m_isTransitionDocument;
@@ skipping 60 matching lines @@
     bool m_hasViewportUnits;
 
     using DocumentVisibilityObserverSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<DocumentVisibilityObserver>>;
     DocumentVisibilityObserverSet m_visibilityObservers;
 
     int m_styleRecalcElementCounter;
 
     ParserSynchronizationPolicy m_parserSyncPolicy;
 
     OriginsUsingFeatures::Value m_originsUsingFeaturesValue;
+
+    bool useNthIndexCache() const { return m_useNthIndexCache; }
+    void setUseNthIndexCache(bool);
+
+    bool m_useNthIndexCache;
 };
 
 inline bool Document::shouldOverrideLegacyDescription(ViewportDescription::Type origin)
 {
     // The different (legacy) meta tags have different priorities based on the type
     // regardless of which order they appear in the DOM. The priority is given by the
     // ViewportDescription::Type enum.
     return origin >= m_legacyViewportDescription.type;
 }
 
@@ skipping 27 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h