Bug 696205 part 2. Add a querySelector fast-path for selectors whose rightmost sequence of simple selectors contains an id. r=sicking

content/base/public/nsIDocument.h

@@ -126,8 +126,8 @@ class Element;
 } // namespace mozilla
 
 #define NS_IDOCUMENT_IID \
-{ 0x3d24831e, 0x2a2b, 0x42f4, \
-  { 0x9d, 0x98, 0x17, 0x60, 0x18, 0xab, 0x6e, 0xfb } }
+{ 0xb52356d4, 0xe191, 0x4cf8, \
+ { 0xb8, 0x58, 0xc0, 0xf1, 0xe1, 0x98, 0x09, 0xdf } }
 
 // Flag for AddStyleSheet().
 #define NS_STYLESHEET_FROM_CATALOG                (1 << 0)
@@ -1510,6 +1510,13 @@ public:
    */
   virtual Element* GetElementById(const nsAString& aElementId) = 0;
 
+  /**
+   * This method returns _all_ the elements in this document which
+   * have id aElementId, if there are any.  Otherwise it returns null.
+   * The entries of the nsSmallVoidArray are Element*
+   */
+  virtual const nsSmallVoidArray* GetAllElementsForId(const nsAString& aElementId) const = 0;
+
   /**
    * Lookup an image element using its associated ID, which is usually provided
    * by |-moz-element()|. Similar to GetElementById, with the difference that

content/base/src/nsDocument.cpp

@@ -4036,6 +4036,17 @@ nsDocument::GetElementById(const nsAString& aElementId)
   return entry ? entry->GetIdElement() : nsnull;
 }
 
+const nsSmallVoidArray*
+nsDocument::GetAllElementsForId(const nsAString& aElementId) const
+{
+  if (aElementId.IsEmpty()) {
+    return nsnull;
+  }
+
+  nsIdentifierMapEntry *entry = mIdentifierMap.GetEntry(aElementId);
+  return entry ? entry->GetIdElements() : nsnull;  
+}
+
 NS_IMETHODIMP
 nsDocument::GetElementById(const nsAString& aId, nsIDOMElement** aReturn)
 {

content/base/src/nsDocument.h

@@ -171,6 +171,12 @@ public:
    * id. Otherwise returns null.
    */
   Element* GetIdElement();
+  /**
+   * Returns the list of all elements associated with this id.
+   */
+  const nsSmallVoidArray* GetIdElements() const {
+    return &mIdContentList;
+  }
   /**
    * If this entry has a non-null image element set (using SetImageElement),
    * the image element will be returned, otherwise the same as GetIdElement().
@@ -244,7 +250,7 @@ private:
   void FireChangeCallbacks(Element* aOldElement, Element* aNewElement,
                            bool aImageOnly = false);
 
-  // empty if there are no elementswith this ID.
+  // empty if there are no elements with this ID.
   // The elements are stored as weak pointers.
   nsSmallVoidArray mIdContentList;
   nsRefPtr<nsBaseContentList> mNameContentList;
@@ -926,6 +932,7 @@ public:
                            const nsAString& aLocalName);
 
   virtual Element *GetElementById(const nsAString& aElementId);
+  virtual const nsSmallVoidArray* GetAllElementsForId(const nsAString& aElementId) const;
 
   virtual Element *LookupImageElement(const nsAString& aElementId);
 

content/base/src/nsGenericElement.cpp

@@ -5352,6 +5352,9 @@ ParseSelectorList(nsINode* aNode,
   return NS_OK;
 }
 
+// Actually find elements matching aSelectorList (which must not be
+// null) and which are descendants of aRoot and put them in Alist.  If
+// onlyFirstMatch, then stop once the first one is found.
 template<bool onlyFirstMatch, class T>
 inline static nsresult FindMatchingElements(nsINode* aRoot,
                                             const nsAString& aSelector,
@@ -5361,10 +5364,55 @@ inline static nsresult FindMatchingElements(nsINode* aRoot,
   nsresult rv = ParseSelectorList(aRoot, aSelector,
                                   getter_Transfers(selectorList));
   NS_ENSURE_SUCCESS(rv, rv);
+  NS_ENSURE_TRUE(selectorList, NS_OK);
+
+  NS_ASSERTION(selectorList->mSelectors,
+               "How can we not have any selectors?");
+
+  nsIDocument* doc = aRoot->OwnerDoc();  
+  TreeMatchContext matchingContext(false, nsRuleWalker::eRelevantLinkUnvisited,
+                                   doc);
+
+  // Fast-path selectors involving IDs.  We can only do this if aRoot
+  // is in the document and the document is not in quirks mode, since
+  // ID selectors are case-insensitive in quirks mode.  Also, only do
+  // this if selectorList only has one selector, because otherwise
+  // ordering the elements correctly is a pain.
+  NS_ASSERTION(aRoot->IsElement() || aRoot->IsNodeOfType(nsINode::eDOCUMENT),
+               "Unexpected root node");
+  if (aRoot->IsInDoc() &&
+      doc->GetCompatibilityMode() != eCompatibility_NavQuirks &&
+      !selectorList->mNext &&
+      selectorList->mSelectors->mIDList) {
+    nsIAtom* id = selectorList->mSelectors->mIDList->mAtom;
+    const nsSmallVoidArray* elements =
+      doc->GetAllElementsForId(nsDependentAtomString(id));
+
+    // XXXbz: Should we fall back to the tree walk if aRoot is not the
+    // document and |elements| is long, for some value of "long"?
+    if (elements) {
+      for (PRUint32 i = 0; i < elements->Count(); ++i) {
+        Element *element = static_cast<Element*>(elements->ElementAt(i));
+        if (!aRoot->IsElement() ||
+            nsContentUtils::ContentIsDescendantOf(element, aRoot)) {
+          // We have an element with the right id and it's a descendant
+          // of aRoot.  Make sure it really matches the selector.
+          if (nsCSSRuleProcessor::SelectorListMatches(element, matchingContext,
+                                                      selectorList)) {
+            aList.AppendElement(element);
+            if (onlyFirstMatch) {
+              return NS_OK;
+            }
+          }
+        }
+      }
+    }
+
+    // No elements with this id, or none of them are our descendants,
+    // or none of them match.  We're done here.
+    return NS_OK;
+  }
 
-  TreeMatchContext matchingContext(false,
-                                   nsRuleWalker::eRelevantLinkUnvisited,
-                                   aRoot->OwnerDoc());
   for (nsIContent* cur = aRoot->GetFirstChild();
        cur;
        cur = cur->GetNextNode(aRoot)) {