Bug 1249730 - make TreeWalker bi-directional, r=yzen

accessible/base/TreeWalker.cpp

@@ -58,8 +58,57 @@ TreeWalker::~TreeWalker()
   MOZ_COUNT_DTOR(TreeWalker);
 }
 
-////////////////////////////////////////////////////////////////////////////////
-// TreeWalker: private
+bool
+TreeWalker::Seek(nsIContent* aChildNode)
+{
+  MOZ_ASSERT(aChildNode, "Child cannot be null");
+
+  mPhase = eAtStart;
+  mStateStack.Clear();
+  mARIAOwnsIdx = 0;
+
+  nsIContent* childNode = nullptr;
+  nsINode* parentNode = aChildNode;
+  do {
+    childNode = parentNode->AsContent();
+    parentNode = childNode->HasFlag(NODE_MAY_BE_IN_BINDING_MNGR) &&
+      (mChildFilter & nsIContent::eAllButXBL) ?
+      childNode->GetParentNode() : childNode->GetFlattenedTreeParent();
+
+    if (!parentNode || !parentNode->IsElement()) {
+      return false;
+    }
+
+    // If ARIA owned child.
+    Accessible* child = mDoc->GetAccessible(childNode);
+    if (child && child->IsRelocated()) {
+      if (child->Parent() != mContext) {
+        return false;
+      }
+
+      Accessible* ownedChild = nullptr;
+      while ((ownedChild = mDoc->ARIAOwnedAt(mContext, mARIAOwnsIdx++)) &&
+             ownedChild != child);
+
+      MOZ_ASSERT(ownedChild, "A child has to be in ARIA owned elements");
+      mPhase = eAtARIAOwns;
+      return true;
+    }
+
+    // Look in DOM.
+    dom::AllChildrenIterator* iter = PrependState(parentNode->AsElement(), true);
+    if (!iter->Seek(childNode)) {
+      return false;
+    }
+
+    if (parentNode == mAnchorNode) {
+      mPhase = eAtDOM;
+      return true;
+    }
+  } while (true);
+
+  return false;
+}
 
 Accessible*
 TreeWalker::Next()

accessible/base/TreeWalker.h

@@ -49,6 +49,12 @@ public:
 
   ~TreeWalker();
 
+  /**
+   * Clears the tree walker state and resets it to the given child within
+   * the anchor.
+   */
+  bool Seek(nsIContent* aChildNode);
+
   /**
    * Return the next/prev accessible.
    *
@@ -59,13 +65,17 @@ public:
   Accessible* Next();
   Accessible* Prev();
 
+  Accessible* Context() const { return mContext; }
+  DocAccessible* Document() const { return mDoc; }
+
 private:
   TreeWalker();
   TreeWalker(const TreeWalker&);
   TreeWalker& operator =(const TreeWalker&);
 
   /**
-   * Create new state for the given node and push it on top of stack.
+   * Create new state for the given node and push it on top of stack / at bottom
+   * of stack.
    *
    * @note State stack is used to navigate up/down the DOM subtree during
    *        accessible children search.
@@ -76,6 +86,12 @@ private:
     return mStateStack.AppendElement(
       dom::AllChildrenIterator(aContent, mChildFilter, aStartAtBeginning));
   }
+  dom::AllChildrenIterator* PrependState(nsIContent* aContent,
+                                         bool aStartAtBeginning)
+  {
+    return mStateStack.InsertElementAt(0,
+      dom::AllChildrenIterator(aContent, mChildFilter, aStartAtBeginning));
+  }
 
   /**
    * Pop state from stack.