Implement 'mouseenter' and 'mouseleave' from DOM Level 3 Events.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 30687207b4c4beb57bae8b01403e1cd1678204e4..6b6900f01ed739fa3930116e1ccf7daa40b4ca44 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -2895,7 +2895,7 @@ MouseEventWithHitTestResults Document::prepareMouseEvent(const HitTestRequest& r
     renderView()->hitTest(request, result);
 
     if (!request.readOnly())
-        updateHoverActiveState(request, result.innerElement());
+        updateHoverActiveState(request, result.innerElement(), &event);
 
     return MouseEventWithHitTestResults(event, result);
 }
@@ -4990,13 +4990,13 @@ static RenderObject* nearestCommonHoverAncestor(RenderObject* obj1, RenderObject
     return 0;
 }
 
-void Document::updateHoverActiveState(const HitTestRequest& request, Element* innerElement)
+void Document::updateHoverActiveState(const HitTestRequest& request, Element* innerElement, const PlatformMouseEvent* event)
 {
     ASSERT(!request.readOnly());
 
     Element* innerElementInDocument = innerElement;
     while (innerElementInDocument && innerElementInDocument->document() != this) {
-        innerElementInDocument->document()->updateHoverActiveState(request, innerElementInDocument);
+        innerElementInDocument->document()->updateHoverActiveState(request, innerElementInDocument, event);
         innerElementInDocument = innerElementInDocument->document()->ownerElement();
     }
 
@@ -5059,6 +5059,28 @@ void Document::updateHoverActiveState(const HitTestRequest& request, Element* in
     Vector<RefPtr<Node>, 32> nodesToRemoveFromChain;
     Vector<RefPtr<Node>, 32> nodesToAddToChain;
 
+    // mouseenter and mouseleave events do not bubble, so they are dispatched iff there is a capturing

[PhistucK, 2013/07/08 17:57:26]

s/iff/if

[Mike West, 2013/07/09 09:37:00]

"iff" is short for "if and only if" (e.g. "necessary and sufficient"). I guess
that's not a well-known abbreviation. I'll change the text.

+    // event handler on an ancestor or a normal event handler on the element itself. This special
+    // handling is necessary to avoid O(n^2) capturing event handler checks.
+    bool hasCapturingMouseEnterListener = false;
+    bool hasCapturingMouseLeaveListener = false;
+    if (event && newHoverNode != oldHoverNode.get()) {
+        // Walk up the newly hovered node's ancestor tree for 'mouseenter' events, and the previously
+        // hovered node's ancestor tree for 'mouseleave' events.
+        for (Node* node = newHoverNode; node; node = node->parentOrShadowHostNode()) {
+            if (node->hasCapturingEventListeners(eventNames().mouseenterEvent)) {
+                hasCapturingMouseEnterListener = true;
+                break;
+            }
+        }
+        for (Node* node = oldHoverNode.get(); node; node = node->parentOrShadowHostNode()) {
+            if (node->hasCapturingEventListeners(eventNames().mouseleaveEvent)) {
+                hasCapturingMouseLeaveListener = true;
+                break;
+            }
+        }
+    }
+
     if (oldHoverObj != newHoverObj) {
         // If the old hovered node is not nil but it's renderer is, it was probably detached as part of the :hover style
         // (for instance by setting display:none in the :hover pseudo-class). In this case, the old hovered element (and its ancestors)
@@ -5085,8 +5107,11 @@ void Document::updateHoverActiveState(const HitTestRequest& request, Element* in
     }
 
     size_t removeCount = nodesToRemoveFromChain.size();
-    for (size_t i = 0; i < removeCount; ++i)
+    for (size_t i = 0; i < removeCount; ++i) {
         nodesToRemoveFromChain[i]->setHovered(false);
+        if (event && (hasCapturingMouseLeaveListener || nodesToRemoveFromChain[i]->hasEventListeners(eventNames().mouseleaveEvent)))
+            nodesToRemoveFromChain[i]->dispatchMouseEvent(*event, eventNames().mouseleaveEvent, 0, newHoverNode);
+    }
 
     bool sawCommonAncestor = false;
     size_t addCount = nodesToAddToChain.size();
@@ -5096,8 +5121,11 @@ void Document::updateHoverActiveState(const HitTestRequest& request, Element* in
             sawCommonAncestor = true;
         if (allowActiveChanges)
             nodesToAddToChain[i]->setActive(true);
-        if (!sawCommonAncestor)
+        if (!sawCommonAncestor) {
             nodesToAddToChain[i]->setHovered(true);
+            if (event && (hasCapturingMouseEnterListener || nodesToAddToChain[i]->hasEventListeners(eventNames().mouseenterEvent)))

[esprehn, 2013/07/08 18:13:02]

This is not correct, I could add a listener inside the mouseleave handler and
you'd not fire the event because you checked too early.

[Mike West, 2013/07/09 09:37:00]

You're right; I didn't think of that case at all. I'll split up the checks, and
add a new test to cover that behavior.

+                nodesToAddToChain[i]->dispatchMouseEvent(*event, eventNames().mouseenterEvent, 0, oldHoverNode.get());
+        }
     }
 
     updateStyleIfNeeded();