Handle fallback content case in FlatTreeTraversal::traverseSiblings()

third_party/WebKit/Source/core/dom/shadow/FlatTreeTraversal.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 116 matching lines @@
 
   if (shadowWhereNodeCanBeDistributedForV0(node))
     return traverseSiblingsForV0Distribution(node, direction);
 
   if (Node* found = resolveDistributionStartingAt(
           direction == TraversalDirectionForward ? node.nextSibling()
                                                  : node.previousSibling(),
           direction))
     return found;
 
+  if (node.isInV1ShadowTree()) {

[hayato, 2017/03/16 09:32:56]

Instead of this early check, could you use slot.suppportDistribution() to judge
the slot is *active* or not?
It is more consistent, and more robust for a future change.

[kochi, 2017/03/16 10:09:54]

Done.
Actually it looks better now.  Thanks for the suggestion.

+    // Slotted nodes are already handled in traverseSiblingsForV1HostChild()
+    // above, here is for fallback contents.
+    Element* parent = node.parentElement();
+    if (parent && isHTMLSlotElement(parent)) {
+      HTMLSlotElement& slot = toHTMLSlotElement(*parent);
+      if (!slot.assignedNodes().isEmpty())
+        return nullptr;
+      return traverseSiblings(slot, direction);
+    }
+  }
+
   if (!node.isInV0ShadowTree())
     return nullptr;
 
   // For v0 older shadow tree
   if (node.parentNode() && node.parentNode()->isShadowRoot()) {
     ShadowRoot* parentShadowRoot = toShadowRoot(node.parentNode());
     if (!parentShadowRoot->isYoungest()) {
       HTMLShadowElement* assignedInsertionPoint =
           parentShadowRoot->shadowInsertionPointOfYoungerShadowRoot();
       DCHECK(assignedInsertionPoint);
@@ skipping 236 matching lines @@
 
 Node& FlatTreeTraversal::lastWithinOrSelf(const Node& node) {
   assertPrecondition(node);
   Node* lastDescendant = lastWithin(node);
   Node& result = lastDescendant ? *lastDescendant : const_cast<Node&>(node);
   assertPostcondition(&result);
   return result;
 }
 
 }  // namespace blink