Allow positional selectors to match elements without a parent.

third_party/WebKit/Source/core/dom/NthIndexCache.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/NthIndexCache.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ElementTraversal.h"
 
 namespace blink {
@@ skipping 61 matching lines @@
     if (sibling->tagQName() == tag)
       ++index;
     ++siblingCount;
   }
   return index;
 }
 
 }  // namespace
 
 unsigned NthIndexCache::nthChildIndex(Element& element) {
-  if (element.isPseudoElement())
+  if (element.isPseudoElement() || !element.parentNode())
     return 1;
-  DCHECK(element.parentNode());
   NthIndexCache* nthIndexCache = element.document().nthIndexCache();
   NthIndexData* nthIndexData = nullptr;
   if (nthIndexCache && nthIndexCache->m_parentMap)
     nthIndexData = nthIndexCache->m_parentMap->get(element.parentNode());
   if (nthIndexData)
     return nthIndexData->nthIndex(element);
   unsigned index = uncachedNthChildIndex(element);
-  if (nthIndexCache && index > kCachedSiblingCountLimit)
+  if (element.parentNode() && nthIndexCache && index > kCachedSiblingCountLimit)

[rune, 2017/01/18 21:33:19]

parentNode() is always non-null here.

[emilio, 2017/01/18 23:33:07]

Good catches, sorry, should've paged in better all the conversation and the
previous review before updating the patch. You shouldn't have needed to point
these out.

     nthIndexCache->cacheNthIndexDataForParent(element);
   return index;
 }
 
 unsigned NthIndexCache::nthLastChildIndex(Element& element) {
   if (element.isPseudoElement())
     return 1;
-  DCHECK(element.parentNode());
   NthIndexCache* nthIndexCache = element.document().nthIndexCache();
   NthIndexData* nthIndexData = nullptr;
-  if (nthIndexCache && nthIndexCache->m_parentMap)
+  if (element.parentNode() && nthIndexCache && nthIndexCache->m_parentMap)

[rune, 2017/01/18 21:33:19]

Check !parentNode and return 1 as for nthChildIndex and skip the null check
here?

     nthIndexData = nthIndexCache->m_parentMap->get(element.parentNode());
   if (nthIndexData)
     return nthIndexData->nthLastIndex(element);
   unsigned index = uncachedNthLastChildIndex(element);
-  if (nthIndexCache && index > kCachedSiblingCountLimit)
+  if (element.parentNode() && nthIndexCache && index > kCachedSiblingCountLimit)

[rune, 2017/01/18 21:33:19]

No need to add the parentNode() check if you early-return 1 for !parentNode().

     nthIndexCache->cacheNthIndexDataForParent(element);
   return index;
 }
 
 NthIndexData* NthIndexCache::nthTypeIndexDataForParent(Element& element) const {
-  DCHECK(element.parentNode());
-  if (!m_parentMapForType)
+  if (!m_parentMapForType || !element.parentNode())

[rune, 2017/01/18 21:33:19]

Early return in nthOfTypeIndex and nthLastOfTypeIndex instead?

     return nullptr;
   if (const IndexByType* map = m_parentMapForType->get(element.parentNode()))
     return map->get(element.tagName());
   return nullptr;
 }
 
 unsigned NthIndexCache::nthOfTypeIndex(Element& element) {
   if (element.isPseudoElement())
     return 1;
   NthIndexCache* nthIndexCache = element.document().nthIndexCache();
@@ skipping 130 matching lines @@
   }
   DCHECK(count);
   m_count = count;
 }
 
 DEFINE_TRACE(NthIndexData) {
   visitor->trace(m_elementIndexMap);
 }
 
 }  // namespace blink