Support Style Sharing for Shadow DOM V1

third_party/WebKit/Source/core/css/SelectorChecker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 96 matching lines @@
   //   (a) context.element has the same treescope as context.scope, need to walk
   //       up to its shadow host.
   //   (b) Otherwise, should not walk up from a shadow root to a shadow host.
   if (context.scope &&
       (context.scope == context.element->containingShadowRoot() ||
        context.scope->treeScope() == context.element->treeScope()))
     return context.element->parentOrShadowHostElement();
   return context.element->parentElement();
 }
 
+// If context has scope, return slot that matches the scope, otherwise return
+// the assigned slot for scope-less matching of ::slotted pseudo element.
 static const HTMLSlotElement* findSlotElementInScope(
     const SelectorChecker::SelectorCheckingContext& context) {
   if (!context.scope)
-    return nullptr;
+    return context.element->assignedSlot();

[rune, 2017/01/11 11:34:27]

Not sure I understand this one. This is fixing a known bug? Test?

[kochi, 2017/01/13 10:46:45]

ElemenetRuleCollector::hasAnyMatchingRules() does scope-less
checking for rules, and SharedStyleFinder uses it for
m_siblingRuleSet and m_uncommonAttributeRuleSet.

A "::slotted([attr])" style rule is put to m_uncommonAttributeRuleSet
but fails to match because of this scope checking.
Therefore such element that should match the rule fails to match,
and falsely shares style with some sibling if exists.

 
-  const HTMLSlotElement* slot = context.element->assignedSlot();
-  while (slot) {
+  for (const HTMLSlotElement* slot = context.element->assignedSlot(); slot;
+       slot = slot->assignedSlot()) {
     if (slot->treeScope() == context.scope->treeScope())
       return slot;
-    slot = slot->assignedSlot();
   }
   return nullptr;
 }
 
 static bool scopeContainsLastMatchedElement(
     const SelectorChecker::SelectorCheckingContext& context) {
   // If this context isn't scoped, skip checking.
   if (!context.scope)
     return true;
 
@@ skipping 1176 matching lines @@
 }
 
 bool SelectorChecker::matchesFocusPseudoClass(const Element& element) {
   if (InspectorInstrumentation::forcePseudoState(const_cast<Element*>(&element),
                                                  CSSSelector::PseudoFocus))
     return true;
   return element.isFocused() && isFrameFocused(element);
 }
 
 }  // namespace blink