Styling slot fallback content with ::slotted()

third_party/WebKit/Source/core/html/HTMLSlotElement.cpp

 /*
  * Copyright (C) 2015 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 33 matching lines @@
 #include "core/probe/CoreProbes.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 inline HTMLSlotElement::HTMLSlotElement(Document& document)
     : HTMLElement(slotTag, document) {
   UseCounter::Count(document, UseCounter::kHTMLSlotElement);
   SetHasCustomStyleCallbacks();
+  // TODO(kochi): This is required for slot fallback contents to be matched
+  // against ::slotted() pseudo element in a document tree. Remove this once
+  // Shadow DOM V0 code is removed.
+  document.SetShadowCascadeOrder(ShadowCascadeOrder::kShadowCascadeV1);
 }
 
 DEFINE_NODE_FACTORY(HTMLSlotElement);
 
 // static
 AtomicString HTMLSlotElement::NormalizeSlotName(const AtomicString& name) {
   return (name.IsNull() || name.IsEmpty()) ? g_empty_atom : name;
 }
 
+// static
+HTMLSlotElement* HTMLSlotElement::FindFallbackSlotElementFor(
+    const Element& element) {
+  // Check if |element| is a fallback content.
+  Element* parent = element.parentElement();
+  if (!parent || !isHTMLSlotElement(parent) ||
+      !toHTMLSlotElement(parent)->AssignedNodes().IsEmpty())
+    return nullptr;
+
+  // At this point, |parent| is an immediate parent of element, which is
+  // a <slot> with empty assigned nodes. This slot is one of the following:
+  // (1) doesn't have any slot in ancestor.
+  // (2) have a slot in ancestor which is assigned to another slot.
+  // (3) have a slot in ancestor which has assigned nodes.
+  // In cases (1) and (2), this slot is a fallback content.
+  // In case (3), this slot is not a fallback content.
+  HTMLSlotElement* slot = toHTMLSlotElement(parent);
+  while ((parent = parent->parentElement())) {
+    if (!isHTMLSlotElement(parent))
+      continue;
+    if (!toHTMLSlotElement(parent)->AssignedNodes().IsEmpty())
+      return nullptr;
+    slot = toHTMLSlotElement(parent);
+    if (slot->AssignedSlot())
+      break;
+  }
+  return slot;
+}
+
 const HeapVector<Member<Node>>& HTMLSlotElement::AssignedNodes() {
   DCHECK(!NeedsDistributionRecalc());
   DCHECK(IsInShadowTree() || assigned_nodes_.IsEmpty());
   return assigned_nodes_;
 }
 
 const HeapVector<Member<Node>> HTMLSlotElement::assignedNodesForBinding(
     const AssignedNodesOptions& options) {
   UpdateDistribution();
   if (options.hasFlatten() && options.flatten())
@@ skipping 289 matching lines @@
 
 DEFINE_TRACE(HTMLSlotElement) {
   visitor->Trace(assigned_nodes_);
   visitor->Trace(distributed_nodes_);
   visitor->Trace(old_distributed_nodes_);
   visitor->Trace(distributed_indices_);
   HTMLElement::Trace(visitor);
 }
 
 }  // namespace blink