Bug 1321284 - Crash in nsCSSFrameConstructor::GetInsertionPrevSibling when trying to reframe native anonymous content

* Make StyleChildrenIterator skip NAC generated by root element primary frame ancestors.
* Add nsINode::GetFlattenedTreeParentNodeForStyle.
* Add iterator class to find all restyle roots.

NOTE: Parts 1, 2, and "4.2"

Tag #1375

dom/base/ChildIterator.cpp

@@ -383,12 +383,10 @@ AllChildrenIterator::AppendNativeAnonymousChildren()
 
   // The root scroll frame is not the primary frame of the root element.
   // Detect and handle this case.
-  if (mOriginalContent == mOriginalContent->OwnerDoc()->GetRootElement()) {
-    nsIPresShell* presShell = mOriginalContent->OwnerDoc()->GetShell();
-    nsIFrame* scrollFrame = presShell ? presShell->GetRootScrollFrame() : nullptr;
-    if (scrollFrame) {
-      AppendNativeAnonymousChildrenFromFrame(scrollFrame);
-    }
+  if (!(mFlags & nsIContent::eSkipDocumentLevelNativeAnonymousContent) &&
+      mOriginalContent == mOriginalContent->OwnerDoc()->GetRootElement()) {
+    nsContentUtils::AppendDocumentLevelNativeAnonymousContentTo(
+        mOriginalContent->OwnerDoc(), mAnonKids);
   }
 }
 
@@ -585,12 +583,6 @@ StyleChildrenIterator::IsNeeded(const Element* aElement)
     return true;
   }
 
-  // The root element has a scroll frame that is not the primary frame, so we
-  // need to do special checking for that case.
-  if (aElement == aElement->OwnerDoc()->GetRootElement()) {
-    return true;
-  }
-
   return false;
 }
 

dom/base/ChildIterator.h

@@ -256,10 +256,11 @@ private:
 /**
  * StyleChildrenIterator traverses the children of the element from the
  * perspective of the style system, particularly the children we need to traverse
- * during restyle. This is identical to AllChildrenIterator with eAllChildren,
- * _except_ that we detect and skip any native anonymous children that are used
- * to implement pseudo-elements (since the style system needs to cascade those
- * using different algorithms).
+ * during restyle. This is identical to AllChildrenIterator with
+ * (eAllChildren | eSkipDocumentLevelNativeAnonymousContent), _except_ that we
+ * detect and skip any native anonymous children that are used to implement
+ * pseudo-elements (since the style system needs to cascade those using
+ * different algorithms).
  *
  * Note: it assumes that no mutation of the DOM or frame tree takes place during
  * iteration, and will break horribly if that is not true.
@@ -267,7 +268,9 @@ private:
 class StyleChildrenIterator : private AllChildrenIterator {
 public:
   explicit StyleChildrenIterator(const nsIContent* aContent)
-    : AllChildrenIterator(aContent, nsIContent::eAllChildren)
+    : AllChildrenIterator(aContent,
+                          nsIContent::eAllChildren |
+                          nsIContent::eSkipDocumentLevelNativeAnonymousContent)
   {
     MOZ_COUNT_CTOR(StyleChildrenIterator);
   }

dom/base/Element.h

@@ -390,6 +390,8 @@ public:
 
   Directionality GetComputedDirectionality() const;
 
+  inline Element* GetFlattenedTreeParentElementForStyle() const;
+
   /**
    * Gets the custom element data used by web components custom element.
    * Custom element data is created at the first attempt to enqueue a callback.

dom/base/ElementInlines.h

@@ -25,6 +25,17 @@ Element::UnregisterActivityObserver()
   OwnerDoc()->UnregisterActivityObserver(this);
 }
 
+inline Element*
+Element::GetFlattenedTreeParentElementForStyle() const
+{
+  nsINode* parentNode = GetFlattenedTreeParentNodeForStyle();
+  if MOZ_LIKELY(parentNode && parentNode->IsElement()) {
+    return parentNode->AsElement();
+  }
+
+  return nullptr;
+}
+
 } // namespace dom
 } // namespace mozilla
 

dom/base/FragmentOrElement.cpp

@@ -152,7 +152,7 @@ nsIContent::FindFirstNonChromeOnlyAccessContent() const
 }
 
 nsINode*
-nsIContent::GetFlattenedTreeParentNodeInternal() const
+nsIContent::GetFlattenedTreeParentNodeInternal(FlattenedParentType aType) const
 {
   nsINode* parentNode = GetParentNode();
   if (!parentNode || !parentNode->IsContent()) {
@@ -161,6 +161,45 @@ nsIContent::GetFlattenedTreeParentNodeInternal() const
   }
   nsIContent* parent = parentNode->AsContent();
 
+  if (aType == eForStyle &&
+      IsRootOfNativeAnonymousSubtree() &&
+      OwnerDoc()->GetRootElement() == parent) {
+    // When getting the flattened tree parent for style, we return null
+    // for any "document level" native anonymous content subtree root.
+    // This is NAC generated by an ancestor frame of the document element's
+    // primary frame, and includes scrollbar elements created by the root
+    // scroll frame, and the "custom content container" and accessible caret
+    // generated by the nsCanvasFrame.  We distinguish document level NAC
+    // from NAC generated by the root element's primary frame below.
+    nsIFrame* parentFrame = parent->GetPrimaryFrame();
+    if (!parentFrame) {
+      // If the root element has no primary frame, it means it can't have
+      // generated any NAC itself.  Thus any NAC we have here must have
+      // been generated by an ancestor frame.
+      //
+      // If we are in here, then either the root element is display:none, or
+      // we are in the middle of constructing the root of the frame tree and
+      // we are trying to eagerly restyle document level NAC in
+      // nsCSSFrameConstructor::GetAnonymousContent before the root
+      // element's frame has been constructed.
+      return nullptr;
+    }
+    nsIAnonymousContentCreator* creator = do_QueryFrame(parentFrame);
+    if (!creator) {
+      // If the root element does have a frame, but does not implement
+      // nsIAnonymousContentCreator, then this must be document level NAC.
+      return nullptr;
+    }
+    AutoTArray<nsIContent*, 8> elements;
+    creator->AppendAnonymousContentTo(elements, 0);
+    if (!elements.Contains(this)) {
+      // If the root element does have a frame, and also does implement
+      // nsIAnonymousContentCreator, but didn't create this node, then
+      // it must be document level NAC.
+      return nullptr;
+    }
+  }
+
   if (parent && nsContentUtils::HasDistributedChildren(parent) &&
       nsContentUtils::IsInSameAnonymousTree(parent, this)) {
     // This node is distributed to insertion points, thus we

dom/base/nsContentUtils.cpp

@@ -103,6 +103,7 @@
 #include "nsHtml5Module.h"
 #include "nsHtml5StringParser.h"
 #include "nsIAddonPolicyService.h"
+#include "nsIAnonymousContentCreator.h"
 #include "nsIAsyncVerifyRedirectCallback.h"
 #include "nsICategoryManager.h"
 #include "nsIChannelEventSink.h"
@@ -9837,6 +9838,24 @@ nsContentUtils::AttemptLargeAllocationLoad(nsIHttpChannel* aChannel)
   return reloadSucceeded;
 }
 
+/* static */ void
+nsContentUtils::AppendDocumentLevelNativeAnonymousContentTo(
+    nsIDocument* aDocument,
+    nsTArray<nsIContent*>& aElements)
+{
+  MOZ_ASSERT(aDocument);
+
+  // XXXheycam This probably needs to find the nsCanvasFrame's NAC too.
+  if (nsIPresShell* presShell = aDocument->GetShell()) {
+    if (nsIFrame* scrollFrame = presShell->GetRootScrollFrame()) {
+      nsIAnonymousContentCreator* creator = do_QueryFrame(scrollFrame);
+      MOZ_ASSERT(creator,
+                 "scroll frame should always implement nsIAnonymousContentCreator");
+      creator->AppendAnonymousContentTo(aElements, 0);
+    }
+  }
+}
+
 /* static */ bool
 nsContentUtils::IsLocalRefURL(const nsString& aString)
 {

dom/base/nsContentUtils.h

@@ -2742,6 +2742,16 @@ public:
 
   static bool AttemptLargeAllocationLoad(nsIHttpChannel* aChannel);
 
+  /**
+   * Appends all "document level" native anonymous content subtree roots for
+   * aDocument to aElements.  Document level NAC subtrees are those created
+   * by ancestor frames of the document element's primary frame, such as
+   * the scrollbar elements created by the root scroll frame.
+   */
+  static void AppendDocumentLevelNativeAnonymousContentTo(
+      nsIDocument* aDocument,
+      nsTArray<nsIContent*>& aElements);
+
   /**
    * Detect whether a string is a (CSS) local-url.
    * https://drafts.csswg.org/css-values/#local-urls

dom/base/nsIContent.h

@@ -144,7 +144,14 @@ public:
      * Skip native anonymous content created for placeholder of HTML input,
      * used in conjunction with eAllChildren or eAllButXBL.
      */
-    eSkipPlaceholderContent = 2
+    eSkipPlaceholderContent = 2,
+
+    /**
+     * Skip native anonymous content created by ancestor frames of the root
+     * element's primary frame, such as scrollbar elements created by the root
+     * scroll frame.
+     */
+    eSkipDocumentLevelNativeAnonymousContent = 4,
   };
 
   /**
@@ -723,10 +730,9 @@ public:
    */
   inline nsIContent *GetFlattenedTreeParent() const;
 
-  /**
-   * Helper method, which we leave public so that it's accessible from nsINode.
-   */
-  nsINode *GetFlattenedTreeParentNodeInternal() const;
+  // Helper method, which we leave public so that it's accessible from nsINode.
+  enum FlattenedParentType { eNotForStyle, eForStyle };
+  nsINode* GetFlattenedTreeParentNodeInternal(FlattenedParentType aType) const;
 
   /**
    * API to check if this is a link that's traversed in response to user input

dom/base/nsIContentInlines.h

@@ -33,14 +33,15 @@ inline mozilla::dom::ShadowRoot* nsIContent::GetShadowRoot() const
   return AsElement()->FastGetShadowRoot();
 }
 
-inline nsINode* nsINode::GetFlattenedTreeParentNode() const
+template<nsIContent::FlattenedParentType Type>
+static inline nsINode*
+GetFlattenedTreeParentNode(const nsINode* aNode)
 {
-  nsINode* parent = GetParentNode();
-
+  nsINode* parent = aNode->GetParentNode();
   // Try to short-circuit past the complicated and not-exactly-fast logic for
   // computing the flattened parent.
   //
-  // There are three cases where we need might something other than parentNode:
+  // There are four cases where we need might something other than parentNode:
   //   (1) The node is an explicit child of an XBL-bound element, re-bound
   //       to an XBL insertion point.
   //   (2) The node is a top-level element in a shadow tree, whose flattened
@@ -48,18 +49,31 @@ inline nsINode* nsINode::GetFlattenedTreeParentNode() const
   //       is the shadow root).
   //   (3) The node is an explicit child of an element with a shadow root,
   //       re-bound to an insertion point.
-  bool needSlowCall = HasFlag(NODE_MAY_BE_IN_BINDING_MNGR) ||
-                      IsInShadowTree() ||
-                      (parent && parent->IsContent() &&
-                       parent->AsContent()->GetShadowRoot());
+  //   (4) We want the flattened parent for style, and the node is the root
+  //       of a native anonymous content subtree parented to the document's
+  //       root element.
+  bool needSlowCall = aNode->HasFlag(NODE_MAY_BE_IN_BINDING_MNGR) ||
+                      aNode->IsInShadowTree() ||
+                      (parent &&
+                       parent->IsContent() &&
+                       parent->AsContent()->GetShadowRoot()) ||
+                      (Type == nsIContent::eForStyle &&
+                       aNode->IsContent() &&
+                       aNode->AsContent()->IsRootOfNativeAnonymousSubtree() &&
+                       aNode->OwnerDoc()->GetRootElement() == parent);
   if (MOZ_UNLIKELY(needSlowCall)) {
-    MOZ_ASSERT(IsContent());
-    return AsContent()->GetFlattenedTreeParentNodeInternal();
+    MOZ_ASSERT(aNode->IsContent());
+    return aNode->AsContent()->GetFlattenedTreeParentNodeInternal(Type);
   }
-
   return parent;
 }
 
+inline nsINode*
+nsINode::GetFlattenedTreeParentNode() const
+{
+  return ::GetFlattenedTreeParentNode<nsIContent::eNotForStyle>(this);
+}
+
 inline nsIContent*
 nsIContent::GetFlattenedTreeParent() const
 {
@@ -67,5 +81,10 @@ nsIContent::GetFlattenedTreeParent() const
   return (parent && parent->IsContent()) ? parent->AsContent() : nullptr;
 }
 
+inline nsINode*
+nsINode::GetFlattenedTreeParentNodeForStyle() const
+{
+  return ::GetFlattenedTreeParentNode<nsIContent::eForStyle>(this);
+}
 
 #endif // nsIContentInlines_h

dom/base/nsINode.h

@@ -920,6 +920,14 @@ public:
    */
   inline nsINode* GetFlattenedTreeParentNode() const;
 
+  /**
+   * Like GetFlattenedTreeParentNode, but returns null for any native
+   * anonymous content that was generated for ancestor frames of the
+   * root element's primary frame, such as scrollbar elements created
+   * by the root scroll frame.
+   */
+  inline nsINode* GetFlattenedTreeParentNodeForStyle() const;
+
   /**
    * Get the parent nsINode for this node if it is an Element.
    * @return the parent node

layout/generic/nsIAnonymousContentCreator.h

@@ -66,7 +66,9 @@ public:
    * Appends "native" anonymous children created by CreateAnonymousContent()
    * to the given content list depending on the filter.
    *
-   * @see nsIContent::GetChildren for set of values used for filter.
+   * @see nsIContent::GetChildren for set of values used for filter.  Currently,
+   *   eSkipPlaceholderContent is the only flag that any implementation of
+   *   this method heeds.
    */
   virtual void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                         uint32_t aFilter) = 0;

layout/style/DocumentStyleRootIterator.cpp

@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "DocumentStyleRootIterator.h"
+
+#include "nsContentUtils.h"
+
+namespace mozilla {
+
+DocumentStyleRootIterator::DocumentStyleRootIterator(nsIDocument* aDocument)
+  : mPosition(0)
+{
+  MOZ_COUNT_CTOR(DocumentStyleRootIterator);
+  if (Element* root = aDocument->GetRootElement()) {
+    mStyleRoots.AppendElement(root);
+  }
+  nsContentUtils::AppendDocumentLevelNativeAnonymousContentTo(
+      aDocument, mStyleRoots);
+}
+
+Element*
+DocumentStyleRootIterator::GetNextStyleRoot()
+{
+  for (;;) {
+    if (mPosition >= mStyleRoots.Length()) {
+      return nullptr;
+    }
+
+    nsIContent* next = mStyleRoots[mPosition];
+    ++mPosition;
+
+    if (next->IsElement()) {
+      return next->AsElement();
+    }
+  }
+}
+
+} // namespace mozilla

layout/style/DocumentStyleRootIterator.h

@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DocumentStyleRootIterator_h
+#define DocumentStyleRootIterator_h
+
+#include "nsTArray.h"
+
+class nsIContent;
+class nsIDocument;
+
+namespace mozilla {
+
+/**
+ * DocumentStyleRootIterator traverses the roots of the document from the
+ * perspective of the Servo-backed style system.  This will first traverse
+ * the document root, followed by any document level native anonymous content.
+ */
+class DocumentStyleRootIterator
+{
+public:
+  explicit DocumentStyleRootIterator(nsIDocument* aDocument);
+  ~DocumentStyleRootIterator() { MOZ_COUNT_DTOR(DocumentStyleRootIterator); }
+
+  Element* GetNextStyleRoot();
+
+private:
+  AutoTArray<nsIContent*, 8> mStyleRoots;
+  uint32_t mPosition;
+};
+
+} // namespace mozilla
+
+#endif // DocumentStyleRootIterator_h

layout/style/moz.build

@@ -88,6 +88,7 @@ EXPORTS.mozilla += [
     'CSSVariableValues.h',
     'DeclarationBlock.h',
     'DeclarationBlockInlines.h',
+    'DocumentStyleRootIterator.h',
     'HandleRefPtr.h',
     'IncrementalClearCOMRuleArray.h',
     'LayerAnimationInfo.h',
@@ -151,6 +152,7 @@ UNIFIED_SOURCES += [
     'CSSVariableResolver.cpp',
     'CSSVariableValues.cpp',
     'Declaration.cpp',
+    'DocumentStyleRootIterator.cpp',
     'ErrorReporter.cpp',
     'FontFace.cpp',
     'FontFaceSet.cpp',