From d4f7cc1e851d03bcf653335c5228c342c41c25d9 Mon Sep 17 00:00:00 2001
From: Ehsan Akhgari <ehsan@mozilla.com>
Date: Sat, 26 Aug 2017 22:26:55 -0400
Subject: [PATCH] Bug 1392891 - Part 1: Make it possible to create
 nsContentList objects that don't observe DOM mutations; r=smaug

---
 dom/base/nsContentList.cpp | 25 +++++++++++++++++--------
 dom/base/nsContentList.h   | 18 ++++++++++++++----
 2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/dom/base/nsContentList.cpp b/dom/base/nsContentList.cpp
index 8a6da88bd982..86d72ab9d5bc 100644
--- a/dom/base/nsContentList.cpp
+++ b/dom/base/nsContentList.cpp
@@ -422,7 +422,8 @@ nsContentList::nsContentList(nsINode* aRootNode,
                              int32_t aMatchNameSpaceId,
                              nsIAtom* aHTMLMatchAtom,
                              nsIAtom* aXMLMatchAtom,
-                             bool aDeep)
+                             bool aDeep,
+                             bool aLiveList)
   : nsBaseContentList(),
     mRootNode(aRootNode),
     mMatchNameSpaceId(aMatchNameSpaceId),
@@ -434,7 +435,8 @@ nsContentList::nsContentList(nsINode* aRootNode,
     mState(LIST_DIRTY),
     mDeep(aDeep),
     mFuncMayDependOnAttr(false),
-    mIsHTMLDocument(aRootNode->OwnerDoc()->IsHTMLDocument())
+    mIsHTMLDocument(aRootNode->OwnerDoc()->IsHTMLDocument()),
+    mIsLiveList(aLiveList)
 {
   NS_ASSERTION(mRootNode, "Must have root");
   if (nsGkAtoms::_asterisk == mHTMLMatchAtom) {
@@ -444,7 +446,9 @@ nsContentList::nsContentList(nsINode* aRootNode,
   else {
     mMatchAll = false;
   }
-  mRootNode->AddMutationObserver(this);
+  if (mIsLiveList) {
+    mRootNode->AddMutationObserver(this);
+  }
 
   // We only need to flush if we're in an non-HTML document, since the
   // HTML5 parser doesn't need flushing.  Further, if we're not in a
@@ -462,7 +466,8 @@ nsContentList::nsContentList(nsINode* aRootNode,
                              bool aDeep,
                              nsIAtom* aMatchAtom,
                              int32_t aMatchNameSpaceId,
-                             bool aFuncMayDependOnAttr)
+                             bool aFuncMayDependOnAttr,
+                             bool aLiveList)
   : nsBaseContentList(),
     mRootNode(aRootNode),
     mMatchNameSpaceId(aMatchNameSpaceId),
@@ -475,10 +480,13 @@ nsContentList::nsContentList(nsINode* aRootNode,
     mMatchAll(false),
     mDeep(aDeep),
     mFuncMayDependOnAttr(aFuncMayDependOnAttr),
-    mIsHTMLDocument(false)
+    mIsHTMLDocument(false),
+    mIsLiveList(aLiveList)
 {
   NS_ASSERTION(mRootNode, "Must have root");
-  mRootNode->AddMutationObserver(this);
+  if (mIsLiveList) {
+    mRootNode->AddMutationObserver(this);
+  }
 
   // We only need to flush if we're in an non-HTML document, since the
   // HTML5 parser doesn't need flushing.  Further, if we're not in a
@@ -492,7 +500,7 @@ nsContentList::nsContentList(nsINode* aRootNode,
 nsContentList::~nsContentList()
 {
   RemoveFromHashtable();
-  if (mRootNode) {
+  if (mIsLiveList && mRootNode) {
     mRootNode->RemoveMutationObserver(this);
   }
 
@@ -646,7 +654,7 @@ void
 nsContentList::LastRelease()
 {
   RemoveFromCaches();
-  if (mRootNode) {
+  if (mIsLiveList && mRootNode) {
     mRootNode->RemoveMutationObserver(this);
     mRootNode = nullptr;
   }
@@ -1246,6 +1254,7 @@ nsLabelsNodeList::MaybeResetRoot(nsINode* aRootNode)
     return;
   }
 
+  MOZ_ASSERT(mIsLiveList, "nsLabelsNodeList is always a live list");
   if (mRootNode) {
     mRootNode->RemoveMutationObserver(this);
   }
diff --git a/dom/base/nsContentList.h b/dom/base/nsContentList.h
index a9f47cc82195..444bdf452620 100644
--- a/dom/base/nsContentList.h
+++ b/dom/base/nsContentList.h
@@ -251,8 +251,8 @@ struct nsContentListKey
 #define LIST_LAZY 2
 
 /**
- * Class that implements a live NodeList that matches Elements in the
- * tree based on some criterion.
+ * Class that implements a possibly live NodeList that matches Elements
+ * in the tree based on some criterion.
  */
 class nsContentList : public nsBaseContentList,
                       public nsIHTMLCollection,
@@ -276,12 +276,15 @@ public:
    * @param aDeep If false, then look only at children of the root, nothing
    *              deeper.  If true, then look at the whole subtree rooted at
    *              our root.
+   * @param aLiveList Whether the created list should be a live list observing
+   *                  mutations to the DOM tree.
    */
   nsContentList(nsINode* aRootNode,
                 int32_t aMatchNameSpaceId,
                 nsIAtom* aHTMLMatchAtom,
                 nsIAtom* aXMLMatchAtom,
-                bool aDeep = true);
+                bool aDeep = true,
+                bool aLiveList = true);
 
   /**
    * @param aRootNode The node under which to limit our search.
@@ -298,6 +301,8 @@ public:
    * @param aMatchNameSpaceId a namespace id to be passed back to aFunc
    * @param aFuncMayDependOnAttr a boolean that indicates whether this list is
    *                             sensitive to attribute changes.
+   * @param aLiveList Whether the created list should be a live list observing
+   *                  mutations to the DOM tree.
    */
   nsContentList(nsINode* aRootNode,
                 nsContentListMatchFunc aFunc,
@@ -306,7 +311,8 @@ public:
                 bool aDeep = true,
                 nsIAtom* aMatchAtom = nullptr,
                 int32_t aMatchNameSpaceId = kNameSpaceID_None,
-                bool aFuncMayDependOnAttr = true);
+                bool aFuncMayDependOnAttr = true,
+                bool aLiveList = true);
 
   // nsWrapperCache
   using nsWrapperCache::GetWrapperPreserveColor;
@@ -517,6 +523,10 @@ protected:
    * when doing function matching, always false otherwise.
    */
   uint8_t mIsHTMLDocument : 1;
+  /**
+   * Whether the list observes mutations to the DOM tree.
+   */
+  const uint8_t mIsLiveList : 1;
 
 #ifdef DEBUG_CONTENT_LIST
   void AssertInSync();