Bug 1412775 - Implement Event.composedPath

Tag #1375

24 files changed, 194 insertions, 131 deletions

diff --git a/dom/archivereader/ArchiveRequest.cpp b/dom/archivereader/ArchiveRequest.cpp
index c4b19f56b..832dec3fa 100644
--- a/dom/archivereader/ArchiveRequest.cpp
+++ b/dom/archivereader/ArchiveRequest.cpp
@@ -72,7 +72,7 @@ nsresult
 ArchiveRequest::GetEventTargetParent(EventChainPreVisitor& aVisitor)
 {
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = nullptr;
+  aVisitor.SetParentTarget(nullptr, false);
   return NS_OK;
 }
 
diff --git a/dom/base/FragmentOrElement.cpp b/dom/base/FragmentOrElement.cpp
index ecb18798f..5b2fabd8d 100644
--- a/dom/base/FragmentOrElement.cpp
+++ b/dom/base/FragmentOrElement.cpp
@@ -813,6 +813,7 @@ nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   // Don't propagate mouseover and mouseout events when mouse is moving
   // inside chrome access only content.
   bool isAnonForEvents = IsRootOfChromeAccessOnlySubtree();
+  aVisitor.mRootOfClosedTree = isAnonForEvents;
   if ((aVisitor.mEvent->mMessage == eMouseOver ||
        aVisitor.mEvent->mMessage == eMouseOut ||
        aVisitor.mEvent->mMessage == ePointerOver ||
@@ -834,7 +835,7 @@ nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor)
         nsIContent* adjustedTarget =
           Event::GetShadowRelatedTarget(this, relatedTarget);
         if (this == adjustedTarget) {
-          aVisitor.mParentTarget = nullptr;
+          aVisitor.SetParentTarget(nullptr, false);
           aVisitor.mCanHandle = false;
           return NS_OK;
         }
@@ -891,7 +892,7 @@ nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor)
                         originalTarget->FindFirstNonChromeOnlyAccessContent())
                        ? "" : "Wrong event propagation!?!\n");
 #endif
-              aVisitor.mParentTarget = nullptr;
+              aVisitor.SetParentTarget(nullptr, false);
               // Event should not propagate to non-anon content.
               aVisitor.mCanHandle = isAnonForEvents;
               return NS_OK;
@@ -943,11 +944,17 @@ nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   if (!aVisitor.mEvent->mFlags.mComposedInNativeAnonymousContent &&
       IsRootOfNativeAnonymousSubtree() && OwnerDoc() &&
       OwnerDoc()->GetWindow()) {
-    aVisitor.mParentTarget = OwnerDoc()->GetWindow()->GetParentTarget();
+    aVisitor.SetParentTarget(OwnerDoc()->GetWindow()->GetParentTarget(), true);
   } else if (parent) {
-    aVisitor.mParentTarget = parent;
+    aVisitor.SetParentTarget(parent, false);
+    if (slot) {
+      ShadowRoot* root = slot->GetContainingShadow();
+      if (root && root->IsClosed()) {
+        aVisitor.mParentIsSlotInClosedTree = true;
+      }
+    }
   } else {
-    aVisitor.mParentTarget = GetComposedDoc();
+    aVisitor.SetParentTarget(GetComposedDoc(), false);
   }
   return NS_OK;
 }
diff --git a/dom/base/ShadowRoot.cpp b/dom/base/ShadowRoot.cpp
index 308f57cf7..e7f7ae93c 100644
--- a/dom/base/ShadowRoot.cpp
+++ b/dom/base/ShadowRoot.cpp
@@ -309,6 +309,7 @@ nsresult
 ShadowRoot::GetEventTargetParent(EventChainPreVisitor& aVisitor)
 {
   aVisitor.mCanHandle = true;
+  aVisitor.mRootOfClosedTree = IsClosed();
 
   // https://dom.spec.whatwg.org/#ref-for-get-the-parent%E2%91%A6
   if (!aVisitor.mEvent->mFlags.mComposed) {
@@ -323,13 +324,13 @@ ShadowRoot::GetEventTargetParent(EventChainPreVisitor& aVisitor)
       EventTarget* parentTarget = win && aVisitor.mEvent->mMessage != eLoad
         ? win->GetParentTarget() : nullptr;
 
-      aVisitor.mParentTarget = parentTarget;
+      aVisitor.SetParentTarget(parentTarget, true);
       return NS_OK;
     }
   }
 
   nsIContent* shadowHost = GetHost();
-  aVisitor.mParentTarget = shadowHost;
+  aVisitor.SetParentTarget(shadowHost, false);
 
   if (aVisitor.mOriginalTargetIsInAnon) {
     nsCOMPtr<nsIContent> content(do_QueryInterface(aVisitor.mEvent->mTarget));
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 459ad6bdd..d2763eddd 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -7531,8 +7531,8 @@ nsDocument::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   // Load events must not propagate to |window| object, see bug 335251.
   if (aVisitor.mEvent->mMessage != eLoad) {
     nsGlobalWindow* window = nsGlobalWindow::Cast(GetWindow());
-    aVisitor.mParentTarget =
-      window ? window->GetTargetForEventTargetChain() : nullptr;
+    aVisitor.SetParentTarget(
+      window ? window->GetTargetForEventTargetChain() : nullptr, false);
   }
   return NS_OK;
 }
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 802b44f38..69643762c 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -3608,7 +3608,7 @@ nsGlobalWindow::GetEventTargetParent(EventChainPreVisitor& aVisitor)
     }
   }
 
-  aVisitor.mParentTarget = GetParentTarget();
+  aVisitor.SetParentTarget(GetParentTarget(), true);
 
   // Handle 'active' event.
   if (!mIdleObservers.IsEmpty() &&
diff --git a/dom/base/nsInProcessTabChildGlobal.cpp b/dom/base/nsInProcessTabChildGlobal.cpp
index 547bb8d36..9885b41a8 100644
--- a/dom/base/nsInProcessTabChildGlobal.cpp
+++ b/dom/base/nsInProcessTabChildGlobal.cpp
@@ -270,7 +270,7 @@ nsInProcessTabChildGlobal::GetEventTargetParent(EventChainPreVisitor& aVisitor)
 #endif
 
   if (mPreventEventsEscaping) {
-    aVisitor.mParentTarget = nullptr;
+    aVisitor.SetParentTarget(nullptr, false);
     return NS_OK;
   }
 
@@ -278,11 +278,13 @@ nsInProcessTabChildGlobal::GetEventTargetParent(EventChainPreVisitor& aVisitor)
       (!mOwner || !nsContentUtils::IsInChromeDocshell(mOwner->OwnerDoc()))) {
     if (mOwner) {
       if (nsPIDOMWindowInner* innerWindow = mOwner->OwnerDoc()->GetInnerWindow()) {
-        aVisitor.mParentTarget = innerWindow->GetParentTarget();
+        // 'this' is already a "chrome handler", so we consider window's
+        // parent target to be part of that same part of the event path.
+        aVisitor.SetParentTarget(innerWindow->GetParentTarget(), false);
       }
     }
   } else {
-    aVisitor.mParentTarget = mOwner;
+    aVisitor.SetParentTarget(mOwner, false);
   }
 
   return NS_OK;
diff --git a/dom/base/nsWindowRoot.cpp b/dom/base/nsWindowRoot.cpp
index b629ab86f..710ecd88f 100644
--- a/dom/base/nsWindowRoot.cpp
+++ b/dom/base/nsWindowRoot.cpp
@@ -186,7 +186,7 @@ nsWindowRoot::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   aVisitor.mForceContentDispatch = true; //FIXME! Bug 329119
   // To keep mWindow alive
   aVisitor.mItemData = static_cast<nsISupports *>(mWindow);
-  aVisitor.mParentTarget = mParent;
+  aVisitor.SetParentTarget(mParent, false);
   return NS_OK;
 }
 
diff --git a/dom/events/DOMEventTargetHelper.cpp b/dom/events/DOMEventTargetHelper.cpp
index ee03463ef..90ee61059 100644
--- a/dom/events/DOMEventTargetHelper.cpp
+++ b/dom/events/DOMEventTargetHelper.cpp
@@ -331,7 +331,7 @@ nsresult
 DOMEventTargetHelper::GetEventTargetParent(EventChainPreVisitor& aVisitor)
 {
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = nullptr;
+  aVisitor.SetParentTarget(nullptr, false);
   return NS_OK;
 }
 
diff --git a/dom/events/Event.cpp b/dom/events/Event.cpp
index 280e40ad5..def298228 100755
--- a/dom/events/Event.cpp
+++ b/dom/events/Event.cpp
@@ -11,6 +11,7 @@
 #include "mozilla/dom/ShadowRoot.h"
 #include "mozilla/ContentEvents.h"
 #include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/EventDispatcher.h"
 #include "mozilla/EventStateManager.h"
 #include "mozilla/InternalMutationEvent.h"
 #include "mozilla/dom/Performance.h"
@@ -298,6 +299,12 @@ Event::GetCurrentTarget() const
   return mEvent->GetCurrentDOMEventTarget();
 }
 
+void
+Event::ComposedPath(nsTArray<RefPtr<EventTarget>>& aPath)
+{
+  EventDispatcher::GetComposedPathFor(mEvent, aPath);
+}
+
 NS_IMETHODIMP
 Event::GetCurrentTarget(nsIDOMEventTarget** aCurrentTarget)
 {
diff --git a/dom/events/Event.h b/dom/events/Event.h
index 0817aa809..4f1fcc827 100755
--- a/dom/events/Event.h
+++ b/dom/events/Event.h
@@ -157,6 +157,8 @@ public:
   EventTarget* GetTarget() const;
   EventTarget* GetCurrentTarget() const;
 
+  void ComposedPath(nsTArray<RefPtr<EventTarget>>& aPath);
+
   uint16_t EventPhase() const;
 
   // xpidl implementation
diff --git a/dom/events/EventDispatcher.cpp b/dom/events/EventDispatcher.cpp
index 740e611e4..1094c08c2 100644
--- a/dom/events/EventDispatcher.cpp
+++ b/dom/events/EventDispatcher.cpp
@@ -246,6 +246,36 @@ public:
     return mFlags.mPreHandleEventOnly;
   }
 
+  void SetRootOfClosedTree(bool aSet)
+  {
+    mFlags.mRootOfClosedTree = aSet;
+  }
+
+  bool IsRootOfClosedTree()
+  {
+    return mFlags.mRootOfClosedTree;
+  }
+
+  void SetIsSlotInClosedTree(bool aSet)
+  {
+    mFlags.mIsSlotInClosedTree = aSet;
+  }
+
+  bool IsSlotInClosedTree()
+  {
+    return mFlags.mIsSlotInClosedTree;
+  }
+
+  void SetIsChromeHandler(bool aSet)
+  {
+    mFlags.mIsChromeHandler = aSet;
+  }
+
+  bool IsChromeHandler()
+  {
+    return mFlags.mIsChromeHandler;
+  }
+
   void SetMayHaveListenerManager(bool aMayHave)
   {
     mFlags.mMayHaveManager = aMayHave;
@@ -344,6 +374,9 @@ private:
     bool mIsChromeContent : 1;
     bool mWantsPreHandleEvent : 1;
     bool mPreHandleEventOnly : 1;
+    bool mRootOfClosedTree : 1;
+    bool mIsSlotInClosedTree : 1;
+    bool mIsChromeHandler : 1;
   private:
     typedef uint32_t RawFlags;
     void SetRawFlags(RawFlags aRawFlags)
@@ -390,6 +423,7 @@ EventTargetChainItem::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   SetMayHaveListenerManager(aVisitor.mMayHaveListenerManager);
   SetWantsPreHandleEvent(aVisitor.mWantsPreHandleEvent);
   SetPreHandleEventOnly(aVisitor.mWantsPreHandleEvent && !aVisitor.mCanHandle);
+  SetRootOfClosedTree(aVisitor.mRootOfClosedTree);
   mItemFlags = aVisitor.mItemFlags;
   mItemData = aVisitor.mItemData;
 }
@@ -761,16 +795,19 @@ EventDispatcher::Dispatch(nsISupports* aTarget,
     targetEtci->SetNewTarget(t);
     EventTargetChainItem* topEtci = targetEtci;
     targetEtci = nullptr;
-    while (preVisitor.mParentTarget) {
-      EventTarget* parentTarget = preVisitor.mParentTarget;
+    while (preVisitor.GetParentTarget()) {
+      EventTarget* parentTarget = preVisitor.GetParentTarget();
       EventTargetChainItem* parentEtci =
-        EventTargetChainItem::Create(chain, preVisitor.mParentTarget, topEtci);
+        EventTargetChainItem::Create(chain, parentTarget, topEtci);
       if (!parentEtci->IsValid()) {
         EventTargetChainItem::DestroyLast(chain, parentEtci);
         rv = NS_ERROR_FAILURE;
         break;
       }
 
+      parentEtci->SetIsSlotInClosedTree(preVisitor.mParentIsSlotInClosedTree);
+      parentEtci->SetIsChromeHandler(preVisitor.mParentIsChromeHandler);
+
       // Item needs event retargetting.
       if (preVisitor.mEventTargetAtParent) {
         // Need to set the target of the event
@@ -814,9 +851,13 @@ EventDispatcher::Dispatch(nsISupports* aTarget,
         }
         // Handle the chain.
         EventChainPostVisitor postVisitor(preVisitor);
+        MOZ_RELEASE_ASSERT(!aEvent->mPath);
+        aEvent->mPath = &chain;
         EventTargetChainItem::HandleEventTargetChain(chain, postVisitor,
                                                      aCallback, cd);
 
+        aEvent->mPath = nullptr;
+
         preVisitor.mEventStatus = postVisitor.mEventStatus;
         // If the DOM event was created during event flow.
         if (!preVisitor.mDOMEvent && postVisitor.mDOMEvent) {
@@ -1128,4 +1169,64 @@ EventDispatcher::CreateEvent(EventTarget* aOwner,
   return nullptr;
 }
 
+// static
+void
+EventDispatcher::GetComposedPathFor(WidgetEvent* aEvent,
+                                    nsTArray<RefPtr<EventTarget>>& aPath)
+{
+  nsTArray<EventTargetChainItem>* path = aEvent->mPath;
+  if (!path || path->IsEmpty() || !aEvent->mCurrentTarget) {
+    return;
+  }
+
+  EventTarget* currentTarget =
+    aEvent->mCurrentTarget->GetTargetForEventTargetChain();
+  if (!currentTarget) {
+    return;
+  }
+
+  AutoTArray<EventTarget*, 128> reversedComposedPath;
+  bool hasSeenCurrentTarget = false;
+  uint32_t hiddenSubtreeLevel = 0;
+  for (uint32_t i = path->Length(); i; ) {
+    --i;
+
+    EventTargetChainItem& item = path->ElementAt(i);
+    if (item.PreHandleEventOnly()) {
+      continue;
+    }
+
+    if (!hasSeenCurrentTarget && currentTarget == item.CurrentTarget()) {
+      hasSeenCurrentTarget = true;
+    } else if (hasSeenCurrentTarget && item.IsRootOfClosedTree()) {
+      ++hiddenSubtreeLevel;
+    }
+
+    if (hiddenSubtreeLevel == 0) {
+      reversedComposedPath.AppendElement(item.CurrentTarget());
+    }
+
+    if (item.IsSlotInClosedTree() && hiddenSubtreeLevel > 0) {
+      --hiddenSubtreeLevel;
+    }
+
+    if (item.IsChromeHandler()) {
+      if (hasSeenCurrentTarget) {
+        // The current behavior is to include only EventTargets from
+        // either chrome side of event path or content side, not from both.
+        break;
+      }
+
+      // Need to start all over to collect the composed path on content side.
+      reversedComposedPath.Clear();
+    }
+  }
+
+  aPath.SetCapacity(reversedComposedPath.Length());
+  for (uint32_t i = reversedComposedPath.Length(); i; ) {
+    --i;
+    aPath.AppendElement(reversedComposedPath[i]->GetTargetForDOMEvent());
+  }
+}
+
 } // namespace mozilla
diff --git a/dom/events/EventDispatcher.h b/dom/events/EventDispatcher.h
index 618c863d5..8a34e6bf7 100644
--- a/dom/events/EventDispatcher.h
+++ b/dom/events/EventDispatcher.h
@@ -124,6 +124,9 @@ public:
     , mWantsWillHandleEvent(false)
     , mMayHaveListenerManager(true)
     , mWantsPreHandleEvent(false)
+    , mRootOfClosedTree(false)
+    , mParentIsSlotInClosedTree(false)
+    , mParentIsChromeHandler(false)
     , mParentTarget(nullptr)
     , mEventTargetAtParent(nullptr)
   {
@@ -139,10 +142,26 @@ public:
     mWantsWillHandleEvent = false;
     mMayHaveListenerManager = true;
     mWantsPreHandleEvent = false;
+    mRootOfClosedTree = false;
+    mParentIsSlotInClosedTree = false;
+    mParentIsChromeHandler = false;
     mParentTarget = nullptr;
     mEventTargetAtParent = nullptr;
   }
 
+  dom::EventTarget* GetParentTarget()
+  {
+    return mParentTarget;
+  }
+
+  void SetParentTarget(dom::EventTarget* aParentTarget, bool aIsChromeHandler)
+  {
+    mParentTarget = aParentTarget;
+    if (mParentTarget) {
+      mParentIsChromeHandler = aIsChromeHandler;
+    }
+  }
+
   /**
    * Member that must be set in GetEventTargetParent by event targets. If set to
    * false, indicates that this event target will not be handling the event and
@@ -195,10 +214,29 @@ public:
   bool mWantsPreHandleEvent;
 
   /**
+   * True if the current target is either closed ShadowRoot or root of
+   * chrome only access tree (for example native anonymous content).
+   */
+  bool mRootOfClosedTree;
+
+  /**
+   * True if mParentTarget is HTMLSlotElement in a closed shadow tree and the
+   * current target is assigned to that slot.
+   */
+  bool mParentIsSlotInClosedTree;
+
+  /**
+   * True if mParentTarget is a chrome handler in the event path.
+   */
+  bool mParentIsChromeHandler;
+
+private:
+  /**
    * Parent item in the event target chain.
    */
   dom::EventTarget* mParentTarget;
 
+public:
   /**
    * If the event needs to be retargeted, this is the event target,
    * which should be used when the event is handled at mParentTarget.
@@ -281,6 +319,9 @@ public:
                                                   WidgetEvent* aEvent,
                                                   const nsAString& aEventType);
 
+  static void GetComposedPathFor(WidgetEvent* aEvent,
+                                 nsTArray<RefPtr<dom::EventTarget>>& aPath);
+
   /**
    * Called at shutting down.
    */
diff --git a/dom/indexedDB/IDBFileHandle.cpp b/dom/indexedDB/IDBFileHandle.cpp
index 55dd22ce9..93e163c11 100644
--- a/dom/indexedDB/IDBFileHandle.cpp
+++ b/dom/indexedDB/IDBFileHandle.cpp
@@ -132,7 +132,7 @@ IDBFileHandle::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   AssertIsOnOwningThread();
 
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = mMutableFile;
+  aVisitor.SetParentTarget(mMutableFile, false);
   return NS_OK;
 }
 
diff --git a/dom/indexedDB/IDBFileRequest.cpp b/dom/indexedDB/IDBFileRequest.cpp
index 7d93f24de..1401f7c76 100644
--- a/dom/indexedDB/IDBFileRequest.cpp
+++ b/dom/indexedDB/IDBFileRequest.cpp
@@ -69,7 +69,7 @@ IDBFileRequest::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   AssertIsOnOwningThread();
 
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = mFileHandle;
+  aVisitor.SetParentTarget(mFileHandle, false);
   return NS_OK;
 }
 
diff --git a/dom/indexedDB/IDBRequest.cpp b/dom/indexedDB/IDBRequest.cpp
index b74725954..5ce077e33 100644
--- a/dom/indexedDB/IDBRequest.cpp
+++ b/dom/indexedDB/IDBRequest.cpp
@@ -454,7 +454,7 @@ IDBRequest::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   AssertIsOnOwningThread();
 
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = mTransaction;
+  aVisitor.SetParentTarget(mTransaction, false);
   return NS_OK;
 }
 
diff --git a/dom/indexedDB/IDBTransaction.cpp b/dom/indexedDB/IDBTransaction.cpp
index ec27c51d8..0a10e2ca0 100644
--- a/dom/indexedDB/IDBTransaction.cpp
+++ b/dom/indexedDB/IDBTransaction.cpp
@@ -1001,7 +1001,7 @@ IDBTransaction::GetEventTargetParent(EventChainPreVisitor& aVisitor)
   AssertIsOnOwningThread();
 
   aVisitor.mCanHandle = true;
-  aVisitor.mParentTarget = mDatabase;
+  aVisitor.SetParentTarget(mDatabase, false);
   return NS_OK;
 }
 
diff --git a/dom/webidl/Event.webidl b/dom/webidl/Event.webidl
index a5d7da7d4..8a8e71c43 100644
--- a/dom/webidl/Event.webidl
+++ b/dom/webidl/Event.webidl
@@ -22,6 +22,8 @@ interface Event {
   [Pure]
   readonly attribute EventTarget? currentTarget;
 
+  sequence<EventTarget> composedPath();
+
   const unsigned short NONE = 0;
   const unsigned short CAPTURING_PHASE = 1;
   const unsigned short AT_TARGET = 2;
diff --git a/dom/workers/SharedWorker.cpp b/dom/workers/SharedWorker.cpp
index 750dc9237..71c644405 100644
--- a/dom/workers/SharedWorker.cpp
+++ b/dom/workers/SharedWorker.cpp
@@ -196,7 +196,7 @@ SharedWorker::GetEventTargetParent(EventChainPreVisitor& aVisitor)
     QueueEvent(event);
 
     aVisitor.mCanHandle = false;
-    aVisitor.mParentTarget = nullptr;
+    aVisitor.SetParentTarget(nullptr, false);
     return NS_OK;
   }
 
diff --git a/dom/xul/nsXULElement.cpp b/dom/xul/nsXULElement.cpp
index af050d9f8..2ae03e0b1 100644
--- a/dom/xul/nsXULElement.cpp
+++ b/dom/xul/nsXULElement.cpp
@@ -1303,7 +1303,7 @@ nsXULElement::GetEventTargetParent(EventChainPreVisitor& aVisitor)
     if (IsEventStoppedFromAnonymousScrollbar(aVisitor.mEvent->mMessage)) {
         // Don't propagate these events from native anonymous scrollbar.
         aVisitor.mCanHandle = true;
-        aVisitor.mParentTarget = nullptr;
+        aVisitor.SetParentTarget(nullptr, false);
         return NS_OK;
     }
     if (aVisitor.mEvent->mMessage == eXULCommand &&
diff --git a/testing/web-platform/meta/shadow-dom/Extensions-to-Event-Interface.html.ini b/testing/web-platform/meta/shadow-dom/Extensions-to-Event-Interface.html.ini
index c58edca31..9760e42ea 100644
--- a/testing/web-platform/meta/shadow-dom/Extensions-to-Event-Interface.html.ini
+++ b/testing/web-platform/meta/shadow-dom/Extensions-to-Event-Interface.html.ini
@@ -1,13 +1,5 @@
 [Extensions-to-Event-Interface.html]
   type: testharness
-  [composedPath() must exist on Event]
-    expected: FAIL
-
-  [composedPath() must return an empty array when the event has not been dispatched]
-    expected: FAIL
-
-  [composedPath() must return an empty array when the event is no longer dispatched]
-    expected: FAIL
 
   [The event must propagate out of open mode shadow boundaries when the composed flag is set]
     expected: FAIL
diff --git a/testing/web-platform/meta/shadow-dom/event-composed-path-with-related-target.html.ini b/testing/web-platform/meta/shadow-dom/event-composed-path-with-related-target.html.ini
deleted file mode 100644
index afe0ce8b0..000000000
--- a/testing/web-platform/meta/shadow-dom/event-composed-path-with-related-target.html.ini
+++ /dev/null
@@ -1,48 +0,0 @@
-[event-composed-path-with-related-target.html]
-  type: testharness
-  expected: ERROR
-  [Event path for an event with a relatedTarget. relatedTarget != target.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event shoul be dispatched if 1) target and relatedTarget are same, and 2) they are not in a shadow tree.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event should stop at the shadow root]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event should not be dispatched if 1) target and relatedTarget are same, and 2) both are in a shadow tree.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. target and relaterTarget do not share any shadow-including ancestor. target is in a shadow tree.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. target and relaterTarget do not share any shadow-including ancestor. target is not in a shadow tree]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. target and relaterTarget share the same shadow-including ancestor. Both are in shadow trees.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. relaterTarget is a shadow-including ancestor of target.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. target is a shadow-including ancestor of relatedTarget.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. target is assigned to a slot.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. relatedTarget is assigned to a slot.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event should be dispatched at every slots.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event should be dispatched at every slots. relatedTarget should be correctly retargeted.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget. Event should be dispatched even when target and relatedTarget are same.]
-    expected: FAIL
-
-  [Event path for an event with a relatedTarget which is identical to target. Event should be dispatched and should stop at the shadow root.]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/shadow-dom/event-composed-path.html.ini b/testing/web-platform/meta/shadow-dom/event-composed-path.html.ini
index ecd6e3094..0566bf4f3 100644
--- a/testing/web-platform/meta/shadow-dom/event-composed-path.html.ini
+++ b/testing/web-platform/meta/shadow-dom/event-composed-path.html.ini
@@ -1,36 +1,9 @@
 [event-composed-path.html]
   type: testharness
-  expected: ERROR
-  [Event Path without ShadowRoots.]
-    expected: FAIL
-
-  [Event Path with an open ShadowRoot.]
-    expected: FAIL
-
-  [Event Path with a closed ShadowRoot.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: open > open.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: open > closed.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: closed > open.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: closed > closed.]
-    expected: FAIL
-
-  [Event Path with a slot in an open Shadow Root.]
-    expected: FAIL
 
   [Event Path with a slot in a closed Shadow Root.]
     expected: FAIL
 
-  [Event Path with slots in nested ShadowRoots: open > open.]
-    expected: FAIL
-
   [Event Path with slots in nested ShadowRoots: closed > closed.]
     expected: FAIL
 
diff --git a/testing/web-platform/meta/shadow-dom/event-composed.html.ini b/testing/web-platform/meta/shadow-dom/event-composed.html.ini
deleted file mode 100644
index 6386a51c5..000000000
--- a/testing/web-platform/meta/shadow-dom/event-composed.html.ini
+++ /dev/null
@@ -1,23 +0,0 @@
-[event-composed.html]
-  type: testharness
-  [An event should be scoped by default]
-    expected: FAIL
-
-  [An event should not be scoped if composed is specified]
-    expected: FAIL
-
-  [A synthetic MouseEvent should be scoped by default]
-    expected: FAIL
-
-  [A synthetic MouseEvent with composed=true should not be scoped]
-    expected: FAIL
-
-  [A synthetic FocusEvent should be scoped by default]
-    expected: FAIL
-
-  [A synthetic FocusEvent with composed=true should not be scoped]
-    expected: FAIL
-
-  [A UA click event should not be scoped]
-    expected: FAIL
-
diff --git a/widget/BasicEvents.h b/widget/BasicEvents.h
index 960cb67c6..4e9e0e6ce 100644
--- a/widget/BasicEvents.h
+++ b/widget/BasicEvents.h
@@ -25,6 +25,8 @@ struct ParamTraits;
 
 namespace mozilla {
 
+class EventTargetChainItem;
+
 /******************************************************************************
  * mozilla::BaseEventFlags
  *
@@ -350,6 +352,7 @@ protected:
     , mRefPoint(0, 0)
     , mLastRefPoint(0, 0)
     , mSpecifiedEventType(nullptr)
+    , mPath(nullptr)
   {
     MOZ_COUNT_CTOR(WidgetEvent);
     mFlags.Clear();
@@ -361,6 +364,7 @@ protected:
 
   WidgetEvent()
     : WidgetEventTime()
+    , mPath(nullptr)
   {
     MOZ_COUNT_CTOR(WidgetEvent);
   }
@@ -419,6 +423,8 @@ public:
   nsCOMPtr<dom::EventTarget> mCurrentTarget;
   nsCOMPtr<dom::EventTarget> mOriginalTarget;
 
+  nsTArray<EventTargetChainItem>* mPath;
+
   dom::EventTarget* GetDOMEventTarget() const;
   dom::EventTarget* GetCurrentDOMEventTarget() const;
   dom::EventTarget* GetOriginalDOMEventTarget() const;