Bug 1848409 - Tweak the UpdateDefaultPreventedOnContent call to only special case the HTMLEditorEventListener case r=masayuki,dom-core

Calling `UpdateDefaultPreventedOnContent` separately from
`PreventDefault()` is error-prone. This patch should make it
safer.

Differential Revision: https://phabricator.services.mozilla.com/D186052

docshell/base/nsDocShellTreeOwner.cpp

@@ -924,10 +924,6 @@ nsDocShellTreeOwner::HandleEvent(Event* aEvent) {
     handler->CanDropLink(dragEvent, false, &canDropLink);
     if (canDropLink) {
       aEvent->PreventDefault();
-      WidgetDragEvent* asWidgetDropEvent =
-          dragEvent->WidgetEventPtr()->AsDragEvent();
-      asWidgetDropEvent->UpdateDefaultPreventedOnContent(
-          asWidgetDropEvent->mCurrentTarget);
     }
   } else if (eventType.EqualsLiteral("drop")) {
     nsCOMPtr<nsIWebNavigation> webnav =
@@ -979,10 +975,6 @@ nsDocShellTreeOwner::HandleEvent(Event* aEvent) {
     } else {
       aEvent->StopPropagation();
       aEvent->PreventDefault();
-      WidgetDragEvent* asWidgetDropEvent =
-          dragEvent->WidgetEventPtr()->AsDragEvent();
-      asWidgetDropEvent->UpdateDefaultPreventedOnContent(
-          asWidgetDropEvent->mCurrentTarget);
     }
   }
 

dom/events/Event.cpp

@@ -437,13 +437,39 @@ void Event::PreventDefaultInternal(bool aCalledByDefaultHandler,
     return;
   }
 
-  // If this is called by default handlers, the caller will call
+  if (mEvent->mClass == eDragEventClass) {
-  // UpdateDefaultPreventedOnContent when necessary.
+    UpdateDefaultPreventedOnContentForDragEvent();
-  if (!aCalledByDefaultHandler) {
+  }
-    if (WidgetDragEvent* dragEvent = mEvent->AsDragEvent()) {
+}
-      dragEvent->UpdateDefaultPreventedOnContent(dragEvent->mCurrentTarget);
+
+void Event::UpdateDefaultPreventedOnContentForDragEvent() {
+  WidgetDragEvent* dragEvent = mEvent->AsDragEvent();
+  if (!dragEvent) {
+    return;
+  }
+
+  nsIPrincipal* principal = nullptr;
+  // Since we now have HTMLEditorEventListener registered on nsWindowRoot,
+  // mCurrentTarget could be nsWindowRoot, so we need to use
+  // mTarget if that's the case.
+  MOZ_ASSERT_IF(dragEvent->mInHTMLEditorEventListener,
+                mEvent->mCurrentTarget->IsRootWindow());
+  EventTarget* target = dragEvent->mInHTMLEditorEventListener
+                            ? mEvent->mTarget
+                            : mEvent->mCurrentTarget;
+
+  nsINode* node = nsINode::FromEventTargetOrNull(target);
+  if (node) {
+    principal = node->NodePrincipal();
+  } else {
+    nsCOMPtr<nsIScriptObjectPrincipal> sop = do_QueryInterface(target);
+    if (sop) {
+      principal = sop->GetPrincipal();
     }
   }
+  if (principal && !principal->IsSystemPrincipal()) {
+    dragEvent->mDefaultPreventedOnContent = true;
+  }
 }
 
 void Event::SetEventType(const nsAString& aEventTypeArg) {

dom/events/Event.h

@@ -84,6 +84,8 @@ class Event : public nsISupports, public nsWrapperCache {
   void ConstructorInit(EventTarget* aOwner, nsPresContext* aPresContext,
                        WidgetEvent* aEvent);
 
+  void UpdateDefaultPreventedOnContentForDragEvent();
+
  public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(Event)

dom/events/MouseEvent.cpp

@@ -311,25 +311,6 @@ uint16_t MouseEvent::InputSource() const {
 }  // namespace mozilla::dom
 
 using namespace mozilla;
-
-void WidgetDragEvent::UpdateDefaultPreventedOnContent(
-    dom::EventTarget* aTarget) {
-  MOZ_ASSERT(DefaultPrevented());
-  nsIPrincipal* principal = nullptr;
-  nsINode* node = nsINode::FromEventTargetOrNull(aTarget);
-  if (node) {
-    principal = node->NodePrincipal();
-  } else {
-    nsCOMPtr<nsIScriptObjectPrincipal> sop = do_QueryInterface(aTarget);
-    if (sop) {
-      principal = sop->GetPrincipal();
-    }
-  }
-  if (principal && !principal->IsSystemPrincipal()) {
-    mDefaultPreventedOnContent = true;
-  }
-}
-
 using namespace mozilla::dom;
 
 already_AddRefed<MouseEvent> NS_NewDOMMouseEvent(EventTarget* aOwner,

editor/libeditor/EditorEventListener.cpp

@@ -875,10 +875,13 @@ nsresult EditorEventListener::DragOverOrDrop(DragEvent* aDragEvent) {
     return NS_OK;
   }
 
-  aDragEvent->PreventDefault();
-
   WidgetDragEvent* asWidgetEvent = aDragEvent->WidgetEventPtr()->AsDragEvent();
-  asWidgetEvent->UpdateDefaultPreventedOnContent(asWidgetEvent->mTarget);
+  AutoRestore<bool> inHTMLEditorEventListener(
+      asWidgetEvent->mInHTMLEditorEventListener);
+  if (mEditorBase->IsHTMLEditor()) {
+    asWidgetEvent->mInHTMLEditorEventListener = true;
+  }
+  aDragEvent->PreventDefault();
 
   aDragEvent->StopImmediatePropagation();
 

layout/forms/nsFileControlFrame.cpp

@@ -226,8 +226,6 @@ nsFileControlFrame::DnDListener::HandleEvent(Event* aEvent) {
   if (eventType.EqualsLiteral("dragover")) {
     // Prevent default if we can accept this drag data
     aEvent->PreventDefault();
-    WidgetDragEvent* asWidgetEvent = dragEvent->WidgetEventPtr()->AsDragEvent();
-    asWidgetEvent->UpdateDefaultPreventedOnContent(asWidgetEvent->mTarget);
     return NS_OK;
   }
 

widget/MouseEvents.h

@@ -347,7 +347,8 @@ class WidgetDragEvent : public WidgetMouseEvent {
       : WidgetMouseEvent(aIsTrusted, aMessage, aWidget, eDragEventClass, eReal,
                          aTime),
         mUserCancelled(false),
-        mDefaultPreventedOnContent(false) {}
+        mDefaultPreventedOnContent(false),
+        mInHTMLEditorEventListener(false) {}
 
   virtual WidgetEvent* Duplicate() const override {
     MOZ_ASSERT(mClass == eDragEventClass,
@@ -367,6 +368,8 @@ class WidgetDragEvent : public WidgetMouseEvent {
   bool mUserCancelled;
   // If this is true, the drag event's preventDefault() is called on content.
   bool mDefaultPreventedOnContent;
+  // If this event is currently being handled by HTMLEditorEventListener.
+  bool mInHTMLEditorEventListener;
 
   // XXX Not tested by test_assign_event_data.html
   void AssignDragEventData(const WidgetDragEvent& aEvent, bool aCopyTargets) {
@@ -378,8 +381,6 @@ class WidgetDragEvent : public WidgetMouseEvent {
     mDefaultPreventedOnContent = aEvent.mDefaultPreventedOnContent;
   }
 
-  void UpdateDefaultPreventedOnContent(dom::EventTarget* aTarget);
-
   /**
    * Should be called before dispatching the DOM tree if this event is
    * synthesized for tests because drop effect is initialized before