Bug 1794268 - Use WindowContext to check if drag source and drop target are in the same tab; r=webidl,smaug

Differential Revision: https://phabricator.services.mozilla.com/D163981

dom/base/ContentAreaDropListener.jsm

@@ -247,30 +247,19 @@ ContentAreaDropListener.prototype = {
       return true;
     }
 
-    let sourceNode = dataTransfer.mozSourceNode;
-    if (!sourceNode) {
+    // If this is an external drag, allow drop.
+    let sourceWC = dataTransfer.sourceWindowContext;
+    if (!sourceWC) {
       return true;
     }
 
-    // don't allow a drop of a node from the same document onto this one
-    let sourceDocument = sourceNode.ownerDocument;
-    let eventDocument = aEvent.originalTarget.ownerDocument;
-    if (sourceDocument == eventDocument) {
+    // If drag source and drop target are in the same top window, don't allow.
+    let eventWC =
+      aEvent.originalTarget.ownerGlobal.browsingContext.currentWindowContext;
+    if (eventWC && sourceWC.topWindowContext == eventWC.topWindowContext) {
       return false;
     }
 
-    // also check for nodes in other child or sibling frames by checking
-    // if both have the same top window.
-    if (sourceDocument && eventDocument) {
-      if (sourceDocument.defaultView == null) {
-        return true;
-      }
-      let sourceRoot = sourceDocument.defaultView.top;
-      if (sourceRoot && sourceRoot == eventDocument.defaultView.top) {
-        return false;
-      }
-    }
-
     return true;
   },
 

dom/events/DataTransfer.cpp

@@ -42,6 +42,7 @@
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/dom/OSFileSystem.h"
 #include "mozilla/dom/Promise.h"
+#include "mozilla/dom/WindowContext.h"
 #include "mozilla/Unused.h"
 #include "nsComponentManagerUtils.h"
 #include "nsNetUtil.h"
@@ -437,6 +438,17 @@ already_AddRefed<nsINode> DataTransfer::GetMozSourceNode() {
   return sourceNode.forget();
 }
 
+already_AddRefed<WindowContext> DataTransfer::GetSourceWindowContext() {
+  nsCOMPtr<nsIDragSession> dragSession = nsContentUtils::GetDragSession();
+  if (!dragSession) {
+    return nullptr;
+  }
+
+  RefPtr<WindowContext> sourceWindowContext;
+  dragSession->GetSourceWindowContext(getter_AddRefs(sourceWindowContext));
+  return sourceWindowContext.forget();
+}
+
 already_AddRefed<DOMStringList> DataTransfer::MozTypesAt(
     uint32_t aIndex, ErrorResult& aRv) const {
   // Only the first item is valid for clipboard events

dom/events/DataTransfer.h

@@ -42,6 +42,7 @@ class FileList;
 class Promise;
 template <typename T>
 class Optional;
+class WindowContext;
 
 #define NS_DATATRANSFER_IID                          \
   {                                                  \
@@ -253,6 +254,8 @@ class DataTransfer final : public nsISupports, public nsWrapperCache {
 
   already_AddRefed<nsINode> GetMozSourceNode();
 
+  already_AddRefed<WindowContext> GetSourceWindowContext();
+
   /*
    * Integer version of dropEffect, set to one of the constants in
    * nsIDragService.

dom/webidl/DataTransfer.webidl

@@ -151,6 +151,13 @@ partial interface DataTransfer {
   [UseCounter]
   readonly attribute Node? mozSourceNode;
 
+  /**
+   * The window context that mouse was pressed over to begin the drag. For
+   * external drags, this will be null.
+   */
+  [ChromeOnly]
+  readonly attribute WindowContext? sourceWindowContext;
+
   /**
    * The URI spec of the triggering principal.  This may be different than
    * sourceNode's principal when sourceNode is xul:browser and the drag is