Don't allow dropping into different mainWindows for now

kate/kateviewmanager.cpp

@@ -787,6 +787,13 @@ void KateViewManager::moveViewToViewSpace(KateViewSpace *dest, KateViewSpace *sr
 {
     // We always have an active view at this point which is what we are moving
     Q_ASSERT(activeView());
+
+    // Are we trying to drop into some other mainWindow of current app session?
+    // shouldn't happen, but just a safe guard
+    if (src->viewManger() != dest->viewManger()) {
+        return;
+    }
+
     auto view = src->takeView(doc);
     dest->addView(view);
     setActiveSpace(dest);

kate/kateviewspace.cpp

@@ -404,7 +404,6 @@ void KateViewSpace::registerDocument(KTextEditor::Document *doc)
     connect(m_tabBar, &KateTabBar::currentChanged, this, &KateViewSpace::changeView);
 }
 
-
 void KateViewSpace::closeDocument(KTextEditor::Document *doc)
 {
     // If this is the only view of the document,
@@ -431,10 +430,17 @@ void KateViewSpace::closeDocument(KTextEditor::Document *doc)
     }
 }
 
+bool KateViewSpace::acceptsDroppedTab(const class TabMimeData *tabMimeData)
+{
+    return tabMimeData && this != tabMimeData->sourceVS && // must not be same viewspace
+        viewManger() == tabMimeData->sourceVS->viewManger() && // for now we don't support dropping into different windows
+        !hasDocument(tabMimeData->doc);
+}
+
 void KateViewSpace::dragEnterEvent(QDragEnterEvent *e)
 {
     auto mimeData = qobject_cast<const TabMimeData *>(e->mimeData());
-    if (mimeData && this != mimeData->sourceVS && !hasDocument(mimeData->doc)) {
+    if (acceptsDroppedTab(mimeData)) {
         m_dropIndicator.reset(new QRubberBand(QRubberBand::Rectangle, this));
         m_dropIndicator->setGeometry(rect());
         m_dropIndicator->show();

kate/kateviewspace.h

@@ -44,6 +44,14 @@ public:
      */
     void setActive(bool active);
 
+    /**
+     * @return the view manager that this viewspace belongs to
+     */
+    KateViewManager *viewManger() const
+    {
+        return m_viewManager;
+    }
+
     /**
      * Create new view for given document
      * @param doc document to create view for
@@ -214,6 +222,7 @@ private Q_SLOTS:
     void createNewDocument();
 
 private:
+    bool acceptsDroppedTab(const class TabMimeData *tabMimeData);
     /**
      * Returns the amount of documents in KateDocManager that currently
      * have no tab in this tab bar.