QMainWindow: allow dropping QDockWidget to floating docks

In the QMainWindow::GroupedDragging mode, we can have floating
tabs of QDockWidget's, but it was not possible to drop onto
already floating QDockWidgets to tab them.

Task-number: QTBUG-47211
Change-Id: Ic666f6f8816d91a3eed844a6da1eb8698c8c7a0c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/widgets/widgets/qdockwidget.cpp b/src/widgets/widgets/qdockwidget.cpp
index 1b7473fbd7..6ea92e4c4d 100644
--- a/src/widgets/widgets/qdockwidget.cpp
+++ b/src/widgets/widgets/qdockwidget.cpp
@@ -760,7 +760,11 @@ void QDockWidgetPrivate::startDrag(bool group)
             QMainWindow::addDockWidget, so the QMainWindowLayout has no
             widget item for me. :( I have to create it myself, and then
             delete it if I don't get dropped into a dock area. */
-        state->widgetItem = new QDockWidgetItem(q);
+        QDockWidgetGroupWindow *floatingTab = qobject_cast<QDockWidgetGroupWindow*>(parent);
+        if (floatingTab && !q->isFloating())
+            state->widgetItem = new QDockWidgetGroupWindowItem(floatingTab);
+        else
+            state->widgetItem = new QDockWidgetItem(q);
         state->ownWidgetItem = true;
     }