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, 18 insertions, 1 deletions

diff --git a/src/widgets/widgets/qmainwindowlayout_p.h b/src/widgets/widgets/qmainwindowlayout_p.h
index 0c76a0ce90..9a13e5f5ce 100644
--- a/src/widgets/widgets/qmainwindowlayout_p.h
+++ b/src/widgets/widgets/qmainwindowlayout_p.h
@@ -92,6 +92,20 @@ protected:
     bool event(QEvent *) Q_DECL_OVERRIDE;
     void paintEvent(QPaintEvent*) Q_DECL_OVERRIDE;
 };
+
+// This item will be used in the layout for the gap item. We cannot use QWidgetItem directly
+// because QWidgetItem functions return an empty size for widgets that are are floating.
+class QDockWidgetGroupWindowItem : public QWidgetItem
+{
+public:
+    explicit QDockWidgetGroupWindowItem(QDockWidgetGroupWindow *parent) : QWidgetItem(parent) {}
+    QSize minimumSize() const Q_DECL_OVERRIDE { return lay()->minimumSize(); }
+    QSize maximumSize() const Q_DECL_OVERRIDE { return lay()->maximumSize(); }
+    QSize sizeHint() const Q_DECL_OVERRIDE { return lay()->sizeHint(); }
+
+private:
+    QLayout *lay() const { return const_cast<QDockWidgetGroupWindowItem *>(this)->widget()->layout(); }
+};
 #endif
 
 /* This data structure represents the state of all the tool-bars and dock-widgets. It's value based
@@ -288,7 +302,10 @@ public:
     QRect currentGapRect;
     QWidget *pluggingWidget;
 #ifndef QT_NO_RUBBERBAND
-    QRubberBand *gapIndicator;
+    QPointer<QRubberBand> gapIndicator;
+#endif
+#ifndef QT_NO_DOCKWIDGET
+    QPointer<QWidget> currentHoveredFloat; // set when dragging over a floating dock widget
 #endif
 
     void hover(QLayoutItem *widgetItem, const QPoint &mousePos);