QmlDesigner: Block starting drag when clicking on non-draggable node

Fixes: QDS-6415
Change-Id: I328e7715d2837d1126506a6fbbf4d1bf52cc250f
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/qmldesigner/components/navigator/navigatortreeview.cpp

@@ -281,4 +281,20 @@ bool NavigatorTreeView::viewportEvent(QEvent *event)
     return QTreeView::viewportEvent(event);
 }
 
+void NavigatorTreeView::mousePressEvent(QMouseEvent *event)
+{
+    // Block drag from starting if press was on an item that is not draggable.
+    // This is necessary as it is the selected items that are dragged and the pressed item may not
+    // be a selected item, e.g. when pressing on locked item, leading to unexpected drags.
+    m_dragAllowed = model()->flags(indexAt(event->pos())) & Qt::ItemIsDragEnabled;
+
+    QTreeView::mousePressEvent(event);
+}
+
+void NavigatorTreeView::startDrag(Qt::DropActions supportedActions)
+{
+    if (m_dragAllowed)
+        QTreeView::startDrag(supportedActions);
+}
+
 }

src/plugins/qmldesigner/components/navigator/navigatortreeview.h

@@ -40,8 +40,13 @@ public:
     static void drawSelectionBackground(QPainter *painter, const QStyleOption &option);
     bool viewportEvent(QEvent *event) override;
 
+protected:
+    void mousePressEvent(QMouseEvent *event) override;
+    void startDrag(Qt::DropActions supportedActions) override;
+
 private:
     PreviewToolTip *m_previewToolTip = nullptr;
     qint32 m_previewToolTipNodeId = -1;
+    bool m_dragAllowed = true;
 };
 }