QGraphicsProxyWidget: Don't crash within setWidget() when a child proxy has no assigned widget

QGraphicsProxyWidget::setWidget() is checking if the newly assigned
widget is already assigned to a child proxy widget without checking if
the child has a widget assigned at all which lead to a nullptr reference
if it is not the case.
Therefore check if the assigned widget is a valid pointer.

Fixes: QTBUG-15442
Change-Id: I006877f99895ca01975bdcad071cfcf90bea22ad
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp b/tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp
index 49afc5f369..4a301337ef 100644
--- a/tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp
+++ b/tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp
@@ -140,6 +140,7 @@ private slots:
     void palettePropagation();
     void fontPropagation();
     void dontCrashWhenDie();
+    void dontCrashNoParent();
     void createProxyForChildWidget();
 #ifndef QT_NO_CONTEXTMENU
     void actionsContextMenu();
@@ -2964,6 +2965,20 @@ void tst_QGraphicsProxyWidget::dontCrashWhenDie()
     qDeleteAll(QApplication::topLevelWidgets());
 }
 
+void tst_QGraphicsProxyWidget::dontCrashNoParent()  // QTBUG-15442
+{
+    QGraphicsProxyWidget *parent(new QGraphicsProxyWidget);
+    QGraphicsProxyWidget *child(new QGraphicsProxyWidget);
+    QScopedPointer<QLabel> label0(new QLabel);
+    QScopedPointer<QLabel> label1(new QLabel);
+
+    child->setParentItem(parent);
+    // Set the first label as the proxied widget.
+    parent->setWidget(label0.data());
+    // If we attempt to change the proxied widget we get a crash.
+    parent->setWidget(label1.data());
+}
+
 void tst_QGraphicsProxyWidget::createProxyForChildWidget()
 {
     QGraphicsScene scene;