Templates: Disconnect menu bar items when clearing

Otherwise we get change notifications for half-dead change listeners and
subsequent crashes.

Pick-to: 6.10 6.9 6.8 6.5
Task-number: QTBUG-137554
Change-Id: I194ca0f8c3a540b1bfc41fa969d0cd3b9e6c24e4
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/quicktemplates/qquickmenubar.cpp

@@ -339,7 +339,8 @@ QQuickMenu *QQuickMenuBarPrivate::menus_at(QQmlListProperty<QQuickMenu> *prop, q
 void QQuickMenuBarPrivate::menus_clear(QQmlListProperty<QQuickMenu> *prop)
 {
     QQuickMenuBar *menuBar = static_cast<QQuickMenuBar *>(prop->object);
-    QQuickMenuBarPrivate::get(menuBar)->contentModel->clear();
+    for (int count = menuBar->count(); count > 0; count = menuBar->count())
+        menuBar->takeMenu(count - 1);
 }
 
 QPalette QQuickMenuBarPrivate::defaultPalette() const

tests/auto/quickcontrols/qquickmenubar/data/clearMenus.qml

@@ -0,0 +1,35 @@
+import QtQuick
+import QtQuick.Templates
+
+Item {
+    property int v: 0
+
+    MenuBar {
+        id: menuBar
+        Menu {}
+    }
+
+    Instantiator {
+        id: instantiator
+
+        delegate: Menu {}
+
+        onObjectAdded: (index, object) => {
+            menuBar.menus.push(object)
+        }
+
+        onObjectRemoved: (index, object) => {
+            menuBar.menus.length = 0;
+        }
+    }
+
+    Timer {
+        running: v < 2
+        interval: 1
+        repeat: true
+
+        onTriggered: {
+            instantiator.model = (++v % 2) ? 0 : 2
+        }
+    }
+}

tests/auto/quickcontrols/qquickmenubar/tst_qquickmenubar.cpp

@@ -82,6 +82,7 @@ private slots:
     void panMenuBar_data();
     void panMenuBar();
     void dontDeleteDelegates();
+    void clearMenus();
 
 private:
     bool nativeMenuBarSupported = false;
@@ -1896,6 +1897,16 @@ void tst_qquickmenubar::dontDeleteDelegates()
     QVERIFY(delegateComponent2);
 }
 
+void tst_qquickmenubar::clearMenus()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("clearMenus.qml"));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+    QTRY_COMPARE(o->property("v").toInt(), 2);
+}
+
 QTEST_QUICKCONTROLS_MAIN(tst_qquickmenubar)
 
 #include "tst_qquickmenubar.moc"