Fix ListModel.get(idx) == ListModel.get(idx)

This is a regression introduced with commit
4876ea6. Where we previously always
returned the same JS object, we would afterwards return a new JS object
for every invocation, which breaks reference comparison. As we store the
JS wrapper for the list element in the QQmlData->jsWrapper we can avoid
repeated allocations. In order for that wrapper to keep working after
modifications (insertion, etc.) to the list model, we have to replace
the static element index with a reference to the node model meta-object,
which also has an element index that however is kept up-to-date by the
list model itself.

Change-Id: I4368de6b6d86687fe96fbf73bd60b80b69d7b058
Task-number: QTBUG-52017
Reviewed-by: Michael Brasser <michael.brasser@live.com>
(cherry picked from commit 44a89492b49f23a975377795dbb7a48916cb5081)
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/qml/types/qqmllistmodel.cpp

@@ -1342,7 +1342,7 @@ void ModelObject::put(Managed *m, String *name, const Value &value)
     ModelObject *that = static_cast<ModelObject*>(m);
 
     ExecutionEngine *eng = that->engine();
-    const int elementIndex = that->d()->m_elementIndex;
+    const int elementIndex = that->d()->elementIndex();
     const QString propName = name->toQString();
     int roleIndex = that->d()->m_model->m_listModel->setExistingProperty(elementIndex, propName, value, eng);
     if (roleIndex != -1)
@@ -1369,7 +1369,7 @@ ReturnedValue ModelObject::get(const Managed *m, String *name, bool *hasProperty
                                                  QQmlPropertyCapture::OnlyOnce, false);
     }
 
-    const int elementIndex = that->d()->m_elementIndex;
+    const int elementIndex = that->d()->elementIndex();
     QVariant value = that->d()->m_model->data(elementIndex, role->index);
     return that->engine()->fromVariant(value);
 }
@@ -1387,7 +1387,7 @@ void ModelObject::advanceIterator(Managed *m, ObjectIterator *it, Value *name, u
         ScopedString roleName(scope, v4->newString(role.name));
         name->setM(roleName->d());
         *attributes = QV4::Attr_Data;
-        QVariant value = that->d()->m_model->data(that->d()->m_elementIndex, role.index);
+        QVariant value = that->d()->m_model->data(that->d()->elementIndex(), role.index);
         p->value = v4->fromVariant(value);
         return;
     }
@@ -2295,9 +2295,14 @@ QQmlV4Handle QQmlListModel::get(int index) const
             result = QV4::QObjectWrapper::wrap(scope.engine, object);
         } else {
             QObject *object = m_listModel->getOrCreateModelObject(const_cast<QQmlListModel *>(this), index);
-            result = scope.engine->memoryManager->allocObject<QV4::ModelObject>(object, const_cast<QQmlListModel *>(this), index);
-            // Keep track of the QObjectWrapper in persistent value storage
-            QQmlData::get(object)->jsWrapper.set(scope.engine, result);
+            QQmlData *ddata = QQmlData::get(object);
+            if (ddata->jsWrapper.isNullOrUndefined()) {
+                result = scope.engine->memoryManager->allocObject<QV4::ModelObject>(object, const_cast<QQmlListModel *>(this));
+                // Keep track of the QObjectWrapper in persistent value storage
+                ddata->jsWrapper.set(scope.engine, result);
+            } else {
+                result = ddata->jsWrapper.value();
+            }
         }
     }
 

src/qml/types/qqmllistmodel_p_p.h

@@ -164,15 +164,17 @@ namespace QV4 {
 namespace Heap {
 
 struct ModelObject : public QObjectWrapper {
-    void init(QObject *object, QQmlListModel *model, int elementIndex)
+    void init(QObject *object, QQmlListModel *model)
     {
         QObjectWrapper::init(object);
         m_model = model;
-        m_elementIndex = elementIndex;
+        QObjectPrivate *op = QObjectPrivate::get(object);
+        m_nodeModelMetaObject = static_cast<ModelNodeMetaObject *>(op->metaObject);
     }
     void destroy() { QObjectWrapper::destroy(); }
+    int elementIndex() const { return m_nodeModelMetaObject->m_elementIndex; }
     QQmlListModel *m_model;
-    int m_elementIndex;
+    ModelNodeMetaObject *m_nodeModelMetaObject;
 };
 
 }

tests/auto/qml/qqmllistmodel/tst_qqmllistmodel.cpp

@@ -449,6 +449,7 @@ void tst_qqmllistmodel::dynamic_data()
         QTest::newRow("get2") << "{get(-1) === undefined}" << 1 << "" << dr;
         QTest::newRow("get3") << "{append({'foo':123});get(0) != undefined}" << 1 << "" << dr;
         QTest::newRow("get4") << "{append({'foo':123});get(0).foo}" << 123 << "" << dr;
+        QTest::newRow("get5") << "{append({'foo':123});get(0) == get(0)}" << 1 << "" << dr;
         QTest::newRow("get-modify1") << "{append({'foo':123,'bar':456});get(0).foo = 333;get(0).foo}" << 333 << "" << dr;
         QTest::newRow("get-modify2") << "{append({'z':1});append({'foo':123,'bar':456});get(1).bar = 999;get(1).bar}" << 999 << "" << dr;