QQmlDelegateModel: De-bounce initialization of two-way bindings

When installing the reverse binding on a QQmlDelegateModelItem, the
binding is evaluated right away and tries to write the model data. We
don't want that since we know that the model data already contains the
same value.

Use a temporary filtering metaobject to block writes to this property
while installing the reverse binding. This causes the bounced write to
fail.

Amends commit 4bd5b31279

Pick-to: 6.10
Task-number: QTBUG-132420
Change-Id: Ib001f669046635cc3ae830154f22d95ee1d3924c
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

src/qmlmodels/qqmldelegatemodel.cpp

@@ -953,7 +953,8 @@ public:
         , access(access)
     {}
 
-    void operator()(const QMetaObject *modelMetaObject, QObject *modelObject) const
+    template<typename ModelObjectType>
+    void operator()(const QMetaObject *modelMetaObject, ModelObjectType *modelObject) const
     {
         const int end = modelMetaObject->propertyCount() + modelMetaObject->propertyOffset();
         for (int i = modelMetaObject->propertyOffset(); i < end; ++i) {
@@ -982,7 +983,18 @@ public:
             QQmlAnyBinding reverse = QQmlPropertyToPropertyBinding::create(
                     engine, targetProp, sourceProp);
             reverse.setSticky();
+            if constexpr (std::is_base_of_v<QQmlDelegateModelItem, ModelObjectType>) {
+                // Temporarily take away the metaobject so that the property can't actually be
+                // written. It shouldn't be written since we've just synchronized it the other way
+                // when installing the "forward" binding.
+                QQmlDelegateModelReadOnlyMetaObject readonly(modelObject, i);
                 reverse.installOn(sourceProp);
+            } else {
+                // It's only not a QQmlDelegateModelItem if the model is actually an ObjectModel.
+                // In that case, we hope that the generic equality check when setting a property
+                // is enough to de-bounce it.
+                reverse.installOn(sourceProp);
+            }
         }
     }
 

tests/auto/qml/qqmlrangemodel/tst_qqmlrangemodel.cpp

@@ -344,7 +344,6 @@ void tst_QQmlRangeModel::intRange()
     QCOMPARE(currentItem->property("currentValue"), oldValue);
 
     // nothing happened so far, so there shouldn't have been any calls to setData
-    QEXPECT_FAIL("ReadWrite", "Unexpected call to setData", Continue);
     QCOMPARE(model.setDataCalls, QList<int>{});
     model.setDataCalls.clear();
     model.dataCalls.clear();
@@ -383,14 +382,6 @@ void tst_QQmlRangeModel::objectRange()
     std::vector<Entry *> objects{entry.get()};
     RangeModel model(&objects);
 
-#ifndef QT_NO_DEBUG
-    // with ReadWrite, spurious call to setData(RangeModelDataRole) during loading
-    if (writeBack) {
-        QTest::ignoreMessage(QtCriticalMsg,
-                             QRegularExpression("Not able to assign QVariant\\(.*\\) to Entry*"));
-    }
-#endif
-
     auto view = makeView({
         {"delegateModelAccess", delegateModelAccess},
         {"model", QVariant::fromValue(&model)}
@@ -405,7 +396,6 @@ void tst_QQmlRangeModel::objectRange()
     QVERIFY(model.dataCalls.contains(Qt::RangeModelDataRole));
     model.dataCalls.clear();
     // there shouldn't have been any attempts to write yet
-    QEXPECT_FAIL("ReadWrite", "Premature calls to setData()", Continue);
     QCOMPARE(model.setDataCalls, QList<int>{});
     model.setDataCalls.clear();