QmlCompiler: Correctly mark side effects for list operations

The contents of a QQmlListProperty are mutable even if the property is
not. This is because QQmlListProperty is only a view on a different
container.

Pick-to: 6.7
Fixes: QTBUG-123196
Change-Id: Id6309b1e1ddc219bf35e8d9888b8415dcc0f9d43
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 30 insertions, 0 deletions

diff --git a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
index 45f12ca506..3311c5a4c1 100644
--- a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
+++ b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
@@ -228,6 +228,7 @@ set(qml_files
     pressAndHoldButton.qml
     reduceWithNullThis.qml
     readEnumFromInstance.qml
+    readonlyListProperty.qml
     registerPropagation.qml
     registerelimination.qml
     renameAdjust.qml
diff --git a/tests/auto/qml/qmlcppcodegen/data/readonlyListProperty.qml b/tests/auto/qml/qmlcppcodegen/data/readonlyListProperty.qml
new file mode 100644
index 0000000000..149638283b
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/readonlyListProperty.qml
@@ -0,0 +1,17 @@
+import QtQml
+
+QtObject {
+    id: testObj
+
+    // "readonly" means the identity of the list cannot be changed.
+    // Its contents can be changed.
+    readonly default property list<QtObject> theList
+
+    Component.onCompleted: {
+        for (var i = 0; i < 4; i++)
+            testObj.theList.push(testObj)
+    }
+
+    property int l: theList.length
+}
+
diff --git a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
index 980ff1986b..fb1ab69c71 100644
--- a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
+++ b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
@@ -194,6 +194,7 @@ private slots:
     void propertyOfParent();
     void reduceWithNullThis();
     void readEnumFromInstance();
+    void readonlyListProperty();
     void registerElimination();
     void registerPropagation();
     void renameAdjust();
@@ -4025,6 +4026,17 @@ void tst_QmlCppCodegen::readEnumFromInstance()
     QCOMPARE(result, 0);
 }
 
+void tst_QmlCppCodegen::readonlyListProperty()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, QUrl(u"qrc:/qt/qml/TestTypes/readonlyListProperty.qml"_s));
+    QVERIFY2(component.isReady(), component.errorString().toUtf8());
+    QScopedPointer<QObject> object(component.create());
+    QVERIFY(!object.isNull());
+
+    QCOMPARE(object->property("l").toInt(), 4);
+}
+
 void tst_QmlCppCodegen::registerElimination()
 {
     QQmlEngine engine;