Ensure identical behavior for singleton types defined in C++ and QML

Singleton types defined in C++ have no QML context. Therefore, both
qmlContext(obj) and qmlEngine(obj) return zero. Although documented,
this behavior is surprising and inconsistent with singleton types defined
in QML. The current behavior was decided upon in QTBUG-23116.

This patch puts C++ singleton types into a sub-context of the root context
by default, just like it is the case for QML-defined singleton types. This
doesn't cause any harm, but avoids surprises. It also fixes a bug in
QmlTypeWrapper that returned an invalid QVariant for QJSValue singletons.

Task-number: QTBUG-38583
Change-Id: Id1d48ecdc49f0e22714857a1b49b457885889e5e
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

3 files changed, 42 insertions, 2 deletions

diff --git a/tests/auto/qml/qqmllanguage/data/singletonTest18.qml b/tests/auto/qml/qqmllanguage/data/singletonTest18.qml
new file mode 100644
index 0000000000..7616c23531
--- /dev/null
+++ b/tests/auto/qml/qqmllanguage/data/singletonTest18.qml
@@ -0,0 +1,9 @@
+import QtQuick 2.0
+import "singleton"
+import Test 1.0
+
+Item {
+    property var qmlSingleton: SingletonType
+    property var jsSingleton: MyQJSValueQObjectSingleton
+    property var cppSingleton: MyTypeObjectSingleton
+}
diff --git a/tests/auto/qml/qqmllanguage/testtypes.cpp b/tests/auto/qml/qqmllanguage/testtypes.cpp
index 0eb4f26878..7e247b1906 100644
--- a/tests/auto/qml/qqmllanguage/testtypes.cpp
+++ b/tests/auto/qml/qqmllanguage/testtypes.cpp
@@ -35,6 +35,14 @@ static QObject *myTypeObjectSingleton(QQmlEngine *engine, QJSEngine *scriptEngin
     return new MyTypeObject();
 }
 
+static QJSValue myQJSValueQObjectSingleton(QQmlEngine *engine, QJSEngine *scriptEngine)
+{
+    Q_UNUSED(engine)
+
+    QJSValue value = scriptEngine->newQObject(new MyTypeObject());
+    return value;
+}
+
 void registerTypes()
 {
     qmlRegisterInterface<MyInterface>("MyInterface");
@@ -101,6 +109,7 @@ void registerTypes()
     qmlRegisterType<MyCompositeBaseType>("Test", 1, 0, "MyCompositeBaseType");
 
     qmlRegisterSingletonType<MyTypeObjectSingleton>("Test", 1, 0, "MyTypeObjectSingleton", myTypeObjectSingleton);
+    qmlRegisterSingletonType("Test", 1, 0, "MyQJSValueQObjectSingleton", myQJSValueQObjectSingleton);
 
     qmlRegisterType<MyArrayBufferTestClass>("Test", 1, 0, "MyArrayBufferTestClass");
 
diff --git a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
index 400c28928a..39f973f3fd 100644
--- a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
+++ b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
@@ -246,6 +246,8 @@ private slots:
     void compositeSingletonRegistered();
     void compositeSingletonCircular();
 
+    void singletonsHaveContextAndEngine();
+
     void customParserBindingScopes();
     void customParserEvaluateEnum();
     void customParserProperties();
@@ -3923,11 +3925,13 @@ void tst_qqmllanguage::getSingletonInstance(QObject* o, const char* propertyName
         return;
 
     QVariant variant = o->property(propertyName);
-    QVERIFY(variant.userType() == qMetaTypeId<QObject *>());
+    QVERIFY(variant.isValid());
 
     QObject *singleton = nullptr;
-    if (variant.canConvert<QObject*>())
+    if (variant.userType() == qMetaTypeId<QObject *>())
         singleton = variant.value<QObject*>();
+    else if (variant.userType() == qMetaTypeId<QJSValue>())
+        singleton = variant.value<QJSValue>().toQObject();
 
     QVERIFY(singleton != nullptr);
     *result = singleton;
@@ -4232,6 +4236,24 @@ void tst_qqmllanguage::compositeSingletonCircular()
     QCOMPARE(o->property("value").toInt(), 2);
 }
 
+void tst_qqmllanguage::singletonsHaveContextAndEngine()
+{
+    QObject *qmlSingleton = nullptr;
+    getSingletonInstance(engine, "singletonTest18.qml", "qmlSingleton", &qmlSingleton);
+    QVERIFY(qmlContext(qmlSingleton));
+    QCOMPARE(qmlEngine(qmlSingleton), &engine);
+
+    QObject *jsSingleton = nullptr;
+    getSingletonInstance(engine, "singletonTest18.qml", "jsSingleton", &jsSingleton);
+    QVERIFY(qmlContext(jsSingleton));
+    QCOMPARE(qmlEngine(jsSingleton), &engine);
+
+    QObject *cppSingleton = nullptr;
+    getSingletonInstance(engine, "singletonTest18.qml", "cppSingleton", &cppSingleton);
+    QVERIFY(qmlContext(cppSingleton));
+    QCOMPARE(qmlEngine(cppSingleton), &engine);
+}
+
 void tst_qqmllanguage::customParserBindingScopes()
 {
     QQmlComponent component(&engine, testFile("customParserBindingScopes.qml"));