Add public API for retrieving the extension object

Change-Id: I28bc1c177cb78d85d844c7a5cd5b6710db8fd65d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/qml/doc/src/qmlfunctions.qdoc

@@ -991,6 +991,16 @@
     \sa QML_ATTACHED(), {Providing Attached Properties}
 */
 
+/*!
+    \fn QObject *qmlExtendedObject(const QObject *base)
+    \relates QQmlEngine
+
+    This function returns the extension object that belongs to \a base, if there is any.
+    Otherwise it returns \c nullptr.
+
+    \sa QML_EXTENDED
+*/
+
 /*!
    \fn int qmlRegisterSingletonType(const char *uri, int versionMajor, int versionMinor, const char *typeName, QObject *(*callback)(QQmlEngine *, QJSEngine *))
    \relates QQmlEngine

src/qml/qml/qqml.cpp

@@ -149,6 +149,25 @@ QObject *qmlAttachedPropertiesObject(QObject *object, QQmlAttachedPropertiesFunc
     return resolveAttachedProperties(func, data, object, create);
 }
 
+QObject *qmlExtendedObject(QObject *object)
+{
+    if (!object)
+        return nullptr;
+
+    void *result = nullptr;
+    QObjectPrivate *d = QObjectPrivate::get(object);
+    if (!d->metaObject)
+        return nullptr;
+
+    const int id = d->metaObject->metaCall(
+                object, QMetaObject::CustomCall,
+                QQmlProxyMetaObject::ExtensionObjectId, &result);
+    if (id != QQmlProxyMetaObject::ExtensionObjectId)
+        return nullptr;
+
+    return static_cast<QObject *>(result);
+}
+
 int qmlRegisterUncreatableMetaObject(const QMetaObject &staticMetaObject,
                                      const char *uri, int versionMajor,
                                      int versionMinor, const char *qmlName,

src/qml/qml/qqml.h

@@ -615,6 +615,7 @@ Q_QML_EXPORT QQmlAttachedPropertiesFunc qmlAttachedPropertiesFunction(QObject *,
                                                                       const QMetaObject *);
 Q_QML_EXPORT QObject *qmlAttachedPropertiesObject(QObject *, QQmlAttachedPropertiesFunc func,
                                                   bool create = true);
+Q_QML_EXPORT QObject *qmlExtendedObject(QObject *);
 
 //The C++ version of protected namespaces in qmldir
 Q_QML_EXPORT bool qmlProtectModule(const char* uri, int majVersion);

src/qml/qml/qqmlproxymetaobject.cpp

@@ -104,39 +104,54 @@ int QQmlProxyMetaObject::metaCall(QObject *o, QMetaObject::Call c, int id, void
 {
     Q_ASSERT(object == o);
 
-    if ((c == QMetaObject::ReadProperty ||
-        c == QMetaObject::WriteProperty) &&
-            id >= metaObjects->constLast().propertyOffset) {
+    switch (c) {
+    case QMetaObject::ReadProperty:
+    case QMetaObject::WriteProperty: {
+        if (id < metaObjects->constLast().propertyOffset)
+            break;
 
         for (int ii = 0; ii < metaObjects->count(); ++ii) {
             const int globalPropertyOffset = metaObjects->at(ii).propertyOffset;
-            if (id >= globalPropertyOffset) {
-                QObject *proxy = getProxy(ii);
-                const int localProxyOffset = proxy->metaObject()->propertyOffset();
-                const int localProxyId = id - globalPropertyOffset + localProxyOffset;
+            if (id < globalPropertyOffset)
+                continue;
 
-                return proxy->qt_metacall(c, localProxyId, a);
-            }
+            QObject *proxy = getProxy(ii);
+            const int localProxyOffset = proxy->metaObject()->propertyOffset();
+            const int localProxyId = id - globalPropertyOffset + localProxyOffset;
+            return proxy->qt_metacall(c, localProxyId, a);
         }
-    } else if (c == QMetaObject::InvokeMetaMethod &&
-               id >= metaObjects->constLast().methodOffset) {
+        break;
+    }
+    case QMetaObject::InvokeMetaMethod: {
+        if (id < metaObjects->constLast().methodOffset)
+            break;
+
         QMetaMethod m = object->metaObject()->method(id);
         if (m.methodType() == QMetaMethod::Signal) {
             QMetaObject::activate(object, id, a);
             return -1;
-        } else {
-            for (int ii = 0; ii < metaObjects->count(); ++ii) {
-                const int globalMethodOffset = metaObjects->at(ii).methodOffset;
-                if (id >= globalMethodOffset) {
-                    QObject *proxy = getProxy(ii);
-
-                    const int localMethodOffset = proxy->metaObject()->methodOffset();
-                    const int localMethodId = id - globalMethodOffset + localMethodOffset;
-
-                    return proxy->qt_metacall(c, localMethodId, a);
-                }
-            }
         }
+
+        for (int ii = 0; ii < metaObjects->count(); ++ii) {
+            const int globalMethodOffset = metaObjects->at(ii).methodOffset;
+            if (id < globalMethodOffset)
+                continue;
+
+            QObject *proxy = getProxy(ii);
+            const int localMethodOffset = proxy->metaObject()->methodOffset();
+            const int localMethodId = id - globalMethodOffset + localMethodOffset;
+            return proxy->qt_metacall(c, localMethodId, a);
+        }
+
+        break;
+    }
+    case QMetaObject::CustomCall:
+        if (id != ExtensionObjectId)
+            break;
+        a[0] = getProxy(0);
+        return id;
+    default:
+        break;
     }
 
     if (parent)

src/qml/qml/qqmlproxymetaobject_p.h

@@ -65,6 +65,8 @@ QT_BEGIN_NAMESPACE
 class QQmlProxyMetaObject : public QDynamicMetaObjectData
 {
 public:
+    enum { ExtensionObjectId = std::numeric_limits<int>::min() };
+
     struct ProxyData {
         typedef QObject *(*CreateFunc)(QObject *);
         QMetaObject *metaObject;

tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp

@@ -5657,6 +5657,10 @@ void tst_qqmllanguage::extendedForeignTypes()
     QCOMPARE(o->property("foreignExtendedObjectName").toString(), QLatin1String("foreignExtended"));
     QCOMPARE(o->property("extendedInvokable").toInt(), 123);
     QCOMPARE(o->property("extendedSlot").toInt(), 456);
+
+    QObject *extension = qmlExtendedObject(extended);
+    QVERIFY(extension != nullptr);
+    QVERIFY(qobject_cast<Extension *>(extension) != nullptr);
 }
 
 void tst_qqmllanguage::foreignTypeSingletons() {