qml: Override the new Object::instanceOf hook to allow QML type checking

[ChangeLog][QtQml] The instanceof keyword in JavaScript has been
extended to work on QML types and instances. This means that you are now
able to use it to verify that a var is indeed the type you expect (e.g.
someVar instanceof Rectangle).

Note that one of the added tests revealed a slight shortcoming in the
QML type system (QTBUG-58477). For now, we should keep consistency and
work to address the problem universally in the future.

Change-Id: I7d9bf9b64cfd037908de1ae51b01065eacb95abe
Task-number: QTBUG-24799
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/qml/qml/qqmltypewrapper.cpp b/src/qml/qml/qqmltypewrapper.cpp
index 49103ed653..7b98096a7f 100644
--- a/src/qml/qml/qqmltypewrapper.cpp
+++ b/src/qml/qml/qqmltypewrapper.cpp
@@ -342,4 +342,44 @@ bool QmlTypeWrapper::isEqualTo(Managed *a, Managed *b)
     return false;
 }
 
+ReturnedValue QmlTypeWrapper::instanceOf(const Object *typeObject, const Value &var)
+{
+    Q_ASSERT(typeObject->as<QV4::QmlTypeWrapper>());
+    const QV4::QmlTypeWrapper *typeWrapper = static_cast<const QV4::QmlTypeWrapper *>(typeObject);
+    QV4::ExecutionEngine *engine = typeObject->internalClass()->engine;
+    QQmlEnginePrivate *qenginepriv = QQmlEnginePrivate::get(engine->qmlEngine());
+
+    // can only compare a QObject* against a QML type
+    const QObjectWrapper *wrapper = var.as<QObjectWrapper>();
+    if (!wrapper)
+        return engine->throwTypeError();
+
+    // in case the wrapper outlived the QObject*
+    const QObject *wrapperObject = wrapper->object();
+    if (!wrapperObject)
+        return engine->throwTypeError();
+
+    const int myTypeId = typeWrapper->d()->type->typeId();
+    QQmlMetaObject myQmlType;
+    if (myTypeId == 0) {
+        // we're a composite type; a composite type cannot be equal to a
+        // non-composite object instance (Rectangle{} is never an instance of
+        // CustomRectangle)
+        QQmlData *theirDData = QQmlData::get(wrapperObject, /*create=*/false);
+        Q_ASSERT(theirDData); // must exist, otherwise how do we have a QObjectWrapper for it?!
+        if (!theirDData->compilationUnit)
+            return Encode(false);
+
+        QQmlTypeData *td = qenginepriv->typeLoader.getType(typeWrapper->d()->type->sourceUrl());
+        CompiledData::CompilationUnit *cu = td->compilationUnit();
+        myQmlType = qenginepriv->metaObjectForType(cu->metaTypeId);
+    } else {
+        myQmlType = qenginepriv->metaObjectForType(myTypeId);
+    }
+
+    const QMetaObject *theirType = wrapperObject->metaObject();
+
+    return QV4::Encode(QQmlMetaObject::canConvert(theirType, myQmlType));
+}
+
 QT_END_NAMESPACE