Make QQmlValueTypeFactory::valueType() and isValueType() consistent

If isValueType() returns true, we should really return a non-null value
from valueType(). Otherwise the assumption that
QQmlValueTypeWrapper::valueType is never null breaks. In particular, the
unknown type and various primitive types are _not_ value types. We
special case the, probably common, UnknownType and check the actual
return value of valueType() for anything else. In order to avoid looking
up the metaobject each time we request a type that is not a value type,
we keep an invalid value type as marker for "not checked yet" and
replace that with nullptr once we determine that the type in question is
indeed not a value type.

Fixes: QTBUG-76866
Change-Id: I797f4cdd4db48ffc1b8fa2d919afc8022f67fa94
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/qml/qml/qqmlvaluetype_p.h b/src/qml/qml/qqmlvaluetype_p.h
index 89f1b71d61..cf53b8cb4a 100644
--- a/src/qml/qml/qqmlvaluetype_p.h
+++ b/src/qml/qml/qqmlvaluetype_p.h
@@ -66,6 +66,7 @@ QT_BEGIN_NAMESPACE
 class Q_QML_PRIVATE_EXPORT QQmlValueType : public QObject, public QAbstractDynamicMetaObject
 {
 public:
+    QQmlValueType();
     QQmlValueType(int userType, const QMetaObject *metaObject);
     ~QQmlValueType() override;
     void read(QObject *, int);
@@ -90,7 +91,7 @@ public:
 class Q_QML_PRIVATE_EXPORT QQmlValueTypeFactory
 {
 public:
-    static bool isValueType(int);
+    static bool isValueType(int idx);
     static QQmlValueType *valueType(int idx);
     static const QMetaObject *metaObjectForMetaType(int type);