QML: Allow namespaces as extensions to types

This way we can access the enums of namespaces as properties of the
primary type. This is achieved by:

1. Making enums of extended types available in the base type
2. Allowing the extension to be specified as plain metaObject rather
   than as type name.
3. Refraining from creating the extension if the create function does
   not exist.

The goal of this is to declare the Qt namespace in a civilized way, but
will also help with cleaning up the QtQuick value types and their enums.

Change-Id: I13399741d30ce38d1bff753cfa1b11e72ccfbf6a
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 15 insertions, 3 deletions

diff --git a/src/qml/qml/qqmlprivate.h b/src/qml/qml/qqmlprivate.h
index 6639ecbd26..2beeacd20f 100644
--- a/src/qml/qml/qqmlprivate.h
+++ b/src/qml/qml/qqmlprivate.h
@@ -625,6 +625,18 @@ namespace QQmlPrivate
     };
 
     template<class T, class = std::void_t<>>
+    struct QmlExtendedNamespace
+    {
+        static constexpr const QMetaObject *metaObject() { return nullptr; }
+    };
+
+    template<class T>
+    struct QmlExtendedNamespace<T, std::void_t<decltype(T::qmlExtendedNamespace())>>
+    {
+        static constexpr const QMetaObject *metaObject() { return T::qmlExtendedNamespace(); }
+    };
+
+    template<class T, class = std::void_t<>>
     struct QmlResolved
     {
         using Type = T;
@@ -718,7 +730,7 @@ namespace QQmlPrivate
     template<typename T, typename E>
     void qmlRegisterTypeAndRevisions(const char *uri, int versionMajor,
                                      const QMetaObject *classInfoMetaObject,
-                                     QVector<int> *qmlTypeIds)
+                                     QVector<int> *qmlTypeIds, const QMetaObject *extension)
     {
         RegisterTypeAndRevisions type = {
             0,
@@ -742,7 +754,7 @@ namespace QQmlPrivate
             StaticCastSelector<T, QQmlPropertyValueInterceptor>::cast(),
 
             ExtendedType<E>::createParent,
-            ExtendedType<E>::staticMetaObject(),
+            extension ? extension : ExtendedType<E>::staticMetaObject(),
 
             &qmlCreateCustomParser<T>,
             qmlTypeIds
@@ -754,7 +766,7 @@ namespace QQmlPrivate
     template<>
     void Q_QML_EXPORT qmlRegisterTypeAndRevisions<QQmlTypeNotAvailable, void>(
             const char *uri, int versionMajor, const QMetaObject *classInfoMetaObject,
-            QVector<int> *qmlTypeIds);
+            QVector<int> *qmlTypeIds, const QMetaObject *);
 
 } // namespace QQmlPrivate