QML: Fix conflicts between QML_ANONYMOUS, QML_UNCREATABLE and namespaces

Even though it makes no sense, we have to allow QML_ANONYMOUS and
QML_UNCREATABLE in the same class since we've documented it. You
cannot trigger the custom message because you'd need a name to attempt
to create an instance of the type. Therefore, the documentation
suggesting this is nonsensical.

In theory you could indeed provide a custom message for namespaces, but
in order to continue supporting this, we would either have to drop the
QmlIsUncreatable mechanism, or we would need a different macro. So,
let's drop this for now. If we really need it, we can introduce a
different macro later.

[ChangeLog][QtQml][Important Behavior Changes] You can no longer
override the "uncreatable" message for QML-exposed namespaces using
QML_UNCREATABLE. This would be incompatible with making the
QML_UNCREATABLE macro safe from unintended inheritance. The latter is
much more important.

Fixes: QTBUG-111470
Change-Id: Ib736a2411128d58d939fa2a57d28a0b31c0777e6
Reviewed-by: Robert Griebl <robert.griebl@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit a60968283b)

src/qml/doc/src/qmlfunctions.qdoc

@@ -153,8 +153,7 @@
 
   Some QML types are implicitly uncreatable, in particular types exposed with
   \l QML_ANONYMOUS or namespaces exposed with \l QML_ELEMENT or
-  \l QML_NAMED_ELEMENT(). For such types, \l QML_UNCREATABLE() can be used to
-  provide a custom error message.
+  \l QML_NAMED_ELEMENT().
 
   Since Qt 6.0 you can use "" instead of a reason to use a standard message instead.
 

src/qml/qml/qqml.h

@@ -891,7 +891,7 @@ void qmlRegisterTypesAndRevisions(const char *uri, int versionMajor, QList<int>
             QQmlPrivate::QmlSingleton<T>::Value,
             QQmlPrivate::QmlInterface<T>::Value,
             QQmlPrivate::QmlSequence<T>::Value,
-            QQmlPrivate::QmlUncreatable<T>::Value>
+            QQmlPrivate::QmlUncreatable<T>::Value || QQmlPrivate::QmlAnonymous<T>::Value>
             ::registerTypeAndRevisions(uri, versionMajor, qmlTypeIds,
                                        QQmlPrivate::QmlExtendedNamespace<T>::metaObject()), ...);
 }

src/qml/qml/qqmlprivate.h

@@ -897,6 +897,20 @@ namespace QQmlPrivate
                 && bool(T::QmlIsUncreatable::yes);
     };
 
+    template<class T, class = std::void_t<>>
+    struct QmlAnonymous
+    {
+        static constexpr bool Value = false;
+    };
+
+    template<class T>
+    struct QmlAnonymous<T, std::void_t<typename T::QmlIsAnonymous>>
+    {
+        static constexpr bool Value =
+                QmlTypeHasMarker<T, decltype(&T::qt_qmlMarker_anonymous)>::value
+                && bool(T::QmlIsAnonymous::yes);
+    };
+
 
     template<class T, class = std::void_t<>>
     struct QmlSingleton

src/qmlintegration/qqmlintegration.h

@@ -18,6 +18,8 @@ namespace QQmlPrivate {
     struct QmlExtendedNamespace;
     template<class, class>
     struct QmlUncreatable;
+    template<class, class>
+    struct QmlAnonymous;
 }
 
 template <typename T> class QList;
@@ -41,11 +43,11 @@ QT_END_NAMESPACE
 
 #define QML_ANONYMOUS \
     Q_CLASSINFO("QML.Element", "anonymous") \
-    enum class QmlIsUncreatable {yes = true}; \
-    template<typename, typename> friend struct QML_PRIVATE_NAMESPACE::QmlUncreatable; \
+    enum class QmlIsAnonymous{yes = true}; \
+    template<typename, typename> friend struct QML_PRIVATE_NAMESPACE::QmlAnonymous; \
     template<typename... Args> \
     friend void QML_REGISTER_TYPES_AND_REVISIONS(const char *uri, int versionMajor, QList<int> *); \
-    inline constexpr void qt_qmlMarker_uncreatable() {}
+    inline constexpr void qt_qmlMarker_anonymous() {}
 
 #define QML_NAMED_ELEMENT(NAME) \
     Q_CLASSINFO("QML.Element", #NAME)

tests/auto/qml/qmltyperegistrar/tst_qmltyperegistrar.cpp

@@ -573,4 +573,15 @@ void tst_qmltyperegistrar::baseVersionInQmltypes()
     QVERIFY(qmltypesData.contains("exports: [\"QmlTypeRegistrarTest/WithMethod 1.0\"]"));
 }
 
+void tst_qmltyperegistrar::anonymousAndUncreatable()
+{
+    QVERIFY(qmltypesData.contains(
+    R"(Component {
+        file: "tst_qmltyperegistrar.h"
+        name: "AnonymousAndUncreatable"
+        accessSemantics: "reference"
+        prototype: "QObject"
+    })"));
+}
+
 QTEST_MAIN(tst_qmltyperegistrar)

tests/auto/qml/qmltyperegistrar/tst_qmltyperegistrar.h

@@ -501,6 +501,13 @@ signals:
     void clonedSignal(int i = 7);
 };
 
+class AnonymousAndUncreatable : public QObject
+{
+     Q_OBJECT
+     QML_ANONYMOUS
+     QML_UNCREATABLE("Pointless uncreatable message")
+};
+
 class tst_qmltyperegistrar : public QObject
 {
     Q_OBJECT
@@ -549,6 +556,7 @@ private slots:
     void duplicateExportWarnings();
     void clonedSignal();
     void baseVersionInQmltypes();
+    void anonymousAndUncreatable();
 
 private:
     QByteArray qmltypesData;