It's possible to register already defined enum for MOC?

Question

For instance I have enum from thirdparty library:

namespace Lib {
  enum class Foo {
    Bar,
    Baz
  };
};

I have tried use next wrapper

namespace Qml {
    Q_NAMESPACE
    using Foo = Lib::Foo;
    Q_ENUMS(Foo)
}

with qmlRegisterUncreatableMetaObject, but its don't work for me.

Can I register one in Meta Object System for using in QML, but without duplicates like:

class QmlObject {
    Q_GADGET

public:
    enum Foo {
        Bar = Lib::Bar,
        Baz = Lib::Baz
    };
    Q_ENUM(Foo)
};

Version of Qt is 5.15.2. Thanks.

Answer 1

I have found solution using the library magic_enum (at least v0.8.1, see limitations) and bit of modification in implementation of qmlRegisterType:

#include <QtQml/qqmlprivate.h>
#include <QtCore/private/qmetaobjectbuilder_p.h>
#include <magic_enum.hpp>
    
template<class T, class ... En>
int qmlRegisterTypeWithEnums(const char *uri, int versionMajor, int versionMinor, const char *qmlName)
{
    QML_GETTYPENAMES

    //! register our enums here
    QMetaObjectBuilder builder(&T::staticMetaObject);

    ([](QMetaObjectBuilder & builder)
    {
        QMetaEnumBuilder enumBuilder {
            builder.addEnumerator(QByteArray::fromStdString(std::string{magic_enum::enum_type_name<En>()}))
        };
        enumBuilder.setIsScoped(magic_enum::is_scoped_enum_v<En>);
        constexpr auto entries = magic_enum::enum_entries<En>();
        for (const auto & pair : entries) {
            enumBuilder.addKey(QByteArray::fromStdString(std::string{pair.second}), static_cast<int>(pair.first));
        }
    }(builder), ...);
    //! ***************************

    QQmlPrivate::RegisterType type = {
        0,

        qRegisterNormalizedMetaType<T *>(pointerName.constData()),
        qRegisterNormalizedMetaType<QQmlListProperty<T> >(listName.constData()),
        sizeof(T), QQmlPrivate::createInto<T>,
        QString(),

        uri, versionMajor, versionMinor, qmlName, builder.toMetaObject(),

        QQmlPrivate::attachedPropertiesFunc<T>(),
        QQmlPrivate::attachedPropertiesMetaObject<T>(),

        QQmlPrivate::StaticCastSelector<T,QQmlParserStatus>::cast(),
        QQmlPrivate::StaticCastSelector<T,QQmlPropertyValueSource>::cast(),
        QQmlPrivate::StaticCastSelector<T,QQmlPropertyValueInterceptor>::cast(),

        nullptr, nullptr,

        nullptr,
        0
    };

    return QQmlPrivate::qmlregister(QQmlPrivate::TypeRegistration, &type);
}

Now for thirdparty enum

namespace Lib {
  enum class Foo {
    Bar = 2,
    Baz = 4
  };
};

and target Qt class

namespace SomeQml {

    class QmlItem : public QObject
    {
        Q_OBJECT
    
        using Foo = Lib::Foo; // its important use without namespace in declaration
    
        Q_PROPERTY(Foo prop MEMBER m_val NOTIFY propChanged)
        ...
        Q_INVOKABLE handleFoo(Foo v);
        ...
    };

}

just call and use on QML side as QmlItem.Bar or QmlItem.Baz as an integer :

qmlRegisterTypeWithEnums<QmlItem, Lib::Foo>("my.pack", 1, 0, "QmlItem");