The code below compiles without any warnings/errors. However,

• QMetaEnum::fromType<NSX:EnumX>.valueToKey(NSX::Foo) returns the correct enum string
• QMetaEnum::fromType<NSY:EnumY>.valueToKey(NSY::Foo) returns an empty string

namespace NSX {
    enum EnumX { Foo, Bar };
    Q_NAMESPACE
    Q_ENUM_NS(EnumX)
}


namespace NSY { // Original definition of NSY
    enum EnumY { Foo, Bar };
}

namespace NSY { // Extension of NSY
    Q_NAMESPACE
    Q_ENUM_NS(EnumY)
}

Suggestions

Ideally, Q_NAMESPACE and Q_ENUM_NS() would work seamlessly in a namespace extension.

If this is not feasible, moc should at least detect and warn that the implementation is not supported.

Use-case

This could be useful for extending a 3rd-party library's namespace to allow introspection with QMetaObject.