C++ QT5.5中qDebug（）的新QFlags帮助程序存在问题

我有以下代码

#include <QDebug>  //Needed for other stuff!!
#include <QDataStream>

class TestClass {
public:
    class SubClass {
    public:
        QString a;
        int b;

        /*
        //Needed for QDataStream but not relevant for the generated error
        friend QDataStream& operator<<(QDataStream& os, SubClass const& f)
        {
            os << f.a;
            os << f.b;
            return os;
        }

        friend QDataStream& operator>>(QDataStream& is, SubClass& f)
        {
            is >> f.a;
            is >> f.b;
            return is;
        }*/

        friend QDataStream& operator<< <SubClass>(QDataStream&, QList<SubClass> const&);
        friend QDataStream& operator>> <SubClass>(QDataStream&, QList<SubClass>&);

    };
};

#包括//其他东西需要的！！
#包括
类TestClass{
公众：
类子类{
公众：
QString a；
int b；
/*
//QDataStream需要，但与生成的错误无关
friend QDataStream&运营商f.a；
is>>f.b；
回报是；
}*/
friend QDataStream&operator>（QDataStream&，QList&）；
};
};

使用qt5.5编译它时会出现以下错误：

/usr/include/qt/QtCore/qflags.h:88: error: invalid application of 'sizeof' to an incomplete type 'TestClass::SubClass'
    Q_STATIC_ASSERT_X((sizeof(Enum) <= sizeof(int)),
                   ^~~~~~~~~~~~
/usr/include/qt/QtCore/qtypetraits.h:478: error: 'TestClass::SubClass' is an incomplete type
    : integral_constant<bool, (T(0) < T(-1))> {};
                               ^
/usr/include/qt/QtCore/qdebug.h:279: in instantiation of template class 'QtPrivate::IsQEnumHelper<QFlags<TestClass::SubClass> >' requested here
    QtPrivate::IsQEnumHelper<T>::Value || QtPrivate::IsQEnumHelper<QFlags<T> >::Value,
                                                     ^
main.cpp:25: while substituting explicitly-specified template arguments into function template 'operator<<'
        friend QDataStream& operator<< <SubClass>(QDataStream&, QList<SubClass> const&);
                            ^

/usr/include/qt/QtCore/qflags.h:88:错误：“sizeof”对不完整类型“TestClass:：SubClass”的应用无效
Q_STATIC_ASSERT_X（（sizeof（Enum）以下（简化代码）生成相同的错误

#include <QDebug>  //Needed to cause the error

class TestClassA {};
class TestClassB {};

template <typename T>
TestClassA& operator<<(TestClassA& s, T& l) {
    Q_UNUSED(l)
    return s;
}

template TestClassA& operator<< <TestClassB>(TestClassA& s, TestClassB& l);

#包含//导致错误所需的
类TestClassA{}；
类TestClassB{}；
模板
TestClassA&operator以下（简化代码）生成相同的错误

#include <QDebug>  //Needed to cause the error

class TestClassA {};
class TestClassB {};

template <typename T>
TestClassA& operator<<(TestClassA& s, T& l) {
    Q_UNUSED(l)
    return s;
}

template TestClassA& operator<< <TestClassB>(TestClassA& s, TestClassB& l);

#包含//导致错误所需的
类TestClassA{}；
类TestClassB{}；
模板
TestClassA&运算符
#include <QDebug>  //Needed to cause the error

class TestClassA {};
class TestClassB {};

template <typename T>
TestClassA& operator<<(TestClassA& s, T& l) {
    Q_UNUSED(l)
    return s;
}

template TestClassA& operator<< <TestClassB>(TestClassA& s, TestClassB& l);