Core: Support for converting user defined QVariant types.

This patchs allows the user to convert defined QMetaType types like
MyType to be converted by using e.g. QVariant::toString(), mapping to
MyType::toString(). Also all the other QVariant::toXYZ() methods are
supported so far.

The patch adds static methods QMetaType::registerConverter supporting:
- implicit convertion
- conversion using member method of source type
- conversion using unary functor

Change-Id: I4f1db83d9c78bcc9df5c42f82f95cce0480cdcc3
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Christoph Schleifenbaum <christoph.schleifenbaum@kdab.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

src/corelib/kernel/qmetatype.cpp

@@ -420,6 +420,49 @@ public:
     int alias;
 };
 
+class QMetaTypeConversionRegistry
+{
+public:
+    typedef QPair<int, int> Key;
+
+    ~QMetaTypeConversionRegistry()
+    {
+        const QWriteLocker locker(&lock);
+        Q_FOREACH (QtPrivate::AbstractConverterFunction *f, map)
+            f->destroy(f);
+        map.clear();
+    }
+
+    bool contains(int from, int to) const
+    {
+        const Key k(from, to);
+        const QReadLocker locker(&lock);
+        return map.contains(k);
+    }
+
+    bool insertIfNotContains(int from, int to, QtPrivate::AbstractConverterFunction *f)
+    {
+        const Key k(from, to);
+        const QWriteLocker locker(&lock);
+        QtPrivate::AbstractConverterFunction* &fun = map[k];
+        if (fun != 0)
+            return false;
+        fun = f;
+        return true;
+    }
+
+    QtPrivate::AbstractConverterFunction *function(int from, int to) const
+    {
+        const Key k(from, to);
+        const QReadLocker locker(&lock);
+        return map.value(k, 0);
+    }
+
+private:
+    mutable QReadWriteLock lock;
+    QHash<Key, QtPrivate::AbstractConverterFunction *> map;
+};
+
 namespace
 {
 union CheckThatItIsPod
@@ -431,6 +474,85 @@ union CheckThatItIsPod
 Q_DECLARE_TYPEINFO(QCustomTypeInfo, Q_MOVABLE_TYPE);
 Q_GLOBAL_STATIC(QVector<QCustomTypeInfo>, customTypes)
 Q_GLOBAL_STATIC(QReadWriteLock, customTypesLock)
+Q_GLOBAL_STATIC(QMetaTypeConversionRegistry, customTypesConversionRegistry)
+
+/*!
+    \fn bool QMetaType::registerConverter()
+    \since 5.1
+    Registers the possibility of an implicit conversion from type From to type To in the meta
+    type system. Returns true if the registration succeeded, otherwise false.
+*/
+
+/*!
+    \fn bool QMetaType::registerConverter(MemberFunction function)
+    \since 5.1
+    \overload
+    Registers a method \a function like To From::function() const as converter from type From
+    to type To in the meta type system. Returns true if the registration succeeded, otherwise false.
+*/
+
+/*!
+    \fn bool QMetaType::registerConverter(MemberFunctionOk function)
+    \since 5.1
+    \overload
+    Registers a method \a function like To From::function(bool *ok) const as converter from type From
+    to type To in the meta type system. Returns true if the registration succeeded, otherwise false.
+*/
+
+/*!
+    \fn bool QMetaType::registerConverter(UnaryFunction function)
+    \since 5.1
+    \overload
+    Registers a unary function object \a function as converter from type From
+    to type To in the meta type system. Returns true if the registration succeeded, otherwise false.
+*/
+
+/*!
+    Registers function \a f as converter function from type id \a from to \a to.
+    If there's already a conversion registered, this does nothing but deleting \a f.
+    Returns true if the registration succeeded, otherwise false.
+    \since 5.1
+    \internal
+*/
+bool QMetaType::registerConverterFunction(QtPrivate::AbstractConverterFunction *f, int from, int to)
+{
+    if (!customTypesConversionRegistry()->insertIfNotContains(from, to, f)) {
+        qWarning("Type conversion already registered from type %s to type %s",
+                 QMetaType::typeName(from), QMetaType::typeName(to));
+        if (f)
+            f->destroy(f);
+        return false;
+    }
+    return true;
+}
+
+/*!
+    Converts the object at \a from from \a fromTypeId to the preallocated space at \a to
+    typed \a toTypeId. Returns true, if the conversion succeeded, otherwise false.
+    \since 5.1
+*/
+bool QMetaType::convert(const void *from, int fromTypeId, void *to, int toTypeId)
+{
+    const QtPrivate::AbstractConverterFunction * const f = customTypesConversionRegistry()->function(fromTypeId, toTypeId);
+    return f && f->convert(f, from, to);
+}
+
+/*!
+    \fn bool QMetaType::hasRegisteredConverterFunction()
+    Returns true, if the meta type system has a registered conversion from type From to type To.
+    \since 5.1
+    \overload
+    */
+
+/*!
+    Returns true, if the meta type system has a registered conversion from meta type id \a fromTypeId
+    to \a toTypeId
+    \since 5.1
+*/
+bool QMetaType::hasRegisteredConverterFunction(int fromTypeId, int toTypeId)
+{
+    return customTypesConversionRegistry()->contains(fromTypeId, toTypeId);
+}
 
 #ifndef QT_NO_DATASTREAM
 /*!

src/corelib/kernel/qmetatype.h

@@ -47,6 +47,7 @@
 #include <QtCore/qbytearray.h>
 #include <QtCore/qvarlengtharray.h>
 #include <QtCore/qisenum.h>
+#include <QtCore/qtypetraits.h>
 #ifndef QT_NO_QOBJECT
 #include <QtCore/qobjectdefs.h>
 #endif
@@ -62,6 +63,11 @@
 
 QT_BEGIN_NAMESPACE
 
+template <typename T>
+struct QMetaTypeId2;
+
+template <typename T>
+inline Q_DECL_CONSTEXPR int qMetaTypeId();
 
 // F is a tuple: (QMetaType::TypeName, QMetaType::TypeNameID, RealType)
 #define QT_FOR_EACH_STATIC_PRIMITIVE_TYPE(F)\
@@ -204,6 +210,105 @@ class QDataStream;
 class QMetaTypeInterface;
 struct QMetaObject;
 
+namespace QtPrivate
+{
+/*!
+    This template is used for implicit conversion from type From to type To.
+    \internal
+*/
+template<typename From, typename To>
+To convertImplicit(const From& from)
+{
+    return from;
+}
+
+struct AbstractConverterFunction
+{
+    typedef bool (*Converter)(const AbstractConverterFunction *, const void *, void*);
+    typedef void (*Destroy)(AbstractConverterFunction *);
+    explicit AbstractConverterFunction(Converter c = 0, Destroy d = 0)
+        : convert(c), destroy(d) {}
+    Q_DISABLE_COPY(AbstractConverterFunction)
+    Converter convert;
+    Destroy destroy;
+};
+
+template<typename From, typename To>
+struct ConverterMemberFunction : public AbstractConverterFunction
+{
+    explicit ConverterMemberFunction(To(From::*function)() const)
+        : AbstractConverterFunction(convert, destroy),
+          m_function(function) {}
+    static bool convert(const AbstractConverterFunction *_this, const void *in, void *out)
+    {
+        const From *f = static_cast<const From *>(in);
+        To *t = static_cast<To *>(out);
+        const ConverterMemberFunction *_typedThis =
+            static_cast<const ConverterMemberFunction *>(_this);
+        *t = (f->*_typedThis->m_function)();
+        return true;
+    }
+
+    static void destroy(AbstractConverterFunction *_this)
+    {
+        delete static_cast<ConverterMemberFunction *>(_this);
+    }
+
+    To(From::* const m_function)() const;
+};
+
+template<typename From, typename To>
+struct ConverterMemberFunctionOk : public AbstractConverterFunction
+{
+    explicit ConverterMemberFunctionOk(To(From::*function)(bool *) const)
+        : AbstractConverterFunction(convert, destroy),
+          m_function(function) {}
+    static bool convert(const AbstractConverterFunction *_this, const void *in, void *out)
+    {
+        const From *f = static_cast<const From *>(in);
+        To *t = static_cast<To *>(out);
+        bool ok = false;
+        const ConverterMemberFunctionOk *_typedThis =
+            static_cast<const ConverterMemberFunctionOk *>(_this);
+        *t = (f->*_typedThis->m_function)(&ok);
+        if (!ok)
+            *t = To();
+        return ok;
+    }
+
+    static void destroy(AbstractConverterFunction *_this)
+    {
+        delete static_cast<ConverterMemberFunctionOk *>(_this);
+    }
+
+    To(From::* const m_function)(bool*) const;
+};
+
+template<typename From, typename To, typename UnaryFunction>
+struct ConverterFunctor : public AbstractConverterFunction
+{
+    explicit ConverterFunctor(UnaryFunction function)
+        : AbstractConverterFunction(convert, destroy),
+          m_function(function) {}
+    static bool convert(const AbstractConverterFunction *_this, const void *in, void *out)
+    {
+        const From *f = static_cast<const From *>(in);
+        To *t = static_cast<To *>(out);
+        const ConverterFunctor *_typedThis =
+            static_cast<const ConverterFunctor *>(_this);
+        *t = _typedThis->m_function(*f);
+        return true;
+    }
+
+    static void destroy(AbstractConverterFunction *_this)
+    {
+        delete static_cast<ConverterFunctor *>(_this);
+    }
+
+    UnaryFunction m_function;
+};
+}
+
 class Q_CORE_EXPORT QMetaType {
     enum ExtensionFlag { NoExtensionFlags,
                          CreateEx = 0x1, DestroyEx = 0x2,
@@ -337,6 +442,70 @@ public:
     inline void destroy(void *data) const;
     inline void *construct(void *where, const void *copy = 0) const;
     inline void destruct(void *data) const;
+
+public:
+    // implicit conversion supported like double -> float
+    template<typename From, typename To>
+    static bool registerConverter()
+    {
+        return registerConverter<From, To>(QtPrivate::convertImplicit<From, To>);
+    }
+
+#ifdef Q_QDOC
+    static bool registerConverter(MemberFunction function);
+    static bool registerConverter(MemberFunctionOk function);
+    static bool registerConverter(UnaryFunction function);
+#else
+    // member function as in "QString QFont::toString() const"
+    template<typename From, typename To>
+    static bool registerConverter(To(From::*function)() const)
+    {
+        Q_STATIC_ASSERT_X((!QMetaTypeId2<To>::IsBuiltIn || !QMetaTypeId2<From>::IsBuiltIn),
+            "QMetaType::registerConverter: At least one of the types must be a custom type.");
+
+        const int fromTypeId = qMetaTypeId<From>();
+        const int toTypeId = qMetaTypeId<To>();
+        return registerConverterFunction(new QtPrivate::ConverterMemberFunction<From, To>(function),
+                                         fromTypeId, toTypeId);
+    }
+
+    // member function as in "double QString::toDouble(bool *ok = 0) const"
+    template<typename From, typename To>
+    static bool registerConverter(To(From::*function)(bool*) const)
+    {
+        Q_STATIC_ASSERT_X((!QMetaTypeId2<To>::IsBuiltIn || !QMetaTypeId2<From>::IsBuiltIn),
+            "QMetaType::registerConverter: At least one of the types must be a custom type.");
+
+        const int fromTypeId = qMetaTypeId<From>();
+        const int toTypeId = qMetaTypeId<To>();
+        return registerConverterFunction(new QtPrivate::ConverterMemberFunctionOk<From, To>(function),
+                                         fromTypeId, toTypeId);
+    }
+
+    // functor or function pointer
+    template<typename From, typename To, typename UnaryFunction>
+    static bool registerConverter(UnaryFunction function)
+    {
+        Q_STATIC_ASSERT_X((!QMetaTypeId2<To>::IsBuiltIn || !QMetaTypeId2<From>::IsBuiltIn),
+            "QMetaType::registerConverter: At least one of the types must be a custom type.");
+
+        const int fromTypeId = qMetaTypeId<From>();
+        const int toTypeId = qMetaTypeId<To>();
+        return registerConverterFunction(new QtPrivate::ConverterFunctor<From, To, UnaryFunction>(function),
+                                        fromTypeId, toTypeId);
+    }
+#endif
+
+    static bool convert(const void *from, int fromTypeId, void *to, int toTypeId);
+
+    template<typename From, typename To>
+    static bool hasRegisteredConverterFunction()
+    {
+        return hasRegisteredConverterFunction(qMetaTypeId<From>(), qMetaTypeId<To>());
+    }
+
+    static bool hasRegisteredConverterFunction(int fromTypeId, int toTypeId);
+
 private:
     static QMetaType typeInfo(const int type);
     inline QMetaType(const ExtensionFlag extensionFlags, const QMetaTypeInterface *info,
@@ -365,6 +534,8 @@ private:
     void *constructExtended(void *where, const void *copy = 0) const;
     void destructExtended(void *data) const;
 
+    static bool registerConverterFunction(QtPrivate::AbstractConverterFunction *f, int from, int to);
+
     Creator m_creator;
     Deleter m_deleter;
     SaveOperator m_saveOp;

src/corelib/kernel/qvariant.cpp

@@ -260,6 +260,16 @@ inline bool qt_convertToBool(const QVariant::Private *const d)
     return !(str == LiteralWrapper("0") || str == LiteralWrapper("false") || str.isEmpty());
 }
 
+/*!
+ \internal
+ Returns the internal data pointer from \a d.
+ */
+
+static const void *constData(const QVariant::Private &d)
+{
+    return d.is_shared ? d.data.shared->ptr : reinterpret_cast<const void *>(&d.data.c);
+}
+
 /*!
  \internal
 
@@ -270,6 +280,14 @@ static bool convert(const QVariant::Private *d, int t, void *result, bool *ok)
     Q_ASSERT(d->type != uint(t));
     Q_ASSERT(result);
 
+    if (d->type >= QMetaType::User || t >= QMetaType::User) {
+        const bool isOk = QMetaType::convert(constData(*d), d->type, result, t);
+        if (ok)
+            *ok = isOk;
+        if (isOk)
+            return true;
+    }
+
     bool dummy;
     if (!ok)
         ok = &dummy;
@@ -842,8 +860,15 @@ static bool customCompare(const QVariant::Private *a, const QVariant::Private *b
     return !memcmp(a_ptr, b_ptr, QMetaType::sizeOf(a->type));
 }
 
-static bool customConvert(const QVariant::Private *, int, void *, bool *ok)
+static bool customConvert(const QVariant::Private *d, int t, void *result, bool *ok)
 {
+    if (d->type >= QMetaType::User || t >= QMetaType::User) {
+        const bool isOk = QMetaType::convert(constData(*d), d->type, result, t);
+        if (ok)
+            *ok = isOk;
+        return isOk;
+    }
+
     if (ok)
         *ok = false;
     return false;
@@ -1933,6 +1958,12 @@ inline T qVariantToHelper(const QVariant::Private &d, const HandlersManager &han
         return *v_cast<T>(&d);
 
     T ret;
+    if (d.type >= QMetaType::User || targetType >= QMetaType::User) {
+        const void * const from = constData(d);
+        if (QMetaType::convert(from, d.type, &ret, targetType))
+            return ret;
+    }
+
     handlerManager[d.type]->convert(&d, targetType, &ret, 0);
     return ret;
 }
@@ -2349,13 +2380,19 @@ template <typename T>
 inline T qNumVariantToHelper(const QVariant::Private &d,
                              const HandlersManager &handlerManager, bool *ok, const T& val)
 {
-    uint t = qMetaTypeId<T>();
+    const uint t = qMetaTypeId<T>();
     if (ok)
         *ok = true;
+
     if (d.type == t)
         return val;
 
     T ret = 0;
+    if ((d.type >= QMetaType::User || t >= QMetaType::User)
+        && QMetaType::convert(&val, d.type, &ret, t)) {
+        return ret;
+    }
+
     if (!handlerManager[d.type]->convert(&d, t, &ret, ok) && ok)
         *ok = false;
     return ret;
@@ -2714,6 +2751,11 @@ static bool canConvertMetaObject(int fromId, int toId, QObject *fromObject)
 */
 bool QVariant::canConvert(int targetTypeId) const
 {
+    if ((d.type >= QMetaType::User || targetTypeId >= QMetaType::User)
+        && QMetaType::hasRegisteredConverterFunction(d.type, targetTypeId)) {
+        return true;
+    }
+
     // TODO Reimplement this function, currently it works but it is a historical mess.
     uint currentType = ((d.type == QMetaType::Float) ? QVariant::Double : d.type);
     if (currentType == QMetaType::SChar || currentType == QMetaType::Char)
@@ -2838,7 +2880,6 @@ bool QVariant::convert(int targetTypeId)
 */
 bool QVariant::convert(const int type, void *ptr) const
 {
-    Q_ASSERT(type < int(QMetaType::User));
     return handlerManager[type]->convert(&d, type, ptr, 0);
 }
 

src/corelib/kernel/qvariant.h

@@ -571,11 +571,9 @@ namespace QtPrivate {
             const int vid = qMetaTypeId<T>();
             if (vid == v.userType())
                 return *reinterpret_cast<const T *>(v.constData());
-            if (vid < int(QMetaType::User)) {
+            T t;
-                T t;
+            if (v.convert(vid, &t))
-                if (v.convert(vid, &t))
+                return t;
-                    return t;
-            }
             return T();
         }
 #ifndef QT_NO_QOBJECT

tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp

@@ -111,6 +111,8 @@ private slots:
     void metaObject();
     void constexprMetaTypeIds();
     void constRefs();
+    void convertCustomType_data();
+    void convertCustomType();
 };
 
 struct Foo { int i; };
@@ -1818,6 +1820,286 @@ void tst_QMetaType::constRefs()
 #endif
 }
 
+struct CustomConvertibleType
+{
+    explicit CustomConvertibleType(const QVariant &foo = QVariant()) : m_foo(foo) {}
+    virtual ~CustomConvertibleType() {}
+    QString toString() const { return QLatin1String("CustomConvertibleType::toString()"); }
+    operator QPoint() const { return QPoint(12, 34); }
+    template<typename To>
+    To convert() const { return s_value.value<To>();}
+    template<typename To>
+    To convertOk(bool *ok) const { *ok = s_ok; return s_value.value<To>();}
+
+    QVariant m_foo;
+    static QVariant s_value;
+    static bool s_ok;
+};
+
+bool operator==(const CustomConvertibleType &lhs, const CustomConvertibleType &rhs)
+{ return lhs.m_foo == rhs.m_foo; }
+bool operator!=(const CustomConvertibleType &lhs, const CustomConvertibleType &rhs)
+{ return !operator==(lhs, rhs); }
+
+QVariant CustomConvertibleType::s_value;
+bool CustomConvertibleType::s_ok = true;
+
+struct CustomConvertibleType2
+{
+    // implicit
+    CustomConvertibleType2(const CustomConvertibleType &t = CustomConvertibleType())
+        : m_foo(t.m_foo) {}
+    virtual ~CustomConvertibleType2() {}
+
+    QVariant m_foo;
+};
+
+bool operator==(const CustomConvertibleType2 &lhs, const CustomConvertibleType2 &rhs)
+{ return lhs.m_foo == rhs.m_foo; }
+bool operator!=(const CustomConvertibleType2 &lhs, const CustomConvertibleType2 &rhs)
+{ return !operator==(lhs, rhs); }
+
+Q_DECLARE_METATYPE(CustomConvertibleType);
+Q_DECLARE_METATYPE(CustomConvertibleType2);
+
+template<typename T, typename U>
+U convert(const T &t)
+{
+    return t;
+}
+
+template<typename From>
+struct ConvertFunctor
+{
+    CustomConvertibleType operator()(const From& f) const
+    {
+        return CustomConvertibleType(QVariant::fromValue(f));
+    }
+};
+
+template<typename From, typename To>
+bool hasRegisteredConverterFunction()
+{
+    return QMetaType::hasRegisteredConverterFunction<From, To>();
+}
+
+template<typename From, typename To>
+void testCustomTypeNotYetConvertible()
+{
+    QVERIFY((!hasRegisteredConverterFunction<From, To>()));
+    QVERIFY((!QVariant::fromValue<From>(From()).canConvert(qMetaTypeId<To>())));
+}
+
+template<typename From, typename To>
+void testCustomTypeConvertible()
+{
+    QVERIFY((hasRegisteredConverterFunction<From, To>()));
+    QVERIFY((QVariant::fromValue<From>(From()).canConvert(qMetaTypeId<To>())));
+}
+
+void customTypeNotYetConvertible()
+{
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QString>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, bool>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, int>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, double>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, float>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QRect>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QRectF>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QPoint>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QPointF>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QSize>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QSizeF>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QLine>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QLineF>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, QChar>();
+    testCustomTypeNotYetConvertible<QString, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<bool, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<int, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<double, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<float, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QRect, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QRectF, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QPoint, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QPointF, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QSize, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QSizeF, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QLine, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QLineF, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<QChar, CustomConvertibleType>();
+    testCustomTypeNotYetConvertible<CustomConvertibleType, CustomConvertibleType2>();
+}
+
+void registerCustomTypeConversions()
+{
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QString>(&CustomConvertibleType::convertOk<QString>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, bool>(&CustomConvertibleType::convert<bool>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, int>(&CustomConvertibleType::convertOk<int>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, double>(&CustomConvertibleType::convert<double>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, float>(&CustomConvertibleType::convertOk<float>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QRect>(&CustomConvertibleType::convert<QRect>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QRectF>(&CustomConvertibleType::convertOk<QRectF>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QPoint>(convert<CustomConvertibleType,QPoint>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QPointF>(&CustomConvertibleType::convertOk<QPointF>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QSize>(&CustomConvertibleType::convert<QSize>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QSizeF>(&CustomConvertibleType::convertOk<QSizeF>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QLine>(&CustomConvertibleType::convert<QLine>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QLineF>(&CustomConvertibleType::convertOk<QLineF>)));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, QChar>(&CustomConvertibleType::convert<QChar>)));
+    QVERIFY((QMetaType::registerConverter<QString, CustomConvertibleType>(ConvertFunctor<QString>())));
+    QVERIFY((QMetaType::registerConverter<bool, CustomConvertibleType>(ConvertFunctor<bool>())));
+    QVERIFY((QMetaType::registerConverter<int, CustomConvertibleType>(ConvertFunctor<int>())));
+    QVERIFY((QMetaType::registerConverter<double, CustomConvertibleType>(ConvertFunctor<double>())));
+    QVERIFY((QMetaType::registerConverter<float, CustomConvertibleType>(ConvertFunctor<float>())));
+    QVERIFY((QMetaType::registerConverter<QRect, CustomConvertibleType>(ConvertFunctor<QRect>())));
+    QVERIFY((QMetaType::registerConverter<QRectF, CustomConvertibleType>(ConvertFunctor<QRectF>())));
+    QVERIFY((QMetaType::registerConverter<QPoint, CustomConvertibleType>(ConvertFunctor<QPoint>())));
+    QVERIFY((QMetaType::registerConverter<QPointF, CustomConvertibleType>(ConvertFunctor<QPointF>())));
+    QVERIFY((QMetaType::registerConverter<QSize, CustomConvertibleType>(ConvertFunctor<QSize>())));
+    QVERIFY((QMetaType::registerConverter<QSizeF, CustomConvertibleType>(ConvertFunctor<QSizeF>())));
+    QVERIFY((QMetaType::registerConverter<QLine, CustomConvertibleType>(ConvertFunctor<QLine>())));
+    QVERIFY((QMetaType::registerConverter<QLineF, CustomConvertibleType>(ConvertFunctor<QLineF>())));
+    QVERIFY((QMetaType::registerConverter<QChar, CustomConvertibleType>(ConvertFunctor<QChar>())));
+    QVERIFY((QMetaType::registerConverter<CustomConvertibleType, CustomConvertibleType2>()));
+    QTest::ignoreMessage(QtWarningMsg, "Type conversion already registered from type CustomConvertibleType to type CustomConvertibleType2");
+    QVERIFY((!QMetaType::registerConverter<CustomConvertibleType, CustomConvertibleType2>()));
+}
+
+void tst_QMetaType::convertCustomType_data()
+{
+    customTypeNotYetConvertible();
+    registerCustomTypeConversions();
+
+    QTest::addColumn<bool>("ok");
+    QTest::addColumn<QString>("testQString");
+    QTest::addColumn<bool>("testBool");
+    QTest::addColumn<int>("testInt");
+    QTest::addColumn<double>("testDouble");
+    QTest::addColumn<float>("testFloat");
+    QTest::addColumn<QRect>("testQRect");
+    QTest::addColumn<QRectF>("testQRectF");
+    QTest::addColumn<QPoint>("testQPoint");
+    QTest::addColumn<QPointF>("testQPointF");
+    QTest::addColumn<QSize>("testQSize");
+    QTest::addColumn<QSizeF>("testQSizeF");
+    QTest::addColumn<QLine>("testQLine");
+    QTest::addColumn<QLineF>("testQLineF");
+    QTest::addColumn<QChar>("testQChar");
+    QTest::addColumn<CustomConvertibleType>("testCustom");
+
+    QTest::newRow("default") << true
+                             << QString::fromLatin1("string") << true << 15
+                             << double(3.14) << float(3.6) << QRect(1, 2, 3, 4)
+                             << QRectF(1.4, 1.9, 10.9, 40.2) << QPoint(12, 34)
+                             << QPointF(9.2, 2.7) << QSize(4, 9) << QSizeF(3.3, 9.8)
+                             << QLine(3, 9, 29, 4) << QLineF(38.9, 28.9, 102.3, 0.0)
+                             << QChar('Q') << CustomConvertibleType(QString::fromLatin1("test"));
+    QTest::newRow("not ok") << false
+                            << QString::fromLatin1("string") << true << 15
+                            << double(3.14) << float(3.6) << QRect(1, 2, 3, 4)
+                            << QRectF(1.4, 1.9, 10.9, 40.2) << QPoint(12, 34)
+                            << QPointF(9.2, 2.7) << QSize(4, 9) << QSizeF(3.3, 9.8)
+                            << QLine(3, 9, 29, 4) << QLineF()
+                            << QChar('Q') << CustomConvertibleType(42);
+}
+
+void tst_QMetaType::convertCustomType()
+{
+    QFETCH(bool, ok);
+    CustomConvertibleType::s_ok = ok;
+
+    CustomConvertibleType t;
+    QVariant v = QVariant::fromValue(t);
+    QFETCH(QString, testQString);
+    CustomConvertibleType::s_value = testQString;
+    QCOMPARE(v.toString(), ok ? testQString : QString());
+    QCOMPARE(v.value<QString>(), ok ? testQString : QString());
+    QVERIFY(CustomConvertibleType::s_value.canConvert<CustomConvertibleType>());
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toString()), testQString);
+
+    QFETCH(bool, testBool);
+    CustomConvertibleType::s_value = testBool;
+    QCOMPARE(v.toBool(), testBool);
+    QCOMPARE(v.value<bool>(), testBool);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toBool()), testBool);
+
+    QFETCH(int, testInt);
+    CustomConvertibleType::s_value = testInt;
+    QCOMPARE(v.toInt(), ok ? testInt : 0);
+    QCOMPARE(v.value<int>(), ok ? testInt : 0);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toInt()), testInt);
+
+    QFETCH(double, testDouble);
+    CustomConvertibleType::s_value = testDouble;
+    QCOMPARE(v.toDouble(), testDouble);
+    QCOMPARE(v.value<double>(), testDouble);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toDouble()), testDouble);
+
+    QFETCH(float, testFloat);
+    CustomConvertibleType::s_value = testFloat;
+    QCOMPARE(v.toFloat(), ok ? testFloat : 0.0);
+    QCOMPARE(v.value<float>(), ok ? testFloat : 0.0);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toFloat()), testFloat);
+
+    QFETCH(QRect, testQRect);
+    CustomConvertibleType::s_value = testQRect;
+    QCOMPARE(v.toRect(), testQRect);
+    QCOMPARE(v.value<QRect>(), testQRect);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toRect()), testQRect);
+
+    QFETCH(QRectF, testQRectF);
+    CustomConvertibleType::s_value = testQRectF;
+    QCOMPARE(v.toRectF(), ok ? testQRectF : QRectF());
+    QCOMPARE(v.value<QRectF>(), ok ? testQRectF : QRectF());
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toRectF()), testQRectF);
+
+    QFETCH(QPoint, testQPoint);
+    CustomConvertibleType::s_value = testQPoint;
+    QCOMPARE(v.toPoint(), testQPoint);
+    QCOMPARE(v.value<QPoint>(), testQPoint);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toPoint()), testQPoint);
+
+    QFETCH(QPointF, testQPointF);
+    CustomConvertibleType::s_value = testQPointF;
+    QCOMPARE(v.toPointF(), ok ? testQPointF : QPointF());
+    QCOMPARE(v.value<QPointF>(), ok ? testQPointF : QPointF());
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toPointF()), testQPointF);
+
+    QFETCH(QSize, testQSize);
+    CustomConvertibleType::s_value = testQSize;
+    QCOMPARE(v.toSize(), testQSize);
+    QCOMPARE(v.value<QSize>(), testQSize);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toSize()), testQSize);
+
+    QFETCH(QSizeF, testQSizeF);
+    CustomConvertibleType::s_value = testQSizeF;
+    QCOMPARE(v.toSizeF(), ok ? testQSizeF : QSizeF());
+    QCOMPARE(v.value<QSizeF>(), ok ? testQSizeF : QSizeF());
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toSizeF()), testQSizeF);
+
+    QFETCH(QLine, testQLine);
+    CustomConvertibleType::s_value = testQLine;
+    QCOMPARE(v.toLine(), testQLine);
+    QCOMPARE(v.value<QLine>(), testQLine);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toLine()), testQLine);
+
+    QFETCH(QLineF, testQLineF);
+    CustomConvertibleType::s_value = testQLineF;
+    QCOMPARE(v.toLineF(), ok ? testQLineF : QLineF());
+    QCOMPARE(v.value<QLineF>(), ok ? testQLineF : QLineF());
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toLineF()), testQLineF);
+
+    QFETCH(QChar, testQChar);
+    CustomConvertibleType::s_value = testQChar;
+    QCOMPARE(v.toChar(), testQChar);
+    QCOMPARE((CustomConvertibleType::s_value.value<CustomConvertibleType>().m_foo.toChar()), testQChar);
+
+    QFETCH(CustomConvertibleType, testCustom);
+    v = QVariant::fromValue(testCustom);
+    QVERIFY(v.canConvert(::qMetaTypeId<CustomConvertibleType2>()));
+    QCOMPARE(v.value<CustomConvertibleType2>().m_foo, testCustom.m_foo);
+}
+
 // Compile-time test, it should be possible to register function pointer types
 class Undefined;