QObject: simplify part of connection logic

We do not require anymore that the metatypes are declared beforehand,
but can instead simply use QMetaType::fromType<T>().id().
This allows us to remove the templates containing the "metatype is
declared" validation logic.

Change-Id: I0b74c72643a233335689074091a38648f3e4f853
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/kernel/qobject_impl.h

@@ -56,23 +56,10 @@ namespace QtPrivate {
         Logic to statically generate the array of qMetaTypeId
         ConnectionTypes<FunctionPointer<Signal>::Arguments>::types() returns an array
         of int that is suitable for the types arguments of the connection functions.
-
-        The array only exist of all the types are declared as a metatype
-        (detected using the TypesAreDeclaredMetaType helper struct)
-        If one of the type is not declared, the function return 0 and the signal
-        cannot be used in queued connection.
     */
-    template <typename ArgList> struct TypesAreDeclaredMetaType { enum { Value = false }; };
-    template <> struct TypesAreDeclaredMetaType<List<>> { enum { Value = true }; };
-    template <typename Arg, typename... Tail> struct TypesAreDeclaredMetaType<List<Arg, Tail...> >
-    { enum { Value = QMetaTypeId2<Arg>::Defined && TypesAreDeclaredMetaType<List<Tail...>>::Value }; };
-
-    template <typename ArgList, bool Declared = TypesAreDeclaredMetaType<ArgList>::Value > struct ConnectionTypes
-    { static const int *types() { return nullptr; } };
-    template <> struct ConnectionTypes<List<>, true>
-    { static const int *types() { return nullptr; } };
-    template <typename... Args> struct ConnectionTypes<List<Args...>, true>
-    { static const int *types() { static const int t[sizeof...(Args) + 1] = { (QtPrivate::QMetaTypeIdHelper<Args>::qt_metatype_id())..., 0 }; return t; } };
+    template <typename T> struct ConnectionTypes;
+    template <typename... Args> struct ConnectionTypes<List<Args...>>
+    { static const int *types() { static const int t[sizeof...(Args) + 1] = { QMetaType::fromType<Args>().id()..., 0 }; return t; } };
 
     // implementation of QSlotObjectBase for which the slot is a static function
     // Args and R are the List of arguments and the return type of the signal to which the slot is connected.