Make QDebug operator<< polymorphic for QPointingDevice

At least it will look polymorphic by doing dispatch internally.
Adding pointingDeviceType avoids the need for qobject_cast,
and will probably also be useful in other contexts.

Change-Id: I3b6d13765bdf3add9a8208de6f0e98018e40cc42
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

src/gui/kernel/qinputdevice.cpp

@@ -39,6 +39,7 @@
 
 #include "qinputdevice.h"
 #include "qinputdevice_p.h"
+#include "qpointingdevice.h"
 #include <QCoreApplication>
 #include <QDebug>
 #include <QLoggingCategory>
@@ -278,6 +279,9 @@ bool QInputDevice::operator==(const QInputDevice &other) const
 #ifndef QT_NO_DEBUG_STREAM
 QDebug operator<<(QDebug debug, const QInputDevice *device)
 {
+    const QInputDevicePrivate *d = QInputDevicePrivate::get(device);
+    if (d->pointingDeviceType)
+        return operator<<(debug, static_cast<const QPointingDevice *>(device));
     QDebugStateSaver saver(debug);
     debug.nospace();
     debug.noquote();

src/gui/kernel/qinputdevice_p.h

@@ -64,7 +64,8 @@ public:
     QInputDevicePrivate(const QString &name, qint64 id, QInputDevice::DeviceType type,
                         QInputDevice::Capabilities caps = QInputDevice::Capability::None,
                         const QString &seatName = QString())
-      : name(name), seatName(seatName), id(id), capabilities(caps), deviceType(type)
+      : name(name), seatName(seatName), id(id), capabilities(caps),
+        deviceType(type), pointingDeviceType(false)
     {
         // if the platform doesn't provide device IDs, make one up,
         // but try to avoid clashing with OS-provided 32-bit IDs
@@ -81,6 +82,7 @@ public:
     qint64 id = 0;
     qint32 capabilities = static_cast<qint32>(QInputDevice::Capability::None);
     QInputDevice::DeviceType deviceType = QInputDevice::DeviceType::Unknown;
+    qint16 pointingDeviceType : 1; // actually bool, but pack with deviceType
 
     static void registerDevice(const QInputDevice *dev);
     static void unregisterDevice(const QInputDevice *dev);

src/gui/kernel/qpointingdevice_p.h

@@ -70,6 +70,7 @@ public:
         maximumTouchPoints(qint8(maxPoints)), buttonCount(qint8(buttonCount)),
         pointerType(pType)
     {
+        pointingDeviceType = true;
     }
 
     void * extra = nullptr; // QPA plugins can store platform-specific stuff here