Expose input device group on DBus

This is useful to combine tablet pen and pad devices into one logical device

src/backends/libinput/device.cpp

@@ -17,6 +17,7 @@
 #include "mousebuttons.h"
 #include "pointer_input.h"
 
+#include <QCryptographicHash>
 #include <QDBusArgument>
 #include <QDBusConnection>
 #include <QDBusMetaType>
@@ -360,6 +361,9 @@ Device::Device(libinput_device *device, QObject *parent)
         m_calibrationMatrix = m_defaultCalibrationMatrix;
     }
 
+    libinput_device_group *group = libinput_device_get_device_group(device);
+    m_deviceGroupId = QCryptographicHash::hash(QString::asprintf("%p", group).toLatin1(), QCryptographicHash::Sha1).toBase64();
+
     qDBusRegisterMetaType<QMatrix4x4>();
 
     QDBusConnection::sessionBus().registerObject(QStringLiteral("/org/kde/KWin/InputDevice/") + m_sysName,

src/backends/libinput/device.h

@@ -143,6 +143,7 @@ class KWIN_EXPORT Device : public InputDevice
     Q_PROPERTY(QRectF outputArea READ outputArea WRITE setOutputArea NOTIFY outputAreaChanged)
     Q_PROPERTY(bool defaultMapToWorkspace READ defaultMapToWorkspace CONSTANT)
     Q_PROPERTY(bool mapToWorkspace READ isMapToWorkspace WRITE setMapToWorkspace NOTIFY mapToWorkspaceChanged)
+    Q_PROPERTY(QString deviceGroupId READ deviceGroupId CONSTANT)
 
 public:
     explicit Device(libinput_device *device, QObject *parent = nullptr);
@@ -645,6 +646,11 @@ public:
 
     void setMapToWorkspace(bool mapToWorkspace);
 
+    QString deviceGroupId() const
+    {
+        return m_deviceGroupId;
+    }
+
     /**
      * Gets the Device for @p native. @c null if there is no Device for @p native.
      */
@@ -759,6 +765,7 @@ private:
     LEDs m_leds;
     QRectF m_outputArea = QRectF(0, 0, 1, 1);
     bool m_mapToWorkspace = false;
+    QString m_deviceGroupId;
 };
 
 }