Revert "D-Bus system tray: properly check whether StatusNotifierHost available"

This reverts commit 23e9b57e3d261f66168a8a28ccb8e5c886b4841f.

The original commit was made based on a KDE workaround for
libdbusmenu-qt crash, but Qt is not using libdbusmenu-qt, Qt is not
watching for StatusNotifierHost registration and Qt is not capable
to switch backends on the fly leading to tray support being
not detected on Plasma Wayland sessions and falling back to the poor
legacy protocol on X11.

Task-number: QTBUG-94871
Pick-to: 6.5
Change-Id: Ic3e4a9c2d6db00299ed1f2b14043c4b675fb8ccc
Reviewed-by: Dmitry Shachnev <mitya57@gmail.com>
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

4 files changed, 13 insertions, 10 deletions

diff --git a/src/gui/platform/unix/dbusmenu/qdbusmenuconnection.cpp b/src/gui/platform/unix/dbusmenu/qdbusmenuconnection.cpp
index 9391b77f6a..1023b16662 100644
--- a/src/gui/platform/unix/dbusmenu/qdbusmenuconnection.cpp
+++ b/src/gui/platform/unix/dbusmenu/qdbusmenuconnection.cpp
@@ -40,14 +40,14 @@ QDBusMenuConnection::QDBusMenuConnection(QObject *parent, const QString &service
     , m_connection(serviceName.isNull() ? QDBusConnection::sessionBus()
                                         : QDBusConnection::connectToBus(QDBusConnection::SessionBus, serviceName))
     , m_dbusWatcher(new QDBusServiceWatcher(StatusNotifierWatcherService, m_connection, QDBusServiceWatcher::WatchForRegistration, this))
-    , m_statusNotifierHostRegistered(false)
+    , m_watcherRegistered(false)
 {
 #ifndef QT_NO_SYSTEMTRAYICON
-    QDBusInterface systrayHost(StatusNotifierWatcherService, StatusNotifierWatcherPath, StatusNotifierWatcherService, m_connection);
-    if (systrayHost.isValid() && systrayHost.property("IsStatusNotifierHostRegistered").toBool())
-        m_statusNotifierHostRegistered = true;
+    // Start monitoring if any known tray-related services are registered.
+    if (m_connection.interface()->isServiceRegistered(StatusNotifierWatcherService))
+        m_watcherRegistered = true;
     else
-        qCDebug(qLcMenu) << "StatusNotifierHost is not registered";
+        qCDebug(qLcMenu) << "failed to find service" << StatusNotifierWatcherService;
 #endif
 }
 
diff --git a/src/gui/platform/unix/dbusmenu/qdbusmenuconnection_p.h b/src/gui/platform/unix/dbusmenu/qdbusmenuconnection_p.h
index 69713b12bd..37033e2fa3 100644
--- a/src/gui/platform/unix/dbusmenu/qdbusmenuconnection_p.h
+++ b/src/gui/platform/unix/dbusmenu/qdbusmenuconnection_p.h
@@ -39,7 +39,7 @@ public:
     ~QDBusMenuConnection();
     QDBusConnection connection() const { return m_connection; }
     QDBusServiceWatcher *dbusWatcher() const { return m_dbusWatcher; }
-    bool isStatusNotifierHostRegistered() const { return m_statusNotifierHostRegistered; }
+    bool isWatcherRegistered() const { return m_watcherRegistered; }
 #ifndef QT_NO_SYSTEMTRAYICON
     bool registerTrayIconMenu(QDBusTrayIcon *item);
     void unregisterTrayIconMenu(QDBusTrayIcon *item);
@@ -60,7 +60,7 @@ private:
     QString m_serviceName;
     QDBusConnection m_connection;
     QDBusServiceWatcher *m_dbusWatcher;
-    bool m_statusNotifierHostRegistered;
+    bool m_watcherRegistered;
 };
 
 QT_END_NAMESPACE
diff --git a/src/gui/platform/unix/dbustray/qdbustrayicon.cpp b/src/gui/platform/unix/dbustray/qdbustrayicon.cpp
index 18334e5715..5be223b510 100644
--- a/src/gui/platform/unix/dbustray/qdbustrayicon.cpp
+++ b/src/gui/platform/unix/dbustray/qdbustrayicon.cpp
@@ -331,8 +331,11 @@ void QDBusTrayIcon::notificationClosed(uint id, uint reason)
 bool QDBusTrayIcon::isSystemTrayAvailable() const
 {
     QDBusMenuConnection * conn = const_cast<QDBusTrayIcon *>(this)->dBusConnection();
-    qCDebug(qLcTray) << conn->isStatusNotifierHostRegistered();
-    return conn->isStatusNotifierHostRegistered();
+
+    // If the KDE watcher service is registered, we must be on a desktop
+    // where a StatusNotifier-conforming system tray exists.
+    qCDebug(qLcTray) << conn->isWatcherRegistered();
+    return conn->isWatcherRegistered();
 }
 
 QT_END_NAMESPACE
diff --git a/src/gui/platform/unix/qgenericunixthemes.cpp b/src/gui/platform/unix/qgenericunixthemes.cpp
index d767767893..cdc179ad2f 100644
--- a/src/gui/platform/unix/qgenericunixthemes.cpp
+++ b/src/gui/platform/unix/qgenericunixthemes.cpp
@@ -77,7 +77,7 @@ static bool isDBusTrayAvailable() {
     static bool dbusTrayAvailableKnown = false;
     if (!dbusTrayAvailableKnown) {
         QDBusMenuConnection conn;
-        if (conn.isStatusNotifierHostRegistered())
+        if (conn.isWatcherRegistered())
             dbusTrayAvailable = true;
         dbusTrayAvailableKnown = true;
         qCDebug(qLcTray) << "D-Bus tray available:" << dbusTrayAvailable;