shutdown: Introduce support for KWin closing wayland windows

After ksmserver is done, KWin will now close (or not) open wayland
windows. Since this operation can also cancel the logout, ksmserver
gains a new hook to reset its state. This also means that it cannot
quit itself anymore but needs to be managed by plasma-shutdown.
Using this opportunity the  path for shutdown can be aligned between
X11 and Wayland. In the systemd-managed case we stop graphical-session.target,
otherwise plasma-shutdown quits KWin and ksmserver.
BUG: 461176
FIXED-IN: 6.0

ksmserver/logout.cpp

@@ -427,7 +427,6 @@ void KSMServer::completeKilling()
 void KSMServer::killingCompleted()
 {
     Q_EMIT logoutFinished(true);
-    qApp->quit();
 }
 
 void KSMServer::timeoutQuit()
@@ -509,3 +508,8 @@ void KSMServer::signalSubSessionClosed()
     qCDebug(KSMSERVER) << state;
     Q_EMIT subSessionClosed();
 }
+
+void KSMServer::resetLogout()
+{
+    state = Idle;
+}

ksmserver/org.kde.KSMServerInterface.xml

@@ -36,5 +36,8 @@
         <!-- Performs a logout and closes the session. Returns true if the session was closed successfully, false if cancelled by the user-->
         <arg type="b" direction="out"/>
     </method>
+    <method name="resetLogout">
+      <!-- Called when logout is cancelled -->
+    </method>
   </interface>
 </node>

ksmserver/org.kde.KWin.Session.xml

@@ -22,5 +22,8 @@
     <!-- Shutdown kwin at the end of the session -->
       <method name="quit">
       </method>
+        <method name="closeWaylandWindows">
+          <arg type="b" direction="out" />
+      </method>
    </interface>
 </node>

ksmserver/server.h

@@ -98,6 +98,7 @@ class KSMServer : public QObject, protected QDBusContext
     void restoreSession();
     void setRestoreSession(const QString &sessionName);
     void startDefaultSession();
+    void resetLogout();
 
 Q_SIGNALS:
     void logoutFinished(bool sessionClosed);

startkde/plasma-shutdown/shutdown.cpp

@@ -53,8 +53,33 @@ void Shutdown::startLogout(KWorkSpace::ShutdownType shutdownType)
             return;
         }
         if (closeSessionReply.value()) {
+            ksmServerComplete();
+        } else {
+            logoutCancelled();
+        }
+    });
+}
+
+void Shutdown::ksmServerComplete()
+{
+    OrgKdeKWinSessionInterface kwinInterface(QStringLiteral("org.kde.KWin"), QStringLiteral("/Session"), QDBusConnection::sessionBus());
+    kwinInterface.setTimeout(INT32_MAX);
+    auto reply = kwinInterface.closeWaylandWindows();
+    auto watcher = new QDBusPendingCallWatcher(reply, this);
+    connect(watcher, &QDBusPendingCallWatcher::finished, this, [this](QDBusPendingCallWatcher *watcher) {
+        watcher->deleteLater();
+        OrgKdeKSMServerInterfaceInterface ksmserverIface(QStringLiteral("org.kde.ksmserver"), QStringLiteral("/KSMServer"), QDBusConnection::sessionBus());
+        auto reply = QDBusReply<bool>(*watcher);
+        if (!reply.isValid()) {
+            qCWarning(PLASMA_SESSION) << "KWin failed to complete logout";
+            ksmserverIface.resetLogout();
+            logoutCancelled();
+            return;
+        }
+        if (reply.value()) {
             logoutComplete();
         } else {
+            ksmserverIface.resetLogout();
             logoutCancelled();
         }
     });
@@ -78,6 +103,12 @@ void Shutdown::logoutComplete()
     QDBusReply<QDBusObjectPath> reply = QDBusConnection::sessionBus().call(msg);
 
     if (!reply.isValid()) {
+        auto msg = QDBusMessage::createMethodCall(QStringLiteral("org.kde.ksmserver"),
+                                                  QStringLiteral("/MainApplication"),
+                                                  QStringLiteral("org.qtproject.Qt.QCoreApplication"),
+                                                  QStringLiteral("quit"));
+        QDBusConnection::sessionBus().call(msg);
+
         OrgKdeKWinSessionInterface kwinInterface(QStringLiteral("org.kde.KWin"), QStringLiteral("/Session"), QDBusConnection::sessionBus());
         QDBusPendingReply<> reply = kwinInterface.quit();
         reply.waitForFinished();

startkde/plasma-shutdown/shutdown.h

@@ -22,6 +22,7 @@ class Shutdown : public QObject
 private Q_SLOTS:
     void logoutCancelled();
     void logoutComplete();
+    void ksmServerComplete();
 
 private:
     void startLogout(KWorkSpace::ShutdownType shutdownType);