xwayland: Replace criticalError() signal with a less fatal signal

If the Xwayland executable can't be found, the whole session will die
because a criticalError() signal will be emitted.

This change replaces the criticalError() signal with a less severe
signal.

If the errorOccurred() signal has been emitted during the startup
sequence, kwin won't die and will just continue with spawning the
session process.

autotests/integration/kwin_wayland_test.cpp

@@ -151,6 +151,7 @@ void WaylandTestApplication::continueStartupWithScreens()
 void WaylandTestApplication::finalizeStartup()
 {
     if (m_xwayland) {
+        disconnect(m_xwayland, &Xwl::Xwayland::errorOccurred, this, &WaylandTestApplication::finalizeStartup);
         disconnect(m_xwayland, &Xwl::Xwayland::started, this, &WaylandTestApplication::finalizeStartup);
     }
     notifyStarted();
@@ -172,12 +173,7 @@ void WaylandTestApplication::continueStartupWithScene()
     }
 
     m_xwayland = new Xwl::Xwayland(this);
-    connect(m_xwayland, &Xwl::Xwayland::criticalError, this, [](int code) {
+    connect(m_xwayland, &Xwl::Xwayland::errorOccurred, this, &WaylandTestApplication::finalizeStartup);
-        // we currently exit on Xwayland errors always directly
-        // TODO: restart Xwayland
-        std::cerr << "Xwayland had a critical error. Going to exit now." << std::endl;
-        exit(code);
-    });
     connect(m_xwayland, &Xwl::Xwayland::started, this, &WaylandTestApplication::finalizeStartup);
     m_xwayland->start();
 }

main_wayland.cpp

@@ -180,6 +180,7 @@ void ApplicationWayland::continueStartupWithScreens()
 void ApplicationWayland::finalizeStartup()
 {
     if (m_xwayland) {
+        disconnect(m_xwayland, &Xwl::Xwayland::errorOccurred, this, &ApplicationWayland::finalizeStartup);
         disconnect(m_xwayland, &Xwl::Xwayland::started, this, &ApplicationWayland::finalizeStartup);
     }
     startSession();
@@ -203,12 +204,7 @@ void ApplicationWayland::continueStartupWithScene()
     }
 
     m_xwayland = new Xwl::Xwayland(this);
-    connect(m_xwayland, &Xwl::Xwayland::criticalError, this, [](int code) {
+    connect(m_xwayland, &Xwl::Xwayland::errorOccurred, this, &ApplicationWayland::finalizeStartup);
-        // we currently exit on Xwayland errors always directly
-        // TODO: restart Xwayland
-        std::cerr << "Xwayland had a critical error. Going to exit now." << std::endl;
-        exit(code);
-    });
     connect(m_xwayland, &Xwl::Xwayland::started, this, &ApplicationWayland::finalizeStartup);
     m_xwayland->start();
 }

xwl/xwayland.cpp

@@ -91,32 +91,32 @@ void Xwayland::start()
     int pipeFds[2];
     if (pipe(pipeFds) != 0) {
         std::cerr << "FATAL ERROR failed to create pipe to start Xwayland " << std::endl;
-        Q_EMIT criticalError(1);
+        emit errorOccurred();
         return;
     }
     int sx[2];
     if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sx) < 0) {
         std::cerr << "FATAL ERROR: failed to open socket to open XCB connection" << std::endl;
-        Q_EMIT criticalError(1);
+        emit errorOccurred();
         return;
     }
     int fd = dup(sx[1]);
     if (fd < 0) {
         std::cerr << "FATAL ERROR: failed to open socket to open XCB connection" << std::endl;
-        Q_EMIT criticalError(20);
+        emit errorOccurred();
         return;
     }
 
     const int waylandSocket = waylandServer()->createXWaylandConnection();
     if (waylandSocket == -1) {
         std::cerr << "FATAL ERROR: failed to open socket for Xwayland" << std::endl;
-        Q_EMIT criticalError(1);
+        emit errorOccurred();
         return;
     }
     const int wlfd = dup(waylandSocket);
     if (wlfd < 0) {
         std::cerr << "FATAL ERROR: failed to open socket for Xwayland" << std::endl;
-        Q_EMIT criticalError(20);
+        emit errorOccurred();
         return;
     }
 
@@ -279,7 +279,6 @@ void Xwayland::handleXwaylandError(QProcess::ProcessError error)
     switch (error) {
     case QProcess::FailedToStart:
         qCWarning(KWIN_XWL) << "Xwayland process failed to start";
-        emit criticalError(1);
         return;
     case QProcess::Crashed:
         qCWarning(KWIN_XWL) << "Xwayland process crashed";
@@ -295,6 +294,7 @@ void Xwayland::handleXwaylandError(QProcess::ProcessError error)
         qCWarning(KWIN_XWL) << "An unknown error has occurred in Xwayland";
         break;
     }
+    emit errorOccurred();
 }
 
 bool Xwayland::createX11Connection()
@@ -353,8 +353,7 @@ void Xwayland::destroyX11Connection()
 void Xwayland::continueStartupWithX()
 {
     if (!createX11Connection()) {
-        // about to quit
+        emit errorOccurred();
-        Q_EMIT criticalError(1);
         return;
     }
 

xwl/xwayland.h

@@ -40,7 +40,7 @@ public Q_SLOTS:
      * Starts the Xwayland server.
      *
      * This method will spawn an Xwayland process and will establish a new XCB connection to it.
-     * If a fatal error has occurred during the startup, the criticalError() signal is going to
+     * If an error has occurred during the startup, the errorOccurred() signal is going to
      * be emitted. If the Xwayland server has started successfully, the started() signal will be
      * emitted.
      *
@@ -72,7 +72,10 @@ Q_SIGNALS:
      * ready to accept and manage X11 clients.
      */
     void started();
-    void criticalError(int code);
+    /**
+     * This signal is emitted when an error occurs with the Xwayland server.
+     */
+    void errorOccurred();
 
 private Q_SLOTS:
     void dispatchEvents();