Fix xrandr primary when the new screen is the connected one

We'd trigger updatePrimary before Xwayland had reacted to the new output
so we wouldn't end up calling xcb_randr_set_output_primary() as
necessary.

BUG: 449099

src/utils/xcbutils.cpp

@@ -364,6 +364,7 @@ Extensions::~Extensions()
 void Extensions::init()
 {
     xcb_connection_t *c = connection();
+    Q_ASSERT(c);
     xcb_prefetch_extension_data(c, &xcb_shape_id);
     xcb_prefetch_extension_data(c, &xcb_randr_id);
     xcb_prefetch_extension_data(c, &xcb_damage_id);

src/xwl/xwayland.cpp

@@ -22,6 +22,7 @@
 #include "utils/xcbutils.h"
 #include "wayland_server.h"
 #include "xwayland_logging.h"
+#include "x11eventfilter.h"
 
 #include "xwaylandsocket.h"
 
@@ -55,6 +56,31 @@ namespace KWin
 namespace Xwl
 {
 
+class XrandrEventFilter : public X11EventFilter
+{
+public:
+    explicit XrandrEventFilter(Xwayland *backend);
+
+    bool event(xcb_generic_event_t *event) override;
+
+private:
+    Xwayland *const m_backend;
+};
+
+XrandrEventFilter::XrandrEventFilter(Xwayland *backend)
+    : X11EventFilter(Xcb::Extensions::self()->randrNotifyEvent())
+    , m_backend(backend)
+{
+}
+
+bool XrandrEventFilter::event(xcb_generic_event_t *event)
+{
+    Q_ASSERT((event->response_type & ~0x80) == Xcb::Extensions::self()->randrNotifyEvent());
+    m_backend->updatePrimary(kwinApp()->platform()->primaryOutput());
+    return false;
+}
+
+
 Xwayland::Xwayland(ApplicationWaylandAbstract *app, QObject *parent)
     : XwaylandInterface(parent)
     , m_app(app)
@@ -221,6 +247,9 @@ void Xwayland::stopInternal()
     Q_ASSERT(m_xwaylandProcess);
     m_app->setClosingX11Connection(true);
 
+    delete m_xrandrEventsFilter;
+    m_xrandrEventsFilter = nullptr;
+
     // If Xwayland has crashed, we must deactivate the socket notifier and ensure that no X11
     // events will be dispatched before blocking; otherwise we will simply hang...
     uninstallSocketNotifier();
@@ -407,6 +436,9 @@ void Xwayland::handleXwaylandReady()
     updatePrimary(kwinApp()->platform()->primaryOutput());
 
     Xcb::sync(); // Trigger possible errors, there's still a chance to abort
+
+    delete m_xrandrEventsFilter;
+    m_xrandrEventsFilter = new XrandrEventFilter(this);
 }
 
 void Xwayland::updatePrimary(AbstractOutput *primaryOutput)

src/xwl/xwayland.h

@@ -26,6 +26,7 @@ class XwaylandSocket;
 
 namespace Xwl
 {
+class XrandrEventFilter;
 
 class KWIN_EXPORT Xwayland : public XwaylandInterface
 {
@@ -113,6 +114,8 @@ private Q_SLOTS:
     void handleSelectionClaimedOwnership();
 
 private:
+    friend class XrandrEventFilter;
+
     void installSocketNotifier();
     void uninstallSocketNotifier();
     void maybeDestroyReadyNotifier();
@@ -143,6 +146,7 @@ private:
     QString m_xAuthority;
 
     int m_crashCount = 0;
+    XrandrEventFilter *m_xrandrEventsFilter = nullptr;
 
     Q_DISABLE_COPY(Xwayland)
 };