Avoid setting the active window to null when there is a FocusIn queued.

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -483,6 +483,11 @@ void QXcbConnection::handleXcbEvent(xcb_generic_event_t *event)
         printXcbEvent("Unhandled XCB event", event);
 }
 
+void QXcbConnection::addPeekFunc(PeekFunc f)
+{
+    m_peekFuncs.append(f);
+}
+
 void QXcbConnection::processXcbEvents()
 {
     while (xcb_generic_event_t *event = xcb_poll_for_event(xcb_connection()))
@@ -498,6 +503,15 @@ void QXcbConnection::processXcbEvents()
         if (!response_type) {
             handleXcbError((xcb_generic_error_t *)event);
         } else {
+            QVector<PeekFunc>::iterator it = m_peekFuncs.begin();
+            while (it != m_peekFuncs.end()) {
+                // These callbacks return true if the event is what they were
+                // waiting for, remove them from the list in that case.
+                if ((*it)(event))
+                    it = m_peekFuncs.erase(it);
+                else
+                    ++it;
+            }
             handleXcbEvent(event);
         }
 
@@ -506,6 +520,12 @@ void QXcbConnection::processXcbEvents()
 
     eventqueue.clear();
 
+    // Indicate with a null event that the event the callbacks are waiting for
+    // is not in the queue currently.
+    Q_FOREACH (PeekFunc f, m_peekFuncs)
+        f(0);
+    m_peekFuncs.clear();
+
     xcb_flush(xcb_connection());
 }
 

src/plugins/platforms/xcb/qxcbconnection.h

@@ -284,6 +284,9 @@ public:
 
     QXcbWindow *platformWindowFromId(xcb_window_t id);
 
+    typedef bool (*PeekFunc)(xcb_generic_event_t *);
+    void addPeekFunc(PeekFunc f);
+
 private slots:
     void processXcbEvents();
 
@@ -335,6 +338,8 @@ private:
     QVector<xcb_generic_event_t *> eventqueue;
 
     WindowMapper m_mapper;
+
+    QVector<PeekFunc> m_peekFuncs;
 };
 
 #define DISPLAY_FROM_XCB(object) ((Display *)(object->connection()->xlib_display()))

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -1087,9 +1087,23 @@ void QXcbWindow::handleFocusInEvent(const xcb_focus_in_event_t *)
     QWindowSystemInterface::handleWindowActivated(window());
 }
 
+static bool focusInPeeker(xcb_generic_event_t *event)
+{
+    if (!event) {
+        // FocusIn event is not in the queue, proceed with FocusOut normally.
+        QWindowSystemInterface::handleWindowActivated(0);
+        return true;
+    }
+    uint response_type = event->response_type & ~0x80;
+    return response_type == XCB_FOCUS_IN;
+}
+
 void QXcbWindow::handleFocusOutEvent(const xcb_focus_out_event_t *)
 {
-    QWindowSystemInterface::handleWindowActivated(0);
+    // Do not set the active window to 0 if there is a FocusIn coming.
+    // There is however no equivalent for XPutBackEvent so register a
+    // callback for QXcbConnection instead.
+    connection()->addPeekFunc(focusInPeeker);
 }
 
 void QXcbWindow::updateSyncRequestCounter()

src/widgets/kernel/qapplication_qpa.cpp

@@ -161,6 +161,8 @@ void QApplicationPrivate::notifyActiveWindowChange(QWindow *previous)
     Q_UNUSED(previous);
     Q_Q(QApplication);
     QWindow *wnd = QGuiApplicationPrivate::active_window;
+    if (inPopupMode()) // some delayed focus event to ignore
+        return;
     QWidget *tlw = qt_tlw_for_window(wnd);
     q->setActiveWindow(tlw);
 }