Restore "Do not create instance of QPlatformIntegration for invalid displays"

This patch is amended version of 67cc8fea106c35c7ca75bf476667d07b3bbf3257,
which was temporary reverted to simplify integration of conflicting
patches. What was amended:

- Dropped the factory interface. It is sufficiently clean to check for
QXcbConnection::isConnected().

Task-number: QTBUG-68859
Change-Id: I810897b3ea20e356fc4d62e6f01231fd287962dc
Reviewed-by: Johan Helsing <johan.helsing@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 7 insertions, 9 deletions

diff --git a/src/plugins/platforms/xcb/qxcbintegration.cpp b/src/plugins/platforms/xcb/qxcbintegration.cpp
index 9a7d193767..ed9e87a036 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.cpp
+++ b/src/plugins/platforms/xcb/qxcbintegration.cpp
@@ -195,14 +195,17 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters, int &argc, char
 
     const int numParameters = parameters.size();
     m_connections.reserve(1 + numParameters / 2);
+
     auto conn = new QXcbConnection(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, displayName);
-    if (conn->isConnected())
-        m_connections << conn;
-    else
+    if (!conn->isConnected()) {
         delete conn;
+        return;
+    }
+    m_connections << conn;
 
+    // ### Qt 6 (QTBUG-52408) remove this multi-connection code path
     for (int i = 0; i < numParameters - 1; i += 2) {
-        qCDebug(lcQpaScreen) << "connecting to additional display: " << parameters.at(i) << parameters.at(i+1);
+        qCDebug(lcQpaXcb) << "connecting to additional display: " << parameters.at(i) << parameters.at(i+1);
         QString display = parameters.at(i) + QLatin1Char(':') + parameters.at(i+1);
         conn = new QXcbConnection(m_nativeInterface.data(), m_canGrab, m_defaultVisualId, display.toLatin1().constData());
         if (conn->isConnected())
@@ -211,11 +214,6 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters, int &argc, char
             delete conn;
     }
 
-    if (m_connections.isEmpty()) {
-        qCritical("Could not connect to any X display.");
-        exit(1);
-    }
-
     m_fontDatabase.reset(new QGenericUnixFontDatabase());
 
 #if QT_CONFIG(xcb_native_painting)