xcb: remove multi-connection code path

This code was introduced in 2011 as an experimental feature
and have been untested/unmaintained ever since. It's time to
remove it for the following reasons:

- It has never been documented in QGuiApplication under
  "Supported Command Line Options". The intended command
  line was: ./app -platform xcb:address:display

- I am not aware of other toolkits that would provide this
  functionality - connecting to several X displays simultaneously.

- XCB plugin respects the "-display" command line and DISPLAY
  envvar which should be sufficient. So the "workaround" to get
  your window on 2 X displays is:

    ./app -display :0
    ./app -display :1

- There are no JIRA bugs where users would complain that this
  feature does not work. AFAICT it has not worked for years.
  Almost all functions care only about the "default" connection,
  and don't attempt to support multi-connection.

- This will stop confusing people who want to contribute to
  the XCB plugin.

[ChangeLog][Platform Specific Changes][X11] Connecting to multiple
X servers simultaneously within the same application is no longer
supported.

Task-number: QTBUG-52408
Change-Id: I61ce23480702bb89b02c6028fa0986fe63481978
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/plugins/platforms/xcb/qxcbintegration.h b/src/plugins/platforms/xcb/qxcbintegration.h
index 571726c354..a67e79e0b8 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.h
+++ b/src/plugins/platforms/xcb/qxcbintegration.h
@@ -102,8 +102,8 @@ public:
     QPlatformTheme *createPlatformTheme(const QString &name) const override;
     QVariant styleHint(StyleHint hint) const override;
 
-    bool hasDefaultConnection() const { return !m_connections.isEmpty(); }
-    QXcbConnection *defaultConnection() const { return m_connections.first(); }
+    bool hasConnection() const { return m_connection; }
+    QXcbConnection *connection() const { return m_connection; }
 
     QByteArray wmClass() const;
 
@@ -124,7 +124,7 @@ public:
     static QXcbIntegration *instance() { return m_instance; }
 
 private:
-    QList<QXcbConnection *> m_connections;
+    QXcbConnection *m_connection = nullptr;
 
     QScopedPointer<QPlatformFontDatabase> m_fontDatabase;
     QScopedPointer<QXcbNativeInterface> m_nativeInterface;