Add native interface for X11 application, exposing display and connection

The major use-case of the now private QX11Info from Qt X11 Extras was
getting hold of the Xlib display and XCB connection, for example in KDE:

  https://lxr.kde.org/search?%21v=kf5-qt5&_filestring=&_string=QX11Info

A new native interface for QGuiApplication has now been added that
exposes these two properties, e.g.:

  if (auto *x11App = app.nativeInterface<QX11Application>())
      qDebug() << x11App->display() << x11App->connection();

To avoid type clashes one of the enum values of QXcbNativeInterface's
ResourceType had to be renamed.

Pick-to: 6.2
Task-number: QTBUG-93633
Change-Id: I2e366a2bb88bd3965ac6172ad000ae32209f43e7
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 90 insertions, 0 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index e966d7962f..55a7c8027b 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -4208,8 +4208,22 @@ QInputDeviceManager *QGuiApplicationPrivate::inputDeviceManager()
     return m_inputDeviceManager;
 }
 
+/*!
+    \fn template <typename QNativeInterface> QNativeInterface *QGuiApplication::nativeInterface() const
+
+    Returns a native interface of the given type for the application.
+
+    This function provides access to platform specific functionality
+    of QGuiApplication, as defined in the QNativeInterface namespace:
+
+    \annotatedlist native-interfaces-qguiapplication
+
+    If the requested interface is not available a \nullptr is returned.
+ */
+
 void *QGuiApplication::resolveInterface(const char *name, int revision) const
 {
+    using namespace QNativeInterface;
     using namespace QNativeInterface::Private;
 
     auto *platformIntegration = QGuiApplicationPrivate::platformIntegration();
@@ -4218,6 +4232,9 @@ void *QGuiApplication::resolveInterface(const char *name, int revision) const
 #if defined(Q_OS_WIN)
     QT_NATIVE_INTERFACE_RETURN_IF(QWindowsApplication, platformIntegration);
 #endif
+#if QT_CONFIG(xcb)
+    QT_NATIVE_INTERFACE_RETURN_IF(QX11Application, platformNativeInterface());
+#endif
 
     return QCoreApplication::resolveInterface(name, revision);
 }
diff --git a/src/gui/kernel/qguiapplication.h b/src/gui/kernel/qguiapplication.h
index 795a88f2b0..3d4534aabf 100644
--- a/src/gui/kernel/qguiapplication.h
+++ b/src/gui/kernel/qguiapplication.h
@@ -219,4 +219,6 @@ private:
 
 QT_END_NAMESPACE
 
+#include <QtGui/qguiapplication_platform.h>
+
 #endif // QGUIAPPLICATION_H
diff --git a/src/gui/kernel/qguiapplication_platform.h b/src/gui/kernel/qguiapplication_platform.h
new file mode 100644
index 0000000000..66cdf10814
--- /dev/null
+++ b/src/gui/kernel/qguiapplication_platform.h
@@ -0,0 +1,71 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QGUIAPPLICATION_PLATFORM_H
+#define QGUIAPPLICATION_PLATFORM_H
+
+#include <QtGui/qtguiglobal.h>
+
+#include <QtCore/qnativeinterface.h>
+#include <QtGui/qguiapplication.h>
+
+#if QT_CONFIG(xcb)
+typedef struct _XDisplay Display;
+struct xcb_connection_t;
+#endif
+
+QT_BEGIN_NAMESPACE
+
+namespace QNativeInterface
+{
+
+#if QT_CONFIG(xcb) || defined(Q_CLANG_QDOC)
+struct Q_GUI_EXPORT QX11Application
+{
+    QT_DECLARE_NATIVE_INTERFACE(QX11Application, 1, QGuiApplication)
+    virtual Display *display() const = 0;
+    virtual xcb_connection_t *connection() const = 0;
+};
+#endif
+
+} // QNativeInterface
+
+QT_END_NAMESPACE
+
+#endif // QGUIAPPLICATION_PLATFORM_H