Add a runtime warning when dummy QtBluetooth backend is running

There have been plenty of bugs where QtBluetooth was compiled
with the dummy backend and the API user reported bugs against it. So far
debug output was not able to identify the dummy backend which made
debugging of customer code more difficult.

This patch prints the name of the backend once shortly after the
application startup. The other backends like Bluez do that already.

Change-Id: I86353ef3c9c99cafac38805f253e20a3ad3e10a5
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@theqtcompany.com>

3 files changed, 111 insertions, 0 deletions

diff --git a/src/bluetooth/dummy/dummy.pri b/src/bluetooth/dummy/dummy.pri
new file mode 100644
index 00000000..49aa076c
--- /dev/null
+++ b/src/bluetooth/dummy/dummy.pri
@@ -0,0 +1,2 @@
+HEADERS += dummy/dummy_helper_p.h
+SOURCES += dummy/dummy_helper.cpp
diff --git a/src/bluetooth/dummy/dummy_helper.cpp b/src/bluetooth/dummy/dummy_helper.cpp
new file mode 100644
index 00000000..fc78ea2f
--- /dev/null
+++ b/src/bluetooth/dummy/dummy_helper.cpp
@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtBluetooth module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** 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 http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://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 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtCore/QGlobalStatic>
+#include <QtCore/QLoggingCategory>
+
+#include "dummy_helper_p.h"
+
+QT_BEGIN_NAMESPACE
+
+Q_DECLARE_LOGGING_CATEGORY(QT_BT)
+
+Q_GLOBAL_STATIC_WITH_ARGS(bool, dummyWarningPrinted, (false))
+
+void printDummyWarning()
+{
+    if (!*dummyWarningPrinted()) {
+        qCWarning(QT_BT) << "Dummy backend running. Qt Bluetooth module is non-functional.";
+        *dummyWarningPrinted() = true;
+    }
+}
+
+QT_END_NAMESPACE
diff --git a/src/bluetooth/dummy/dummy_helper_p.h b/src/bluetooth/dummy/dummy_helper_p.h
new file mode 100644
index 00000000..f548ac36
--- /dev/null
+++ b/src/bluetooth/dummy/dummy_helper_p.h
@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtBluetooth module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** 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 http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://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 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef DUMMY_HELPER_H
+#define DUMMY_HELPER_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include "QtCore/qglobal.h"
+
+QT_BEGIN_NAMESPACE
+
+void printDummyWarning();
+
+QT_END_NAMESPACE
+
+#endif // DUMMY_HELPER_H