Fix a crash when D-Bus library can't be loaded

In certain sandboxes, we have libQtDBus, but not D-Bus. QtDBus shouldn't
crash in that case, but return non-working QDBusConnection instances
instead.

Change-Id: Ia4ac78d1197bae50cde0cf07e6fc66fc25b85011
Reviewed-on: http://codereview.qt.nokia.com/1319
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Robert Griebl <robert.griebl@nokia.com>

src/dbus/qdbus_symbols.cpp

@@ -62,6 +62,12 @@ void qdbus_unloadLibDBus()
 
 bool qdbus_loadLibDBus()
 {
+#ifdef QT_BUILD_INTERNAL
+    // this is to simulate a library load failure for our autotest suite.
+    if (!qgetenv("QT_SIMULATE_DBUS_LIBFAIL").isEmpty())
+        return false;
+#endif
+
     static volatile bool triedToLoadLibrary = false;
 #ifndef QT_NO_THREAD
     QMutexLocker locker(QMutexPool::globalInstanceGet((void *)&qdbus_resolve_me));

src/dbus/qdbusconnection.cpp

@@ -1061,7 +1061,7 @@ public:
         if (!instance) {
             qWarning("QDBusConnection: %s D-Bus connection created before QCoreApplication. Application may misbehave.",
                      type == SessionBus ? "session" : type == SystemBus ? "system" : "generic");
-        } else {
+        } else if (QDBusConnectionPrivate::d(*this)) {
             QDBusConnectionPrivate::d(*this)->moveToThread(instance->thread());
         }
     }

tests/auto/dbus.pro

@@ -3,6 +3,7 @@ SUBDIRS=\
            qdbusabstractadaptor \
            qdbusabstractinterface \
            qdbusconnection \
+           qdbusconnection_no_bus \
            qdbuscontext \
            qdbusinterface \
            qdbuslocalcalls \

tests/auto/qdbusconnection_no_bus/qdbusconnection_no_bus.pro

@@ -0,0 +1,9 @@
+load(qttest_p4)
+QT = core
+
+contains(QT_CONFIG,dbus): {
+    SOURCES += tst_qdbusconnection_no_bus.cpp
+    QT += dbus
+} else {
+    SOURCES += ../qdbusmarshall/dummy.cpp
+}

tests/auto/qdbusconnection_no_bus/tst_qdbusconnection_no_bus.cpp

@@ -0,0 +1,84 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#include <qcoreapplication.h>
+#include <qdebug.h>
+
+#include <QtTest/QtTest>
+#include <QtDBus/QtDBus>
+
+#include <stdlib.h>
+
+/* This test uses an appless main, to ensure that no D-Bus stuff is implicitly done
+   It also sets the magic "QT_SIMULATE_DBUS_LIBFAIL" env variable, that is only available
+   in developer builds. That env variable simulates a D-Bus library load fail.
+
+   In no case should the QDBus module crash because D-Bus libs couldn't be loaded */
+
+class tst_QDBusConnectionNoBus : public QObject
+{
+    Q_OBJECT
+
+public:
+    tst_QDBusConnectionNoBus()
+    {
+        ::setenv("DBUS_SESSION_BUS_ADDRESS", "unix:abstract=/tmp/does_not_exist", 1);
+        ::setenv("QT_SIMULATE_DBUS_LIBFAIL", "1", 1);
+    }
+
+private slots:
+    void connectToBus();
+};
+
+
+void tst_QDBusConnectionNoBus::connectToBus()
+{
+    int argc = 0;
+    QCoreApplication app(argc, 0);
+
+    QDBusConnection con = QDBusConnection::sessionBus();
+
+    QVERIFY(true); // if we didn't crash here, the test passed :)
+}
+
+QTEST_APPLESS_MAIN(tst_QDBusConnectionNoBus)
+
+#include "tst_qdbusconnection_no_bus.moc"
+