Don't increase the reference count if dynamic_cast failed

If the dynamic_cast failed in QSharedPointer::dynamicCast or
qSharedPointerDynamicCast, we should avoid creating the QSharedPointer
that shares the weak and strong reference counts. In Qt 5, this does
not imply a leak since the original pointer is stored internally for
deletion. In Qt 4 it implies a leak under certain circumstances, which
this change fixes.

Task-number: QTBUG-28924
Change-Id: Id2de140de4cf676461e14b201ad250c53666b79d
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/tools/qsharedpointer_impl.h

@@ -786,6 +786,8 @@ template <class X, class T>
 Q_INLINE_TEMPLATE QSharedPointer<X> qSharedPointerDynamicCast(const QSharedPointer<T> &src)
 {
     register X *ptr = dynamic_cast<X *>(src.data()); // if you get an error in this line, the cast is invalid
+    if (!ptr)
+        return QSharedPointer<X>();
     return QtSharedPointer::copyAndSetPointer(ptr, src);
 }
 template <class X, class T>

tests/auto/corelib/tools/qsharedpointer/nontracked.cpp

@@ -0,0 +1,116 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 Intel Corporation.
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the test suite 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/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 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, Digia gives you certain additional
+** rights.  These rights are described in the Digia 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.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*
+ * This file exists because tst_qsharedpointer.cpp is compiled with
+ * QT_SHAREDPOINTER_TRACK_POINTERS. That changes some behavior.
+ *
+ * Note that most of these tests may yield false-positives in debug mode, but
+ * they should not yield false negatives. That is, they may report PASS when
+ * they are failing, but they should not produce FAILs.
+ *
+ * The reason for that is because of C++'s One Definition Rule: the macro
+ * changes some functions and, in debug mode, they will not be inlined. At link
+ * time, the two functions would be merged.
+ */
+
+#include <qsharedpointer.h>
+#include <QtTest>
+
+#include "nontracked.h"
+
+// We can't name our classes Data and DerivedData: those are in tst_qsharedpointer.cpp
+namespace NonTracked {
+
+class Data
+{
+public:
+    static int destructorCounter;
+    static int generationCounter;
+    int generation;
+
+    Data() : generation(++generationCounter)
+    { }
+
+    virtual ~Data()
+    {
+        if (generation <= 0)
+            qFatal("tst_qsharedpointer: Double deletion!");
+        generation = 0;
+        ++destructorCounter;
+    }
+};
+int Data::generationCounter = 0;
+int Data::destructorCounter = 0;
+
+class DerivedData: public Data
+{
+public:
+    static int derivedDestructorCounter;
+    int moreData;
+    DerivedData() : moreData(0) { }
+    ~DerivedData() { ++derivedDestructorCounter; }
+};
+int DerivedData::derivedDestructorCounter = 0;
+
+
+#ifndef QTEST_NO_RTTI
+void dynamicCastFailureNoLeak()
+{
+    Data::destructorCounter = DerivedData::derivedDestructorCounter = 0;
+
+    // see QTBUG-28924
+    QSharedPointer<Data> a(new Data);
+    QSharedPointer<DerivedData> b = a.dynamicCast<DerivedData>();
+    QVERIFY(!a.isNull());
+    QVERIFY(b.isNull());
+
+    a.clear();
+    b.clear();
+    QVERIFY(a.isNull());
+
+    // verify that the destructors were called
+    QCOMPARE(Data::destructorCounter, 1);
+    QCOMPARE(DerivedData::derivedDestructorCounter, 0);
+}
+
+#endif
+} // namespace NonTracked

tests/auto/corelib/tools/qsharedpointer/nontracked.h

@@ -0,0 +1,49 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 Intel Corporation.
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the test suite 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/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 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, Digia gives you certain additional
+** rights.  These rights are described in the Digia 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.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef NONTRACKED_H
+#define NONTRACKED_H
+
+namespace NonTracked {
+void dynamicCastFailureNoLeak();
+}
+
+#endif // NONTRACKED_H

tests/auto/corelib/tools/qsharedpointer/qsharedpointer.pro

@@ -5,9 +5,11 @@ QT = core testlib
 
 SOURCES = tst_qsharedpointer.cpp \
     forwarddeclared.cpp \
+    nontracked.cpp \
     wrapper.cpp
 
 HEADERS = forwarddeclared.h \
+    nontracked.h \
     wrapper.h
 
 TESTDATA += forwarddeclared.cpp forwarddeclared.h

tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp

@@ -50,6 +50,7 @@
 
 #include "externaltests.h"
 #include "forwarddeclared.h"
+#include "nontracked.h"
 #include "wrapper.h"
 
 #include <stdlib.h>
@@ -88,6 +89,7 @@ private slots:
     void dynamicCastDifferentPointers();
     void dynamicCastVirtualBase();
     void dynamicCastFailure();
+    void dynamicCastFailureNoLeak();
 #endif
     void constCorrectness();
     void customDeleter();
@@ -1066,6 +1068,11 @@ void tst_QSharedPointer::dynamicCastFailure()
     QCOMPARE(int(refCountData(baseptr)->weakref.load()), 1);
     QCOMPARE(int(refCountData(baseptr)->strongref.load()), 1);
 }
+
+void tst_QSharedPointer::dynamicCastFailureNoLeak()
+{
+    NonTracked::dynamicCastFailureNoLeak();
+}
 #endif
 
 void tst_QSharedPointer::constCorrectness()