Introduce QScopeGuard

A RAII style class which calls a function at end of scope.

Example usage:
    auto cleanup = qScopeGuard([] { <my cleanup code> ; });

[ChangeLog][QtCore] Introduced QScopeGuard.

Task-number: QTBUG-62894
Change-Id: Ife67f5c76255a1fafbae03367263da0bac9a0070
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

4 files changed, 219 insertions, 0 deletions

diff --git a/src/corelib/doc/snippets/code/src_corelib_tools_qscopeguard.cpp b/src/corelib/doc/snippets/code/src_corelib_tools_qscopeguard.cpp
new file mode 100644
index 0000000000..c8c5f694c6
--- /dev/null
+++ b/src/corelib/doc/snippets/code/src_corelib_tools_qscopeguard.cpp
@@ -0,0 +1,67 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Sérgio Martins <sergio.martins@kdab.com>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+//! [0]
+void myComplexCodeWithMultipleReturnPoints(int v)
+{
+    // The lambda will be executed right before your function returns
+    auto cleanup = qScopeGuard([] { code you want executed goes HERE; });
+
+    if (v == -1)
+        return;
+
+    int v2 = code_that_might_through_exceptions();
+
+    if (v2 == -1)
+        return;
+
+    (...)
+}
+//! [0]
diff --git a/src/corelib/tools/qscopeguard.h b/src/corelib/tools/qscopeguard.h
new file mode 100644
index 0000000000..31100fcabb
--- /dev/null
+++ b/src/corelib/tools/qscopeguard.h
@@ -0,0 +1,96 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Sérgio Martins <sergio.martins@kdab.com>
+** 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 QSCOPEGUARD_H
+#define QSCOPEGUARD_H
+
+#include <QtCore/qglobal.h>
+
+
+QT_BEGIN_NAMESPACE
+
+
+template <typename F> class QScopeGuard;
+template <typename F> QScopeGuard<F> qScopeGuard(F f);
+
+template <typename F>
+class QScopeGuard
+{
+public:
+    QScopeGuard(QScopeGuard &&other) Q_DECL_NOEXCEPT
+        : m_func(std::move(other.m_func))
+        , m_invoke(other.m_invoke)
+    {
+        other.dismiss();
+    }
+
+    ~QScopeGuard()
+    {
+        if (m_invoke)
+            m_func();
+    }
+
+    void dismiss() Q_DECL_NOEXCEPT
+    {
+        m_invoke = false;
+    }
+
+private:
+    explicit QScopeGuard(F f) Q_DECL_NOEXCEPT
+        : m_func(std::move(f))
+    {
+    }
+
+    Q_DISABLE_COPY(QScopeGuard)
+
+    F m_func;
+    bool m_invoke = true;
+    friend QScopeGuard qScopeGuard<F>(F);
+};
+
+
+template <typename F>
+QScopeGuard<F> qScopeGuard(F f)
+{
+    return QScopeGuard<F>(std::move(f));
+}
+
+QT_END_NAMESPACE
+
+#endif // QSCOPEGUARD_H
diff --git a/src/corelib/tools/qscopeguard.qdoc b/src/corelib/tools/qscopeguard.qdoc
new file mode 100644
index 0000000000..7cbc3e9c7b
--- /dev/null
+++ b/src/corelib/tools/qscopeguard.qdoc
@@ -0,0 +1,55 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Sérgio Martins <sergio.martins@kdab.com>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** 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 Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file. Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qscopeguard.h"
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \fn const QScopeGuard<F> qScopeGuard(F f)
+    \inmodule QtCore
+    \brief The qScopeGuard function can be used to call a function at the end of the scope.
+    \since 5.12
+    \ingroup misc
+
+    QScopeGuard<F> is a class which sole purpose is to run a function F in its destructor.
+    This is useful for guaranteeing your cleanup code is executed whether the function is exited normally,
+    exited early by a return statement, or exited by an exception.
+
+    If F is a lambda then you cannot instantiate the template directly, therefore the qScopeGuard() helper
+    is provided and QScopeGuard<F> is made a private implementation detail.
+
+    Example usage is as follows:
+
+    \snippet code/src_corelib_tools_qscopeguard.cpp 0
+
+    \note Exceptions are not supported. The callable shouldn't throw when executed, copied or moved.
+
+    \sa QScopedValueRollback
+*/
+
+QT_END_NAMESPACE
diff --git a/src/corelib/tools/tools.pri b/src/corelib/tools/tools.pri
index 30f7edb5f2..961a0a39ac 100644
--- a/src/corelib/tools/tools.pri
+++ b/src/corelib/tools/tools.pri
@@ -45,6 +45,7 @@ HEADERS +=  \
         tools/qregexp.h \
         tools/qringbuffer_p.h \
         tools/qrefcount.h \
+        tools/qscopeguard.h \
         tools/qscopedpointer.h \
         tools/qscopedpointer_p.h \
         tools/qscopedvaluerollback.h \