KConfig: fix using KSharedConfig in global object destructor.

ksharedconfig_in_global_object.cpp is now in kdelibs4 too
(where it works) and reproduces Albert's KgDifficulty testcase.

CHANGELOG: fix assert when using KSharedConfig in a global object destructor.
REVIEW: 122232

autotests/CMakeLists.txt

@@ -37,6 +37,7 @@ ecm_add_tests(
    kdesktopfiletest.cpp
    ksharedconfigtest.cpp
    test_kconf_update.cpp
+   ksharedconfig_in_global_object
    NAME_PREFIX kconfigcore-
    LINK_LIBRARIES KF5::ConfigCore Qt5::Test Qt5::Concurrent
 )

autotests/ksharedconfig_in_global_object.cpp

@@ -0,0 +1,62 @@
+/*  This file is part of the KDE project
+    Copyright (C) 2007 Matthias Kretz <kretz@kde.org>
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Library General Public
+    License version 2 as published by the Free Software Foundation.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Library General Public License for more details.
+
+    You should have received a copy of the GNU Library General Public License
+    along with this library; see the file COPYING.LIB.  If not, write to
+    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+    Boston, MA 02110-1301, USA.
+
+*/
+
+#include <QtCore/QCoreApplication>
+#include <QtCore/QtGlobal>
+#include <QTimer>
+#include <ksharedconfig.h>
+#include <kconfiggroup.h>
+#include <stdio.h>
+
+class Tester
+{
+public:
+    void initConfig();
+    ~Tester();
+};
+
+void Tester::initConfig()
+{
+    fprintf(stderr, "app Tester\n");
+    KConfigGroup group(KSharedConfig::openConfig(), "test");
+    group.writeEntry("test", 0);
+}
+
+Tester::~Tester()
+{
+    fprintf(stderr, "app ~Tester\n");
+    KConfigGroup group(KSharedConfig::openConfig(), "test");
+    group.writeEntry("test", 1);
+}
+
+Q_GLOBAL_STATIC(Tester, globalTestObject)
+
+int main(int argc, char **argv)
+{
+    qputenv("QT_FATAL_WARNINGS", "1");
+    QCoreApplication app(argc, argv);
+
+    KSharedConfig::Ptr config = KSharedConfig::openConfig();
+
+    Tester *t = globalTestObject();
+    t->initConfig();
+
+    QTimer::singleShot(0, qApp, SLOT(quit()));
+    return app.exec();
+}

src/core/kconfig.cpp

@@ -530,23 +530,35 @@ KConfig::OpenFlags KConfig::openFlags() const
     return d->openFlags;
 }
 
-Q_GLOBAL_STATIC(QString, globalMainConfigName)
+struct KConfigStaticData
+{
+    QString globalMainConfigName;
+    // Keep a copy so we can use it in global dtors, after qApp is gone
+    // This is a workaround for the Qt bug fixed in https://codereview.qt-project.org/107005 for Qt 5.5
+    // Revert this addition once we can depend on Qt 5.5.
+    QStringList appArgs;
+};
+Q_GLOBAL_STATIC(KConfigStaticData, globalData)
 
 void KConfig::setMainConfigName(const QString &str)
 {
-    *globalMainConfigName() = str;
+    globalData()->globalMainConfigName = str;
 }
 
 QString KConfig::mainConfigName()
 {
+    KConfigStaticData* data = globalData();
+    if (data->appArgs.isEmpty())
+        data->appArgs = QCoreApplication::arguments();
+
     // --config on the command line overrides everything else
-    const QStringList args = QCoreApplication::arguments();
+    const QStringList args = data->appArgs;
     for (int i = 1; i < args.count(); ++i) {
         if (args.at(i) == QLatin1String("--config") && i < args.count() - 1) {
             return args.at(i + 1);
         }
     }
-    const QString globalName = *globalMainConfigName();
+    const QString globalName = data->globalMainConfigName;
     if (!globalName.isEmpty()) {
         return globalName;
     }