Move locale-switching code in tests to a shared header

QLocale and QString tests had copies of a TransientLocale; we've
recently improved the QLocale one. Rather than duplicating those
rather complicated improvements, finally share a common version.

In the process, I noticed that setlocale() only returns the prior
value when passed nullptr as the new value; so rework the
implementation to get that right, so that it now correctly restores
the prior locale. That, in turn, means there's now a later call to
setlocale(), when we actually set the changed setting, which may
invalidate the earlier return; so copy it to a QByteArray before the
second call.

Included Ivan Solovev's improved version of how to reset the locale,
since TransientLocale needs it.

Pick-to: 6.2
Change-Id: I4cb1efbda42f0e2cdd934e04b3b3732ce0f45a06
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

3 files changed, 117 insertions, 66 deletions

diff --git a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
index 31f9bd9d33..d68af22585 100644
--- a/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
+++ b/tests/auto/corelib/text/qlocale/tst_qlocale.cpp
@@ -39,12 +39,12 @@
 # include <qprocess.h>
 #endif
 #include <float.h>
-#include <locale.h>
 
 #include <qlocale.h>
 #include <private/qlocale_p.h>
 #include <private/qlocale_tools_p.h>
 #include <qnumeric.h>
+#include "../../../../shared/localechange.h"
 
 #if defined(Q_OS_LINUX) && !defined(__UCLIBC__)
 #    define QT_USE_FENV
@@ -176,58 +176,7 @@ private:
     bool europeanTimeZone;
     void toReal_data();
 
-    class TransientLocale
-    {
-        const int m_category;
-        const char *const m_prior;
-#if !defined(QT_NO_SYSTEMLOCALE) && defined(Q_OS_UNIX) \
-    && (!defined(Q_OS_DARWIN) || defined(Q_OS_NACL))
-#define TRANSIENT_ENV
-        // Unix system locale consults environment variables, so we need to set
-        // the appropriate one, too.
-        const QByteArray m_envVar, m_envPrior;
-        const bool m_envSet;
-        static QByteArray categoryToEnv(int category)
-        {
-            switch (category) {
-#define CASE(cat) case cat: return #cat
-            CASE(LC_ALL); CASE(LC_NUMERIC); CASE(LC_TIME); CASE(LC_MONETARY);
-            CASE(LC_MESSAGES); CASE(LC_MEASUREMENT); CASE(LC_COLLATE);
-#undef CASE
-            // Nothing in our code pays attention to any other LC_*
-            default:
-                Q_UNREACHABLE();
-                qFatal("You need to add a case for this category");
-            }
-        }
-#endif // TRANSIENT_ENV
-    public:
-        TransientLocale(int category, const char *locale)
-            : m_category(category),
-              m_prior(setlocale(category, locale))
-#ifdef TRANSIENT_ENV
-            , m_envVar(categoryToEnv(category)),
-              m_envPrior(qgetenv(m_envVar.constData())),
-              m_envSet(qputenv(m_envVar.constData(), locale))
-#endif
-        {
-            QSystemLocale dummy; // to provoke a refresh of the system locale
-        }
-        ~TransientLocale()
-        {
-#ifdef TRANSIENT_ENV
-            if (m_envSet) {
-                if (m_envPrior.isEmpty())
-                    qunsetenv(m_envVar.constData());
-                else
-                    qputenv(m_envVar.constData(), m_envPrior);
-            }
-#endif
-            setlocale(m_category, m_prior);
-            QSystemLocale dummy; // to provoke a refresh of the system locale
-        }
-#undef TRANSIENT_ENV
-    };
+    using TransientLocale = QTestLocaleChange::TransientLocale;
 };
 
 tst_QLocale::tst_QLocale()
@@ -2242,7 +2191,7 @@ public:
         setWinLocaleInfo(LOCALE_SNATIVEDIGITS, m_digits);
         setWinLocaleInfo(LOCALE_IDIGITSUBSTITUTION, m_subst);
 
-        QSystemLocale dummy; // to provoke a refresh of the system locale
+        QTestLocaleChange::resetSystemLocale();
     }
 
     QString m_decimal, m_thousand, m_sdate, m_ldate, m_stime, m_ltime, m_digits, m_subst;
@@ -2268,8 +2217,7 @@ void tst_QLocale::windowsDefaultLocale()
     setWinLocaleInfo(LOCALE_IDIGITSUBSTITUTION, u"2");
     // NB: when adding to the system things being set, be sure to update RestoreLocaleHelper, too.
 
-    QSystemLocale dummy; // to provoke a refresh of the system locale
-    QLocale locale = QLocale::system();
+    QLocale locale = QTestLocaleChange::resetSystemLocale();
 
     // Make sure we are seeing the system's format strings
     QCOMPARE(locale.zeroDigit(), QStringView(u"\u3007"));
diff --git a/tests/auto/corelib/text/qstring/tst_qstring.cpp b/tests/auto/corelib/text/qstring/tst_qstring.cpp
index a377834025..f6e7563774 100644
--- a/tests/auto/corelib/text/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/text/qstring/tst_qstring.cpp
@@ -60,6 +60,7 @@
 #include <ctype.h>
 
 #include "../shared/test_number_shared.h"
+#include "../../../../shared/localechange.h"
 
 #define CREATE_VIEW(string)                                              \
     const QString padded = QLatin1Char(' ') + string + QLatin1Char(' '); \
@@ -329,16 +330,7 @@ class tst_QString : public QObject
     void insert_impl() const { insert_impl<ArgType, QString &(QString::*)(qsizetype, const ArgType&)>(); }
     void insert_data(bool emptyIsNoop = false);
 
-    class TransientLocale
-    {
-        const int m_category;
-        const char *const m_prior;
-    public:
-        TransientLocale(int category, const char *locale)
-            : m_category(category), m_prior(setlocale(category, locale)) {}
-        bool isValid() const { return !!m_prior; }
-        ~TransientLocale() { if (m_prior) setlocale(m_category, m_prior); }
-    };
+    using TransientLocale = QTestLocaleChange::TransientLocale;
 
     class TransientDefaultLocale
     {
diff --git a/tests/shared/localechange.h b/tests/shared/localechange.h
new file mode 100644
index 0000000000..135909eea5
--- /dev/null
+++ b/tests/shared/localechange.h
@@ -0,0 +1,111 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** 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 General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** 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-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QT_TESTS_SHARED_LOCALE_CHANGE_H
+#define QT_TESTS_SHARED_LOCALE_CHANGE_H
+#include <qglobal.h>
+#include <QtCore/QByteArray>
+#include <QtCore/QLocale>
+#include <private/qlocale_p.h>
+
+#include <locale.h>
+
+namespace QTestLocaleChange {
+
+    QLocale resetSystemLocale()
+    {
+#ifndef QT_NO_SYSTEMLOCALE
+        { // Transient instance marks system locale data as stale:
+            QSystemLocale dummy;
+        } // Now we can reinitialize:
+#endif
+        return QLocale::system();
+    }
+
+    class TransientLocale
+    {
+        const int m_category;
+        const QByteArray m_prior;
+        const bool m_didSet;
+#if !defined(QT_NO_SYSTEMLOCALE) && defined(Q_OS_UNIX) \
+    && (!defined(Q_OS_DARWIN) || defined(Q_OS_NACL))
+#define TRANSIENT_ENV
+        // Unix system locale consults environment variables, so we need to set
+        // the appropriate one, too.
+        const QByteArray m_envVar, m_envPrior;
+        const bool m_envSet;
+        static QByteArray categoryToEnv(int category)
+        {
+            switch (category) {
+#define CASE(cat) case cat: return #cat
+            CASE(LC_ALL); CASE(LC_NUMERIC); CASE(LC_TIME); CASE(LC_MONETARY);
+            CASE(LC_MESSAGES); CASE(LC_MEASUREMENT); CASE(LC_COLLATE);
+#undef CASE
+            // Nothing in our code pays attention to any other LC_*
+            default:
+                Q_UNREACHABLE();
+                qFatal("You need to add a case for this category");
+            }
+        }
+#endif // TRANSIENT_ENV
+    public:
+        TransientLocale(int category, const char *locale)
+            : m_category(category),
+              m_prior(setlocale(category, nullptr)),
+              // That return value may be stomped by this later call, so we copy
+              // it to a QByteArray for safe keeping.
+              m_didSet(setlocale(category, locale) != nullptr)
+#ifdef TRANSIENT_ENV
+            , m_envVar(categoryToEnv(category)),
+              m_envPrior(qgetenv(m_envVar.constData())),
+              m_envSet(qputenv(m_envVar.constData(), locale))
+#endif
+        {
+            resetSystemLocale();
+        }
+        ~TransientLocale()
+        {
+#ifdef TRANSIENT_ENV
+            if (m_envSet) {
+                if (m_envPrior.isEmpty())
+                    qunsetenv(m_envVar.constData());
+                else
+                    qputenv(m_envVar.constData(), m_envPrior);
+            }
+#endif
+            if (m_prior.size())
+                setlocale(m_category, m_prior.constData());
+            resetSystemLocale();
+        }
+#undef TRANSIENT_ENV
+
+        bool isValid() const { return m_didSet; }
+    };
+}
+
+#endif // QT_TESTS_SHARED_LOCALE_CHANGE_H