Add _tzset() call before mktime() on MS

Add a change-of-zone manual test, based on a bug-report by Felix
Kälberer. This failed: debugging revealed that MS's mktime() doesn't
pick up a change to system zone.

Fixes: QTBUG-83881
Change-Id: I9b86398ef870627a059e269f85a0f5d9d9de284b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/global/qtenvironmentvariables.cpp

@@ -353,6 +353,10 @@ void qTzSet()
 time_t qMkTime(struct tm *when)
 {
     const auto locker = qt_scoped_lock(environmentMutex);
+#if defined(Q_OS_WIN)
+    // QTBUG-83881 MS's mktime() seems to need _tzset() called first.
+    _tzset();
+#endif
     return mktime(when);
 }
 

tests/manual/CMakeLists.txt

@@ -6,6 +6,7 @@ if(UIKIT)
     return()
 endif()
 
+add_subdirectory(corelib)
 add_subdirectory(filetest)
 # diaglib is broken in dev due to missing
 # QtOpenGL/QGLFunctions headers

tests/manual/corelib/CMakeLists.txt

@@ -0,0 +1,6 @@
+# Copyright (C) 2023 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+add_subdirectory(time)
+# Needs conversion from qmake:
+# add_subdirectory(tools)

tests/manual/corelib/time/CMakeLists.txt

@@ -0,0 +1,4 @@
+# Copyright (C) 2023 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+add_subdirectory(zonechange)

tests/manual/corelib/time/zonechange/CMakeLists.txt

@@ -0,0 +1,9 @@
+# Copyright (C) 2023 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+qt_internal_add_manual_test(zonechange
+    SOURCES
+        tst_zonechange.cpp
+    LIBRARIES
+        Qt::Core
+)

tests/manual/corelib/time/zonechange/tst_zonechange.cpp

@@ -0,0 +1,60 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#include <QtCore/qcoreapplication.h>
+
+#include <QtCore/qdatetime.h>
+#if QT_CONFIG(timezone)
+#include <QtCore/qtimezone.h>
+#endif
+
+#include <chrono>
+#include <thread>
+
+using namespace std::chrono;
+
+bool distinct(const QDateTime &left, const QDateTime &right)
+{
+    if (left == right)
+        return false;
+
+    qInfo() << "  Actual:" << left << "\nExpected:" << right;
+    return true;
+}
+
+// Exit status: 0 success, 1 test failed, 2 test not viable.
+int main(int argc, char **argv)
+{
+    // Other things may need this indirectly, so make sure it exists:
+    QCoreApplication ignored(argc, argv);
+    if (!qEnvironmentVariableIsEmpty("TZ")) {
+        qInfo("Environment variable TZ over-rides system setting; you need to clear it.");
+        return 2;
+    }
+
+    QDateTime date = QDateTime(QDate(2020, 2, 20), QTime(20, 20, 20));
+    QDateTime copy = date;
+    if (distinct(date, copy))
+        return 1;
+#if QT_CONFIG(timezone)
+    const auto prior = QTimeZone::systemTimeZoneId();
+#endif
+
+    qInfo("You have two minutes in which to change the system time-zone setting.");
+    std::this_thread::sleep_for(120s);
+#if QT_CONFIG(timezone)
+    if (QTimeZone::systemTimeZoneId() == prior) {
+        qInfo("Too slow.");
+        return 2;
+    }
+#endif
+
+    if (distinct(copy, date))
+        return 1;
+    QDateTime copy2 = copy.addMSecs(2);
+    QDateTime date2 = date.addMSecs(2);
+    if (distinct(copy2, date2))
+        return 1;
+
+    return 0;
+}