Fix QDateTime::toString(Qt::ISODate)'s handling of Qt::TimeZone

When the time is specified relative to a zone, the ISO date produced
lacked its offset suffix; all zones were treated as if they were local
time.  Handle zone as for an offset from UTC and ensure we do set the
date-time objects's offset from UTC when it's zone-based.

Change-Id: I7c9896bb8ec0a9d89df14a6e94b005174ab9e943
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qdatetime.cpp

@@ -2576,6 +2576,13 @@ static inline Qt::TimeSpec getSpec(const QDateTimeData &d)
     return extractSpec(getStatus(d));
 }
 
+#if QT_CONFIG(timezone)
+void QDateTimePrivate::setUtcOffsetByTZ(qint64 atMSecsSinceEpoch)
+{
+    m_offsetFromUtc = m_timeZone.d->offsetFromUtc(atMSecsSinceEpoch);
+}
+#endif
+
 // Refresh the LocalTime validity and offset
 static void refreshDateTime(QDateTimeData &d)
 {
@@ -2591,10 +2598,12 @@ static void refreshDateTime(QDateTimeData &d)
 #if QT_CONFIG(timezone)
     // If not valid time zone then is invalid
     if (spec == Qt::TimeZone) {
-        if (!d->m_timeZone.isValid())
+        if (!d->m_timeZone.isValid()) {
             status &= ~QDateTimePrivate::ValidDateTime;
-        else
+        } else {
             epochMSecs = QDateTimePrivate::zoneMSecsToEpochMSecs(msecs, d->m_timeZone, extractDaylightStatus(status), &testDate, &testTime);
+            d->setUtcOffsetByTZ(epochMSecs);
+        }
     }
 #endif // timezone
 
@@ -3822,6 +3831,9 @@ QString QDateTime::toString(Qt::DateFormat format) const
             buf += QLatin1Char('Z');
             break;
         case Qt::OffsetFromUTC:
+#if QT_CONFIG(timezone)
+        case Qt::TimeZone:
+#endif
             buf += toOffsetString(Qt::ISODate, offsetFromUtc());
             break;
         default:

src/corelib/tools/qdatetime_p.h

@@ -136,6 +136,9 @@ class QDateTimePrivate
     static qint64 zoneMSecsToEpochMSecs(qint64 msecs, const QTimeZone &zone,
                                         DaylightStatus hint = UnknownDaylightTime,
                                         QDate *localDate = 0, QTime *localTime = 0);
+
+    // Inlined for its one caller in qdatetime.cpp
+    inline void setUtcOffsetByTZ(qint64 atMSecsSinceEpoch);
 #endif // timezone
 
     static inline qint64 minJd() { return QDate::minJd(); }

tests/auto/corelib/tools/qdatetime/tst_qdatetime.cpp

@@ -77,6 +77,7 @@ private slots:
     void fromMSecsSinceEpoch();
     void toString_isoDate_data();
     void toString_isoDate();
+    void toString_isoDate_extra();
     void toString_textDate_data();
     void toString_textDate();
     void toString_rfcDate_data();
@@ -794,6 +795,28 @@ void tst_QDateTime::toString_isoDate()
     QLocale::setDefault(oldLocale);
 }
 
+void tst_QDateTime::toString_isoDate_extra()
+{
+    QDateTime dt = QDateTime::fromMSecsSinceEpoch(0, Qt::UTC);
+    QCOMPARE(dt.toString(Qt::ISODate), QLatin1String("1970-01-01T00:00:00Z"));
+#if QT_CONFIG(timezone)
+    QTimeZone PST("America/Vancouver");
+    if (PST.isValid()) {
+        dt = QDateTime::fromMSecsSinceEpoch(0, PST);
+        QCOMPARE(dt.toString(Qt::ISODate), QLatin1String("1969-12-31T16:00:00-08:00"));
+    } else {
+        qDebug("Missed zone test: no America/Vancouver zone available");
+    }
+    QTimeZone CET("Europe/Berlin");
+    if (CET.isValid()) {
+        dt = QDateTime::fromMSecsSinceEpoch(0, CET);
+        QCOMPARE(dt.toString(Qt::ISODate), QLatin1String("1970-01-01T01:00:00+01:00"));
+    } else {
+        qDebug("Missed zone test: no Europe/Berlin zone available");
+    }
+#endif // timezone
+}
+
 void tst_QDateTime::toString_textDate_data()
 {
     QTest::addColumn<QDateTime>("datetime");