QDateTime - Add api for isDaylightTime()

Add new method to return if the current time is Daylight Time.

[ChangeLog][QtCore][QDateTime] Added new method isDaylightTime() to
return if the datetime is in Daylight Time or not.

Change-Id: Icb93fd5dd0b2f7d83d2d4643eeb12922c1137e3e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qdatetime.cpp

@@ -2992,6 +2992,32 @@ QString QDateTime::timeZoneAbbreviation() const
     return QString();
 }
 
+/*!
+    \since 5.2
+
+    Returns if this datetime falls in Daylight Savings Time.
+
+    If the Qt::TimeSpec is not Qt::LocalTime then will always
+    return false.
+
+    \sa timeSpec()
+*/
+
+bool QDateTime::isDaylightTime() const
+{
+    switch (d->m_spec) {
+    case Qt::UTC:
+    case Qt::OffsetFromUTC:
+        return false;
+    case Qt::LocalTime: {
+        QDateTimePrivate::DaylightStatus status;
+        localMSecsToEpochMSecs(d->m_msecs, 0, 0, &status, 0);
+        return (status == QDateTimePrivate::DaylightTime);
+        }
+    }
+    return false;
+}
+
 /*!
     Sets the date part of this datetime to \a date.
     If no time is set, it is set to midnight.

src/corelib/tools/qdatetime.h

@@ -223,6 +223,7 @@ public:
     Qt::TimeSpec timeSpec() const;
     int offsetFromUtc() const;
     QString timeZoneAbbreviation() const;
+    bool isDaylightTime() const;
 
     qint64 toMSecsSinceEpoch() const;
     // ### Qt 6: use quint64 instead of uint

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

@@ -143,6 +143,7 @@ private slots:
     void roundtripGermanLocale() const;
     void utcOffsetLessThan() const;
 
+    void isDaylightTime() const;
     void daylightTransitions() const;
 
 private:
@@ -2316,6 +2317,28 @@ void tst_QDateTime::utcOffsetLessThan() const
     QVERIFY(!(dt2 < dt1));
 }
 
+void tst_QDateTime::isDaylightTime() const
+{
+    QDateTime utc1(QDate(2012, 1, 1), QTime(0, 0, 0), Qt::UTC);
+    QVERIFY(!utc1.isDaylightTime());
+    QDateTime utc2(QDate(2012, 6, 1), QTime(0, 0, 0), Qt::UTC);
+    QVERIFY(!utc2.isDaylightTime());
+
+    QDateTime offset1(QDate(2012, 1, 1), QTime(0, 0, 0), Qt::OffsetFromUTC, 1 * 60 * 60);
+    QVERIFY(!offset1.isDaylightTime());
+    QDateTime offset2(QDate(2012, 6, 1), QTime(0, 0, 0), Qt::OffsetFromUTC, 1 * 60 * 60);
+    QVERIFY(!offset2.isDaylightTime());
+
+    if (europeanTimeZone) {
+        QDateTime cet1(QDate(2012, 1, 1), QTime(0, 0, 0));
+        QVERIFY(!cet1.isDaylightTime());
+        QDateTime cet2(QDate(2012, 6, 1), QTime(0, 0, 0));
+        QVERIFY(cet2.isDaylightTime());
+    } else {
+        QSKIP("You must test using Central European (CET/CEST) time zone, e.g. TZ=Europe/Oslo");
+    }
+}
+
 void tst_QDateTime::daylightTransitions() const
 {
     if (europeanTimeZone) {