QDateTime - Add api for Time Zone Abbreviation

Add a new method to return the time zone abbreviation for the current
time spec.  For LocalTime this is the abbreviation returned by mktime.

This new method will later be used in changes to the date formatter
and QTimeZone.

Note this change does not implement WinCE support.

[ChangeLog][QtCore][QDateTime] Add method timeZoneAbbreviation() to
return effective time zone abbreviation.

Change-Id: I265a5e96c72eb7236974f80f053f1fb341e3c816
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>

2 files changed, 107 insertions, 0 deletions

diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index 008e72af1c..db0f7d3a74 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -174,6 +174,7 @@ static void rfcDateImpl(const QString &s, QDate *dd = 0, QTime *dt = 0, int *utf
 #endif
 static QDateTimePrivate::Spec utcToLocal(QDate &date, QTime &time);
 static void utcToOffset(QDate *date, QTime *time, qint32 offset);
+static QDate adjustDate(QDate date);
 
 // Return offset in [+-]HH:MM format
 // Qt::ISODate puts : between the hours and minutes, but Qt:TextDate does not
@@ -225,6 +226,68 @@ static int fromOffsetString(const QString &offsetString, bool *valid)
     return ((hour * 60) + minute) * 60;
 }
 
+#if !defined(Q_OS_WINCE)
+// Calls the platform variant of mktime for the given date and time,
+// and updates the date, time, spec and abbreviation with the returned values
+// If the date falls outside the 1970 to 2037 range supported by mktime / time_t
+// then null date/time will be returned, you should call adjustDate() first if
+// you need a guaranteed result.
+static time_t qt_mktime(QDate *date, QTime *time, QDateTimePrivate::Spec *spec,
+                        QString *abbreviation, bool *ok)
+{
+    if (ok)
+        *ok = false;
+    int yy, mm, dd;
+    date->getDate(&yy, &mm, &dd);
+    tm local;
+    local.tm_sec = time->second();
+    local.tm_min = time->minute();
+    local.tm_hour = time->hour();
+    local.tm_mday = dd;
+    local.tm_mon = mm - 1;
+    local.tm_year = yy - 1900;
+    local.tm_wday = 0;
+    local.tm_yday = 0;
+    local.tm_isdst = -1;
+#if defined(Q_OS_WIN)
+    _tzset();
+#else
+    tzset();
+#endif // Q_OS_WIN
+    const time_t secsSinceEpoch = mktime(&local);
+    if (secsSinceEpoch != (uint)-1) {
+        *date = QDate(local.tm_year + 1900, local.tm_mon + 1, local.tm_mday);
+        *time = QTime(local.tm_hour, local.tm_min, local.tm_sec, time->msec());
+        if (local.tm_isdst == 1) {
+            if (spec)
+                *spec = QDateTimePrivate::LocalDST;
+            if (abbreviation)
+                *abbreviation = QString::fromLocal8Bit(tzname[1]);
+        } else if (local.tm_isdst == 0) {
+            if (spec)
+                *spec = QDateTimePrivate::LocalStandard;
+            if (abbreviation)
+                *abbreviation = QString::fromLocal8Bit(tzname[0]);
+        } else {
+            if (spec)
+                *spec = QDateTimePrivate::LocalUnknown;
+            if (abbreviation)
+                *abbreviation = QString::fromLocal8Bit(tzname[0]);
+        }
+        if (ok)
+            *ok = true;
+    } else {
+        *date = QDate();
+        *time = QTime();
+        if (spec)
+            *spec = QDateTimePrivate::LocalUnknown;
+        if (abbreviation)
+            *abbreviation = QString();
+    }
+    return secsSinceEpoch;
+}
+#endif // !Q_OS_WINCE
+
 /*****************************************************************************
   QDate member functions
  *****************************************************************************/
@@ -2457,6 +2520,49 @@ int QDateTime::offsetFromUtc() const
 }
 
 /*!
+    \since 5.2
+
+    Returns the Time Zone Abbreviation for the datetime.
+
+    If the timeSpec() is Qt::UTC this will be "UTC".
+
+    If the timeSpec() is Qt::OffsetFromUTC this will be in the format
+    "UTC[+-]00:00".
+
+    If the timeSpec() is Qt::LocalTime then the host system is queried for the
+    correct abbreviation.
+
+    Note that abbreviations may or may not be localized.
+
+    Note too that the abbreviation is not guaranteed to be a unique value,
+    i.e. different time zones may have the same abbreviation.
+
+    \sa timeSpec()
+*/
+
+QString QDateTime::timeZoneAbbreviation() const
+{
+    switch (d->spec) {
+    case QDateTimePrivate::UTC:
+        return QStringLiteral("UTC");
+    case QDateTimePrivate::OffsetFromUTC:
+        return QLatin1String("UTC") + toOffsetString(Qt::ISODate, d->m_offsetFromUtc);
+    default:  { // Any Qt::LocalTime
+#if defined(Q_OS_WINCE)
+        // TODO Stub to enable compilation on WinCE
+        return QString();
+#else
+        QDate dt = adjustDate(d->date);
+        QTime tm = d->time;
+        QString abbrev;
+        qt_mktime(&dt, &tm, 0, &abbrev, 0);
+        return abbrev;
+#endif // !Q_OS_WINCE
+        }
+    }
+}
+
+/*!
     Sets the date part of this datetime to \a date.
     If no time is set, it is set to midnight.
 
diff --git a/src/corelib/tools/qdatetime.h b/src/corelib/tools/qdatetime.h
index 3c8b1a9920..25f5b74eb2 100644
--- a/src/corelib/tools/qdatetime.h
+++ b/src/corelib/tools/qdatetime.h
@@ -219,6 +219,7 @@ public:
     QTime time() const;
     Qt::TimeSpec timeSpec() const;
     int offsetFromUtc() const;
+    QString timeZoneAbbreviation() const;
 
     qint64 toMSecsSinceEpoch() const;
     // ### Qt 6: use quint64 instead of uint