1 files changed, 17 insertions, 12 deletions
diff --git a/src/corelib/time/qtimezoneprivate_mac.mm b/src/corelib/time/qtimezoneprivate_mac.mm
index b051b08ec7..da7e24d614 100644
--- a/src/corelib/time/qtimezoneprivate_mac.mm
+++ b/src/corelib/time/qtimezoneprivate_mac.mm
@@ -19,7 +19,8 @@ QT_BEGIN_NAMESPACE
 /*
     Private
 
-    OS X system implementation
+    Darwin system implementation
+    https://developer.apple.com/documentation/foundation/nstimezone
 */
 
 // Create the system default time zone
@@ -56,12 +57,10 @@ QMacTimeZonePrivate *QMacTimeZonePrivate::clone() const
 
 void QMacTimeZonePrivate::init(const QByteArray &ianaId)
 {
-    if (availableTimeZoneIds().contains(ianaId)) {
-        m_nstz = [[NSTimeZone timeZoneWithName:QString::fromUtf8(ianaId).toNSString()] retain];
-        if (m_nstz)
-            m_id = ianaId;
-    }
-    if (!m_nstz) {
+    m_nstz = [[NSTimeZone timeZoneWithName:QString::fromUtf8(ianaId).toNSString()] retain];
+    if (m_nstz) {
+        m_id = ianaId;
+    } else {
         // macOS has been seen returning a systemTimeZone which reports its name
         // as Asia/Kolkata, which doesn't appear in knownTimeZoneNames (which
         // calls the zone Asia/Calcutta). So explicitly check for the name
@@ -113,7 +112,7 @@ QString QMacTimeZonePrivate::displayName(QTimeZone::TimeType timeType,
             style = NSTimeZoneNameStyleStandard;
         break;
     case QTimeZone::OffsetName :
-        // Unreachable
+        Q_UNREACHABLE();
         break;
     }
 
@@ -149,7 +148,7 @@ int QMacTimeZonePrivate::daylightTimeOffset(qint64 atMSecsSinceEpoch) const
 
 bool QMacTimeZonePrivate::hasDaylightTime() const
 {
-    // TODO No Mac API, assume if has transitions
+    // TODO Scan transitions for one after which isDaylightSavingTimeForDate is true.
     return hasTransitions();
 }
 
@@ -191,7 +190,7 @@ QTimeZonePrivate::Data QMacTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
     const NSTimeInterval nextSecs = nextDate.timeIntervalSince1970;
     if (nextDate == nil || nextSecs <= seconds) {
         [nextDate release];
-        return invalidData();
+        return {};
     }
     tran.atMSecsSinceEpoch = nextSecs * 1000;
     tran.offsetFromUtc = [m_nstz secondsFromGMTForDate:nextDate];
@@ -204,7 +203,7 @@ QTimeZonePrivate::Data QMacTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
 QTimeZonePrivate::Data QMacTimeZonePrivate::previousTransition(qint64 beforeMSecsSinceEpoch) const
 {
     // The native API only lets us search forward, so we need to find an early-enough start:
-    const NSTimeInterval lowerBound = std::numeric_limits<NSTimeInterval>::lowest();
+    constexpr NSTimeInterval lowerBound = std::numeric_limits<NSTimeInterval>::lowest();
     const qint64 endSecs = beforeMSecsSinceEpoch / 1000;
     const int year = 366 * 24 * 3600; // a (long) year, in seconds
     NSTimeInterval prevSecs = endSecs; // sentinel for later check
@@ -274,7 +273,7 @@ QTimeZonePrivate::Data QMacTimeZonePrivate::previousTransition(qint64 beforeMSec
         return data(qint64(prevSecs * 1e3));
 
     // No transition data; or first transition later than requested time.
-    return invalidData();
+    return {};
 }
 
 QByteArray QMacTimeZonePrivate::systemTimeZoneId() const
@@ -285,6 +284,12 @@ QByteArray QMacTimeZonePrivate::systemTimeZoneId() const
     return QString::fromNSString(NSTimeZone.systemTimeZone.name).toUtf8();
 }
 
+bool QMacTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray& ianaId) const
+{
+    QMacAutoReleasePool pool;
+    return [NSTimeZone timeZoneWithName:QString::fromUtf8(ianaId).toNSString()] != nil;
+}
+
 QList<QByteArray> QMacTimeZonePrivate::availableTimeZoneIds() const
 {
     NSEnumerator *enumerator = NSTimeZone.knownTimeZoneNames.objectEnumerator;