Work around macOS's inconsistency in naming of India's time-zone

macOS fails to create a zone for the name its own systemTimeZone
claims to have (see new comment). So make sure we do consistently
recognize the name systemTimeZoneId() returns, using systemTimeZone
from which we got its name.

Add minimal testing of system time-zone.

Fixes: QTBUG-80173
Change-Id: I42f21efbd7c439158fee954d555414bb180e7f8f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/corelib/time/qtimezoneprivate_mac.mm b/src/corelib/time/qtimezoneprivate_mac.mm
index d3c4fbe5da..4509e316f9 100644
--- a/src/corelib/time/qtimezoneprivate_mac.mm
+++ b/src/corelib/time/qtimezoneprivate_mac.mm
@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Copyright (C) 2013 John Layt <jlayt@kde.org>
 ** Contact: https://www.qt.io/licensing/
 **
@@ -94,6 +95,16 @@ void QMacTimeZonePrivate::init(const QByteArray &ianaId)
         if (m_nstz)
             m_id = ianaId;
     }
+    if (!m_nstz) {
+        // 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
+        // systemTimeZoneId() returns, and use systemTimeZone if we get it:
+        m_nstz = [NSTimeZone.systemTimeZone retain];
+        Q_ASSERT(m_nstz);
+        if (QString::fromNSString(m_nstz.name).toUtf8() == ianaId)
+            m_id = ianaId;
+    }
 }
 
 QString QMacTimeZonePrivate::comment() const