From 18439a449fdf7e60878329a42fdc55beca14b4c0 Mon Sep 17 00:00:00 2001
From: Edward Welbourne <edward.welbourne@qt.io>
Date: Fri, 15 Jul 2022 15:50:33 +0200
Subject: [PATCH] Support serializing time-zone fields in date-times more
 flexibly

[ChangeLog][QtCore][QDateTime] The 't' format character in a
toString() template can now be repeated to get alternatives to the
(unparseable) zone abbreviation. Thus 'tt' now gets the zone offset
without colon, [+-]hhmm; 'ttt' gets the same with colon, [+-]hh:mm,
and 'tttt' gets the zone name. Previously, each 't' was replaced by
another copy of the abbreviation.

Task-number: QTBUG-95966
Change-Id: Iccccd11f06fa732ed27c0e5d4e40a3d4b5f79f8d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/text/qlocale.cpp                  | 36 ++++++++++++++++---
 src/corelib/time/qdatetime.cpp                | 19 +++++++++-
 .../corelib/time/qdatetime/tst_qdatetime.cpp  |  5 +--
 3 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/src/corelib/text/qlocale.cpp b/src/corelib/text/qlocale.cpp
index e8ef690186..ba97d8cbb4 100644
--- a/src/corelib/text/qlocale.cpp
+++ b/src/corelib/text/qlocale.cpp
@@ -31,6 +31,9 @@ QT_WARNING_DISABLE_GCC("-Wfree-nonheap-object") // false positive tracking
 #include "qvariant.h"
 #include "qvarlengtharray.h"
 #include "qstringbuilder.h"
+#if QT_CONFIG(timezone)
+#   include "qtimezone.h"
+#endif
 #include "private/qnumeric_p.h"
 #include "private/qtools_p.h"
 #include <cmath>
@@ -3520,13 +3523,36 @@ QString QCalendarBackend::dateTimeToString(QStringView format, const QDateTime &
                 }
                 break;
 
-            case 't':
+            case 't': {
                 used = true;
-                repeat = 1;
-                // If we have a QDateTime use the time spec otherwise use the current system tzname
-                result.append(formatDate ? datetime.timeZoneAbbreviation()
-                                         : QDateTime::currentDateTime().timeZoneAbbreviation());
+                repeat = qMin(repeat, 4);
+                // If we don't have a date-time, use the current system time:
+                const QDateTime when = formatDate ? datetime : QDateTime::currentDateTime();
+                QString text;
+                switch (repeat) {
+#if QT_CONFIG(timezone)
+                case 4:
+                    text = when.timeZone().displayName(when, QTimeZone::LongName);
+                    break;
+#endif // timezone
+                case 3:
+                case 2:
+                    text = when.toOffsetFromUtc(when.offsetFromUtc()).timeZoneAbbreviation();
+                    // If the offset is UTC that'll be a Qt::UTC, otherwise Qt::OffsetFromUTC.
+                    Q_ASSERT(text.startsWith("UTC"_L1));
+                    // The Qt::UTC case omits the zero offset, which we want:
+                    text = text.size() == 3 ? u"+00:00"_s : text.sliced(3);
+                    if (repeat == 2) // +hhmm format, rather than +hh:mm format
+                        text = text.remove(u':');
+                    break;
+                default:
+                    text = when.timeZoneAbbreviation();
+                    break;
+                }
+                if (!text.isEmpty())
+                    result.append(text);
                 break;
+            }
 
             default:
                 break;
diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index eca8f7c18a..689bc88c24 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -1952,7 +1952,24 @@ QString QTime::toString(Qt::DateFormat format) const
              \l{QLocale::toString()}), the locale-appropriate text (returned by
              \l{QLocale::amText()} or \l{QLocale::pmText()}) is used without
              change of case.
-    \row \li t \li The timezone (for example "CEST")
+    \row \li t
+         \li The timezone abbreviation (for example "CEST"). Note that time zone
+             abbreviations are not unique. In particular, \l toString() cannot
+             parse this.
+    \row \li tt
+         \li The timezone's offset from UTC with no colon between the hours and
+             minutes (for example "+0200").
+    \row \li ttt
+         \li The timezone's offset from UTC with a colon between the hours and
+             minutes (for example "+02:00").
+    \row \li tttt
+         \li The timezone name (for example "Europe/Berlin"). Note that this
+             gives no indication of whether the date-time was in daylight-saving
+             time or standard time, which may lead to ambiguity if the date-time
+             falls in an hour repeated by a transition between the two. The name
+             used is the one provided by \l QTimeZone::displayName() with the \l
+             QTimeZone::LongName type. This may depend on the operating system
+             in use.
     \endtable
 
     Any non-empty sequence of characters enclosed in single quotes will be
diff --git a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
index d00ddb254d..4f3fc881b4 100644
--- a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
@@ -1104,8 +1104,9 @@ void tst_QDateTime::toString_strformat()
     QCOMPARE(testTime.toString("hh:mm:ss"), QString("01:02:03"));
     QCOMPARE(testTime.toString("hh:mm:ss.zz"), QString("01:02:03.456"));
     QCOMPARE(testDateTime.toString("yyyy-MM-dd hh:mm:ss t"), QString("2013-01-01 01:02:03 UTC"));
-    // TODO QTBUG-95966: find better ways to use repeated 't'
-    QCOMPARE(testDateTime.toString("yyyy-MM-dd hh:mm:ss tt"), QString("2013-01-01 01:02:03 UTCUTC"));
+    QCOMPARE(testDateTime.toString("yyyy-MM-dd hh:mm:ss tt"), QString("2013-01-01 01:02:03 +0000"));
+    QCOMPARE(testDateTime.toString("yyyy-MM-dd hh:mm:ss ttt"), QString("2013-01-01 01:02:03 +00:00"));
+    QCOMPARE(testDateTime.toString("yyyy-MM-dd hh:mm:ss tttt"), QString("2013-01-01 01:02:03 UTC"));
 }
 #endif // datestring