Use localized time-zone abbreviations or offset

The actual formatting of date-time strings is handled by the calendar
backend, but the code's in qlocale.cpp as it uses some of its tools.
When feature timezone is unavailable, we're stuck (as before) with
using QDateTime::timeZoneAbbreviation(), but when it's available we
can use QTimeZone::displayName() to get the localized form of the
abbreviation and offset string.

Make matching changes in QDTP so that it recognizes these localized
abbreviations. We now have another candidate for what local time might
be called, to add to those that must be checked.

This naturally implied some changes to tests. It turns out ICU
believes en_US uses GMT+1/GMT+2 for CET/CEST. Replace some MS
QEXPECT_FAIL()s by including the non-abbreviations we do in fact use
on MS in the lists of "abbreviations" to accept.

[ChangeLog][QtCore][QLocale] When a datetime format includes the
timezone (or offset), the appropriately localised form is (to the
extent the timezone backend in use supports this) used where,
previously, a haphazard choice of system and C locale was used. This
applies to both serialization and parsing.

Task-number: QTBUG-115158
Change-Id: I04f9c1055c3b9008320bb8b758490287fd8be5cd
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 35 insertions, 9 deletions

diff --git a/tests/auto/corelib/time/qdatetimeparser/tst_qdatetimeparser.cpp b/tests/auto/corelib/time/qdatetimeparser/tst_qdatetimeparser.cpp
index 7f97e551a6..1da4affefb 100644
--- a/tests/auto/corelib/time/qdatetimeparser/tst_qdatetimeparser.cpp
+++ b/tests/auto/corelib/time/qdatetimeparser/tst_qdatetimeparser.cpp
@@ -4,6 +4,8 @@
 #include <QTest>
 #include <private/qdatetimeparser_p.h>
 
+using namespace Qt::StringLiterals;
+
 QT_BEGIN_NAMESPACE
 
 // access to needed members in QDateTimeParser
@@ -58,11 +60,11 @@ void tst_QDateTimeParser::reparse()
 {
     const QDateTime when = QDate(2023, 6, 15).startOfDay();
     // QTBUG-114575: 6.2 through 6.5 got back a bogus Qt::TimeZone (with zero offset):
-    const Qt::TimeSpec spec = ([](QStringView name) {
+    const auto expect = ([](QStringView name) {
         // When local time is UTC or a fixed offset from it, the parser prefers
         // to interpret a UTC or offset suffix as such, rather than as local
         // time (thereby avoiding DST-ness checks). We have to match that here.
-        if (name == QLatin1StringView("UTC"))
+        if (name == "UTC"_L1)
             return Qt::UTC;
         if (name.startsWith(u'+') || name.startsWith(u'-')) {
             if (std::all_of(name.begin() + 1, name.end(), [](QChar ch) { return ch == u'0'; }))
@@ -72,17 +74,41 @@ void tst_QDateTimeParser::reparse()
             // Potential hh:mm offset ?  Not yet seen as local tzname[] entry.
         }
         return Qt::LocalTime;
-    })(when.timeZoneAbbreviation());
+    });
 
     const QStringView format = u"dd/MM/yyyy HH:mm t";
     QDateTimeParser who(QMetaType::QDateTime, QDateTimeParser::DateTimeEdit);
     QVERIFY(who.parseFormat(format));
-    const auto state = who.parse(when.toString(format), -1, when, false);
-    QCOMPARE(state.state, QDateTimeParser::Acceptable);
-    QVERIFY(!state.conflicts);
-    QCOMPARE(state.padded, 0);
-    QCOMPARE(state.value.timeSpec(), spec);
-    QCOMPARE(state.value, when);
+    {
+        // QDTP defaults to the system locale.
+        const auto state = who.parse(QLocale::system().toString(when, format), -1, when, false);
+        QCOMPARE(state.state, QDateTimeParser::Acceptable);
+        QVERIFY(!state.conflicts);
+        QCOMPARE(state.padded, 0);
+        QCOMPARE(state.value.timeSpec(), expect(when.timeZoneAbbreviation()));
+        QCOMPARE(state.value, when);
+    }
+    {
+        // QDT::toString() uses the C locale:
+        who.setDefaultLocale(QLocale::c());
+        const QString zoneName = ([when]() {
+#if QT_CONFIG(timezone)
+            if (QLocale::c() != QLocale::system()) {
+                const QString local = when.timeRepresentation().displayName(
+                    when, QTimeZone::ShortName, QLocale::c());
+                if (!local.isEmpty())
+                    return local;
+            }
+#endif
+            return when.timeZoneAbbreviation();
+        })();
+        const auto state = who.parse(when.toString(format), -1, when, false);
+        QCOMPARE(state.state, QDateTimeParser::Acceptable);
+        QVERIFY(!state.conflicts);
+        QCOMPARE(state.padded, 0);
+        QCOMPARE(state.value.timeSpec(), expect(zoneName));
+        QCOMPARE(state.value, when);
+    }
 }
 
 void tst_QDateTimeParser::parseSection_data()