Fix handling of Sunday in POSIX time-zone rules

Dating from the origins of our support for the zoneinfo file format,
the mapping of POSIX's day-numbering (0 = Sunday through 6 = Saturday,
see [*]) to Qt's (1 = Monday through 7 = Sunday) was done by mapping 0
to 1, when it should have been 7.

[*] http://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html

Corrected a QTimeZone test that trusted the results it got without
checking which day of the week those were: they were all Mondays.
Verified that the corrected dates are in fact Sundays.
Checked the zone abbreviations, too.

Fixes: QTBUG-90553
Change-Id: I84b4b14f9892ff687918cd3c42c7c9807e45313c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
(cherry picked from commit 38a72af4fd311219779f89b2b78cd56d879f61db)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 20 insertions, 13 deletions

diff --git a/src/corelib/time/qtimezoneprivate_tz.cpp b/src/corelib/time/qtimezoneprivate_tz.cpp
index 938f8d119a..0b97d39091 100644
--- a/src/corelib/time/qtimezoneprivate_tz.cpp
+++ b/src/corelib/time/qtimezoneprivate_tz.cpp
@@ -372,8 +372,8 @@ static QDate calculatePosixDate(const QByteArray &dateRule, int year)
         int month = dateParts.at(0).mid(1).toInt();
         int week = dateParts.at(1).toInt();
         int dow = dateParts.at(2).toInt();
-        if (dow == 0)
-            ++dow;
+        if (dow == 0) // Sunday; we represent it as 7
+            dow = 7;
         return calculateDowDate(year, month, dow, week);
     } else if (dateRule.at(0) == 'J') {
         // Day of Year ignores Feb 29
diff --git a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
index 0103f92434..a86816d6a9 100644
--- a/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
+++ b/tests/auto/corelib/time/qtimezone/tst_qtimezone.cpp
@@ -1180,11 +1180,14 @@ void tst_QTimeZone::tzTest()
     QCOMPARE(dat.standardTimeOffset, 3600);
     QCOMPARE(dat.daylightTimeOffset, 0);
 
-    // Known high datetimes
-    qint64 stdHi = QDateTime(QDate(2100, 1, 1), QTime(0, 0, 0), Qt::UTC).toMSecsSinceEpoch();
-    qint64 dstHi = QDateTime(QDate(2100, 6, 1), QTime(0, 0, 0), Qt::UTC).toMSecsSinceEpoch();
+    // Date-times late enough to exercise POSIX rules:
+    qint64 stdHi = QDate(2100, 1, 1).startOfDay(Qt::UTC).toMSecsSinceEpoch();
+    qint64 dstHi = QDate(2100, 6, 1).startOfDay(Qt::UTC).toMSecsSinceEpoch();
+    // Relevant last Sundays in October and March:
+    QCOMPARE(Qt::DayOfWeek(QDate(2099, 10, 25).dayOfWeek()), Qt::Sunday);
+    QCOMPARE(Qt::DayOfWeek(QDate(2100, 3, 28).dayOfWeek()), Qt::Sunday);
+    QCOMPARE(Qt::DayOfWeek(QDate(2100, 10, 31).dayOfWeek()), Qt::Sunday);
 
-    // Tets high dates use the POSIX rule
     dat = tzp.data(stdHi);
     QCOMPARE(dat.atMSecsSinceEpoch - stdHi, (qint64)0);
     QCOMPARE(dat.offsetFromUtc, 3600);
@@ -1198,29 +1201,33 @@ void tst_QTimeZone::tzTest()
     QCOMPARE(dat.daylightTimeOffset, 3600);
 
     dat = tzp.previousTransition(stdHi);
-    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::OffsetFromUTC, 3600),
-             QDateTime(QDate(2099, 10, 26), QTime(2, 0), Qt::OffsetFromUTC, 3600));
+    QCOMPARE(dat.abbreviation, QStringLiteral("CET"));
+    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::UTC),
+             QDateTime(QDate(2099, 10, 25), QTime(3, 0), Qt::OffsetFromUTC, 7200));
     QCOMPARE(dat.offsetFromUtc, 3600);
     QCOMPARE(dat.standardTimeOffset, 3600);
     QCOMPARE(dat.daylightTimeOffset, 0);
 
     dat = tzp.previousTransition(dstHi);
-    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::OffsetFromUTC, 3600),
-             QDateTime(QDate(2100, 3, 29), QTime(2, 0), Qt::OffsetFromUTC, 3600));
+    QCOMPARE(dat.abbreviation, QStringLiteral("CEST"));
+    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::UTC),
+             QDateTime(QDate(2100, 3, 28), QTime(2, 0), Qt::OffsetFromUTC, 3600));
     QCOMPARE(dat.offsetFromUtc, 7200);
     QCOMPARE(dat.standardTimeOffset, 3600);
     QCOMPARE(dat.daylightTimeOffset, 3600);
 
     dat = tzp.nextTransition(stdHi);
-    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::OffsetFromUTC, 3600),
-             QDateTime(QDate(2100, 3, 29), QTime(2, 0), Qt::OffsetFromUTC, 3600));
+    QCOMPARE(dat.abbreviation, QStringLiteral("CEST"));
+    QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::UTC),
+             QDateTime(QDate(2100, 3, 28), QTime(2, 0), Qt::OffsetFromUTC, 3600));
     QCOMPARE(dat.offsetFromUtc, 7200);
     QCOMPARE(dat.standardTimeOffset, 3600);
     QCOMPARE(dat.daylightTimeOffset, 3600);
 
     dat = tzp.nextTransition(dstHi);
+    QCOMPARE(dat.abbreviation, QStringLiteral("CET"));
     QCOMPARE(QDateTime::fromMSecsSinceEpoch(dat.atMSecsSinceEpoch, Qt::OffsetFromUTC, 3600),
-             QDateTime(QDate(2100, 10, 25), QTime(2, 0), Qt::OffsetFromUTC, 3600));
+             QDateTime(QDate(2100, 10, 31), QTime(3, 0), Qt::OffsetFromUTC, 7200));
     QCOMPARE(dat.offsetFromUtc, 3600);
     QCOMPARE(dat.standardTimeOffset, 3600);
     QCOMPARE(dat.daylightTimeOffset, 0);