Fix an assertion failure in massageAdjustedDateTime()v6.2.3

The QDateTimeData &d it's passed is a copy that's about to be
modified; before we do so, we haven't detached so its internals have a
ref-count of two, contradicting an assertion in the non-const
Data::operator->(); so just directly access d.d->m_timezone, since we
know that spec == TimeZone implies !isShort().
Added test that triggered the assertion and now doesn't.

Fixes: QTBUG-99668
Change-Id: I07321ad91be5adce524be18e4ab82eee7110dc6a
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 5d228beb520d92c985497fb43fa91d2920db6cb0)

1 files changed, 12 insertions, 0 deletions

diff --git a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
index d528361bb9..4f2706bd83 100644
--- a/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
+++ b/tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp
@@ -1131,6 +1131,18 @@ void tst_QDateTime::addDays()
     QCOMPARE(dt2.timeSpec(), Qt::OffsetFromUTC);
     QCOMPARE(dt2.offsetFromUtc(), 60 * 60);
 
+#if QT_CONFIG(timezone)
+    const QTimeZone cet("Europe/Oslo");
+    if (cet.isValid()) {
+        dt1 = QDate(2022, 1, 10).startOfDay(cet);
+        dt2 = dt1.addDays(2); // QTBUG-99668: should not assert
+        QCOMPARE(dt2.date(), QDate(2022, 1, 12));
+        QCOMPARE(dt2.time(), QTime(0, 0));
+        QCOMPARE(dt2.timeSpec(), Qt::TimeZone);
+        QCOMPARE(dt2.timeZone(), cet);
+    }
+#endif
+
     // test last second of 1969 *is* valid (despite being time_t(-1))
     dt1 = QDateTime(QDate(1970, 1, 1), QTime(23, 59, 59));
     dt2 = dt1.addDays(-1);