Fix crash when a date-time has an invalid time-zone

QDateTime is a friend of QTimeZone, so can access its internals; but
it must check the zone is valid before doing so.

Expanded tst_QDateTime::invalid() and made it data-driven to catch the
failure cases.

Commented on a test-case that caught a mistake in my first attempt at
this, and on QDateTimeParser's surprising reliance on a quirk of
QDateTime::toMSecsSinceEpoch()'s behavior.

Fixes: QTBUG-80146
Change-Id: I24856e19ff9bf402152d17d71f83be84e366faad
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

2 files changed, 23 insertions, 11 deletions

diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index 9b0bc688c9..8de4f7caf8 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -3410,6 +3410,7 @@ inline qint64 QDateTimePrivate::zoneMSecsToEpochMSecs(qint64 zoneMSecs, const QT
                                                       DaylightStatus hint,
                                                       QDate *zoneDate, QTime *zoneTime)
 {
+    Q_ASSERT(zone.isValid());
     // Get the effective data from QTimeZone
     QTimeZonePrivate::Data data = zone.d->dataForLocalTime(zoneMSecs, int(hint));
     // Docs state any time before 1970-01-01 will *not* have any DST applied
@@ -3799,8 +3800,9 @@ QTimeZone QDateTime::timeZone() const
     case Qt::OffsetFromUTC:
         return QTimeZone(d->m_offsetFromUtc);
     case Qt::TimeZone:
-        Q_ASSERT(d->m_timeZone.isValid());
-        return d->m_timeZone;
+        if (d->m_timeZone.isValid())
+            return d->m_timeZone;
+        break;
     case Qt::LocalTime:
         return QTimeZone::systemTimeZone();
     }
@@ -3884,6 +3886,7 @@ QString QDateTime::timeZoneAbbreviation() const
 #if !QT_CONFIG(timezone)
         break;
 #else
+        Q_ASSERT(d->m_timeZone.isValid());
         return d->m_timeZone.d->abbreviation(toMSecsSinceEpoch());
 #endif // timezone
     case Qt::LocalTime:  {
@@ -3920,6 +3923,7 @@ bool QDateTime::isDaylightTime() const
 #if !QT_CONFIG(timezone)
         break;
 #else
+        Q_ASSERT(d->m_timeZone.isValid());
         return d->m_timeZone.d->isDaylightTime(toMSecsSinceEpoch());
 #endif // timezone
     case Qt::LocalTime: {
@@ -4044,6 +4048,10 @@ void QDateTime::setTimeZone(const QTimeZone &toZone)
 */
 qint64 QDateTime::toMSecsSinceEpoch() const
 {
+    // Note: QDateTimeParser relies on this producing a useful result, even when
+    // !isValid(), at least when the invalidity is a time in a fall-back (that
+    // we'll have adjusted to lie outside it, but marked invalid because it's
+    // not what was asked for). Other things may be doing similar.
     switch (getSpec(d)) {
     case Qt::UTC:
         return getMSecs(d);
@@ -4058,12 +4066,13 @@ qint64 QDateTime::toMSecsSinceEpoch() const
     }
 
     case Qt::TimeZone:
-#if !QT_CONFIG(timezone)
-        return 0;
-#else
-        return QDateTimePrivate::zoneMSecsToEpochMSecs(d->m_msecs, d->m_timeZone,
-                                                       extractDaylightStatus(getStatus(d)));
+#if QT_CONFIG(timezone)
+        if (d->m_timeZone.isValid()) {
+            return QDateTimePrivate::zoneMSecsToEpochMSecs(d->m_msecs, d->m_timeZone,
+                                                           extractDaylightStatus(getStatus(d)));
+        }
 #endif
+        return 0;
     }
     Q_UNREACHABLE();
     return 0;
@@ -4158,9 +4167,11 @@ void QDateTime::setMSecsSinceEpoch(qint64 msecs)
     case Qt::TimeZone:
         Q_ASSERT(!d.isShort());
 #if QT_CONFIG(timezone)
+        d.detach();
+        if (!d->m_timeZone.isValid())
+            break;
         // Docs state any LocalTime before 1970-01-01 will *not* have any DST applied
         // but all affected times afterwards will have DST applied.
-        d.detach();
         if (msecs >= 0) {
             status = mergeDaylightStatus(status,
                                          d->m_timeZone.d->isDaylightTime(msecs)
@@ -4433,7 +4444,7 @@ static inline void massageAdjustedDateTime(const QDateTimeData &d, QDate *date,
         QDateTimePrivate::DaylightStatus status = QDateTimePrivate::UnknownDaylightTime;
         localMSecsToEpochMSecs(timeToMSecs(*date, *time), &status, date, time);
 #if QT_CONFIG(timezone)
-    } else if (spec == Qt::TimeZone) {
+    } else if (spec == Qt::TimeZone && d->m_timeZone.isValid()) {
         QDateTimePrivate::zoneMSecsToEpochMSecs(timeToMSecs(*date, *time),
                                                 d->m_timeZone,
                                                 QDateTimePrivate::UnknownDaylightTime,
@@ -5094,7 +5105,8 @@ QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, const QTimeZone &timeZone
 {
     QDateTime dt;
     dt.setTimeZone(timeZone);
-    dt.setMSecsSinceEpoch(msecs);
+    if (timeZone.isValid())
+        dt.setMSecsSinceEpoch(msecs);
     return dt;
 }
 
diff --git a/src/corelib/time/qdatetimeparser.cpp b/src/corelib/time/qdatetimeparser.cpp
index 74db2bdfd5..61214b0c7e 100644
--- a/src/corelib/time/qdatetimeparser.cpp
+++ b/src/corelib/time/qdatetimeparser.cpp
@@ -1363,7 +1363,7 @@ QDateTimeParser::scanString(const QDateTime &defaultValue,
     // given date (which might be a spring-forward, skipping an hour).
     if (parserType == QVariant::DateTime && !(isSet & HourSectionMask) && !when.isValid()) {
         qint64 msecs = when.toMSecsSinceEpoch();
-        // Fortunately, that gets a useful answer ...
+        // Fortunately, that gets a useful answer, even though when is invalid ...
         const QDateTime replace =
 #if QT_CONFIG(timezone)
             tspec == Qt::TimeZone