QTime: restore Qt3 compatibility in the QDataStream operators

A Qt5 program writing a null QTime() using setVersion(QDataStream::Qt_3_3),
and then a Qt3 program reading that, would lead to a weird QTime,
with isNull=false, isValid=false, hour=1193, minute=2, second=47, ms=295.

This commit restores interoperability, by writing out the expected value
(0) for a null QTime rather than the -1 value used by Qt4 and Qt5.

Change-Id: Icde468a8f6fc9434ef7018296725819b44d672af
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index fb679e56c5..e6d0b97836 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -4759,7 +4759,12 @@ QDataStream &operator>>(QDataStream &in, QDate &date)
 
 QDataStream &operator<<(QDataStream &out, const QTime &time)
 {
-    return out << quint32(time.mds);
+    if (out.version() >= QDataStream::Qt_4_0) {
+        return out << quint32(time.mds);
+    } else {
+        // Qt3 had no support for reading -1, QTime() was valid and serialized as 0
+        return out << quint32(time.isNull() ? 0 : time.mds);
+    }
 }
 
 /*!
@@ -4774,7 +4779,12 @@ QDataStream &operator>>(QDataStream &in, QTime &time)
 {
     quint32 ds;
     in >> ds;
-    time.mds = int(ds);
+    if (in.version() >= QDataStream::Qt_4_0) {
+        time.mds = int(ds);
+    } else {
+        // Qt3 would write 0 for a null time
+        time.mds = (ds == 0) ? QTime::NullTime : int(ds);
+    }
     return in;
 }