Properly handle negative years when printing JS Dates to strings.

JavaScript knows a year 0. That is correctly translated into QDateTime
terms when creating a Date object, but it's not correctly translated
back when converting the JavaScript date to a string.

Task-number: QTBUG-29491
Change-Id: I46b200a144434187656d08e87f422f97523acd0e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

src/qml/jsruntime/qv4dateobject.cpp

@@ -557,7 +557,13 @@ static inline QString ToString(double t)
 {
     if (std::isnan(t))
         return QStringLiteral("Invalid Date");
-    QString str = ToDateTime(t, Qt::LocalTime).toString() + QStringLiteral(" GMT");
+    QDateTime dateTime = ToDateTime(t, Qt::LocalTime);
+
+    // JavaScript knows a year 0, while QDateTime doesn't. So, in order to show the right date we
+    // have to add a year to negative ones here.
+    if (dateTime.date().year() < 0)
+        dateTime = dateTime.addYears(1);
+    QString str = dateTime.toString() + QStringLiteral(" GMT");
     double tzoffset = LocalTZA + DaylightSavingTA(t);
     if (tzoffset) {
         int hours = static_cast<int>(::fabs(tzoffset) / 1000 / 60 / 60);

tests/auto/qml/qqmlecmascript/data/negativeyear.qml

@@ -0,0 +1,8 @@
+import QtQuick 2.0
+import Qt.test 1.0
+
+Item {
+    function check_negative() {
+        return "result: " + new Date(-2000, 0, 1);
+    }
+}

tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp

@@ -200,6 +200,7 @@ private slots:
     void sequenceSort();
     void dateParse();
     void utcDate();
+    void negativeYear();
     void qtbug_22464();
     void qtbug_21580();
     void singleV8BindingDestroyedDuringEvaluation();
@@ -7378,6 +7379,22 @@ void tst_qqmlecmascript::utcDate()
     QVERIFY(q.toBool() == true);
 }
 
+void tst_qqmlecmascript::negativeYear()
+{
+    QQmlComponent component(&engine, testFileUrl("negativeyear.qml"));
+
+    QObject *object = component.create();
+    if (object == 0)
+        qDebug() << component.errorString();
+    QVERIFY(object != 0);
+
+    QVariant q;
+    QMetaObject::invokeMethod(object, "check_negative",
+                              Q_RETURN_ARG(QVariant, q));
+    // Strip the timezone. It should be irrelevant as the date was created with the same one.
+    QCOMPARE(q.toString().left(32), QStringLiteral("result: Mon Jan 1 00:00:00 -2000"));
+}
+
 void tst_qqmlecmascript::concatenatedStringPropertyAccess()
 {
     QQmlComponent component(&engine, testFileUrl("concatenatedStringPropertyAccess.qml"));