1 files changed, 38 insertions, 0 deletions
diff --git a/src/qml/jsruntime/qv4dateobject.cpp b/src/qml/jsruntime/qv4dateobject.cpp
index 4e445a73fa..a14c7d9257 100644
--- a/src/qml/jsruntime/qv4dateobject.cpp
+++ b/src/qml/jsruntime/qv4dateobject.cpp
@@ -78,10 +78,21 @@
   QTBUG-75585 for an explanation and possible workarounds.
  */
 #define USE_QTZ_SYSTEM_ZONE
+#elif defined(Q_OS_WASM)
+/*
+    TODO: evaluate using this version of the code more generally, rather than
+    the #else branches of the various USE_QTZ_SYSTEM_ZONE choices. It might even
+    work better than the timezone variant; experiments needed.
+*/
+// Kludge around the lack of time-zone info using QDateTime.
+// It uses localtime() and friends to determine offsets from UTC.
+#define USE_QDT_LOCAL_TIME
 #endif
 
 #ifdef USE_QTZ_SYSTEM_ZONE
 #include <QtCore/QTimeZone>
+#elif defined(USE_QDT_LOCAL_TIME)
+// QDateTime already included above
 #else
 #  ifdef Q_OS_WIN
 #    include <windows.h>
@@ -356,6 +367,7 @@ static inline double MakeDate(double day, double time)
   mean a whole day of DST offset for some zones, that have crossed the
   international date line.  This shall confuse client code.)  The bug report
   against the ECMAScript spec is https://github.com/tc39/ecma262/issues/725
+  and they've now changed the spec so that the following conforms to it ;^>
 */
 
 static inline double DaylightSavingTA(double t, double localTZA) // t is a UTC time
@@ -363,6 +375,12 @@ static inline double DaylightSavingTA(double t, double localTZA) // t is a UTC t
     return QTimeZone::systemTimeZone().offsetFromUtc(
         QDateTime::fromMSecsSinceEpoch(qint64(t), Qt::UTC)) * 1e3 - localTZA;
 }
+#elif defined(USE_QDT_LOCAL_TIME)
+static inline double DaylightSavingTA(double t, double localTZA) // t is a UTC time
+{
+    return QDateTime::fromMSecsSinceEpoch(qint64(t), Qt::UTC
+        ).toLocalTime().offsetFromUtc() * 1e3 - localTZA;
+}
 #else
 // This implementation fails to take account of past changes in standard offset.
 static inline double DaylightSavingTA(double t, double /*localTZA*/)
@@ -721,6 +739,26 @@ static double getLocalTZA()
     // TODO: QTimeZone::resetSystemTimeZone(), see QTBUG-56899 and comment above.
     // Standard offset, with no daylight-savings adjustment, in ms:
     return QTimeZone::systemTimeZone().standardTimeOffset(QDateTime::currentDateTime()) * 1e3;
+#elif defined(USE_QDT_LOCAL_TIME)
+    QDate today = QDate::currentDate();
+    QDateTime near = today.startOfDay(Qt::LocalTime);
+    // Early out if we're in standard time anyway:
+    if (!near.isDaylightTime())
+        return near.offsetFromUtc() * 1000;
+    int year, month;
+    today.getDate(&year, &month, nullptr);
+    // One of the solstices is probably in standard time:
+    QDate summer(year, 6, 21), winter(year - (month < 7 ? 1 : 0), 12, 21);
+    // But check the one closest to the present by preference, in case there's a
+    // standard time offset change between them:
+    QDateTime far = summer.startOfDay(Qt::LocalTime);
+    near = winter.startOfDay(Qt::LocalTime);
+    if (month > 3 && month < 10)
+        near.swap(far);
+    bool isDst = near.isDaylightTime();
+    if (isDst && far.isDaylightTime()) // Permanent DST, probably an hour west:
+        return (qMin(near.offsetFromUtc(), far.offsetFromUtc()) - 3600) * 1000;
+    return (isDst ? far : near).offsetFromUtc() * 1000;
 #else
 #  ifdef Q_OS_WIN
     TIME_ZONE_INFORMATION tzInfo;