1 files changed, 38 insertions, 22 deletions

diff --git a/src/corelib/time/qtimezoneprivate_icu.cpp b/src/corelib/time/qtimezoneprivate_icu.cpp
index c071e7d549..1a3baa70d0 100644
--- a/src/corelib/time/qtimezoneprivate_icu.cpp
+++ b/src/corelib/time/qtimezoneprivate_icu.cpp
@@ -153,7 +153,7 @@ static QTimeZonePrivate::Data ucalTimeZoneTransition(UCalendar *m_ucal,
                                                      UTimeZoneTransitionType type,
                                                      qint64 atMSecsSinceEpoch)
 {
-    QTimeZonePrivate::Data tran = QTimeZonePrivate::invalidData();
+    QTimeZonePrivate::Data tran;
 
     // Clone the ucal so we don't change the shared object
     UErrorCode status = U_ZERO_ERROR;
@@ -254,8 +254,8 @@ QIcuTimeZonePrivate::QIcuTimeZonePrivate()
 QIcuTimeZonePrivate::QIcuTimeZonePrivate(const QByteArray &ianaId)
     : m_ucal(nullptr)
 {
-    // Need to check validity here as ICu will create a GMT tz if name is invalid
-    if (availableTimeZoneIds().contains(ianaId))
+    // ICU misleadingly maps invalid IDs to GMT.
+    if (isTimeZoneIdAvailable(ianaId))
         init(ianaId);
 }
 
@@ -301,28 +301,25 @@ QString QIcuTimeZonePrivate::displayName(QTimeZone::TimeType timeType,
                                          QTimeZone::NameType nameType,
                                          const QLocale &locale) const
 {
-    // Return standard offset format name as ICU C api doesn't support it yet
+    // Base class has handled OffsetName if we came via the other overload.
     if (nameType == QTimeZone::OffsetName) {
-        const Data nowData = data(QDateTime::currentMSecsSinceEpoch());
-        // We can't use transitions reliably to find out right dst offset
-        // Instead use dst offset api to try get it if needed
+        int offset = standardTimeOffset(QDateTime::currentMSecsSinceEpoch());
+        // We can't use transitions reliably to find out right DST offset.
+        // Instead use DST offset API to try to get it, when needed:
         if (timeType == QTimeZone::DaylightTime)
-            return isoOffsetFormat(nowData.standardTimeOffset + ucalDaylightOffset(m_id));
-        else
-            return isoOffsetFormat(nowData.standardTimeOffset);
+            offset += ucalDaylightOffset(m_id);
+        // This is only valid for times since the most recent standard offset
+        // change; for earlier times, caller must use the other overload.
+
+        // Use our own formating for offset names (ICU C API doesn't support it
+        // and we may as well be self-consistent anyway).
+        return isoOffsetFormat(offset);
     }
+    // Technically this may be suspect, if locale isn't QLocale(), since that's
+    // what we used when constructing m_ucal; does ICU cope with inconsistency ?
     return ucalTimeZoneDisplayName(m_ucal, timeType, nameType, locale.name());
 }
 
-QString QIcuTimeZonePrivate::abbreviation(qint64 atMSecsSinceEpoch) const
-{
-    // TODO No ICU API, use short name instead
-    if (isDaylightTime(atMSecsSinceEpoch))
-        return displayName(QTimeZone::DaylightTime, QTimeZone::ShortName, QLocale());
-    else
-        return displayName(QTimeZone::StandardTime, QTimeZone::ShortName, QLocale());
-}
-
 int QIcuTimeZonePrivate::offsetFromUtc(qint64 atMSecsSinceEpoch) const
 {
     int stdOffset = 0;
@@ -387,7 +384,7 @@ bool QIcuTimeZonePrivate::isDaylightTime(qint64 atMSecsSinceEpoch) const
 QTimeZonePrivate::Data QIcuTimeZonePrivate::data(qint64 forMSecsSinceEpoch) const
 {
     // Available in ICU C++ api, and draft C api in v50
-    QTimeZonePrivate::Data data = invalidData();
+    QTimeZonePrivate::Data data;
 #if U_ICU_VERSION_MAJOR_NUM >= 50
     data = ucalTimeZoneTransition(m_ucal, UCAL_TZ_TRANSITION_PREVIOUS_INCLUSIVE,
                                   forMSecsSinceEpoch);
@@ -420,7 +417,7 @@ QTimeZonePrivate::Data QIcuTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
     return ucalTimeZoneTransition(m_ucal, UCAL_TZ_TRANSITION_NEXT, afterMSecsSinceEpoch);
 #else
     Q_UNUSED(afterMSecsSinceEpoch);
-    return invalidData();
+    return {};
 #endif
 }
 
@@ -431,7 +428,7 @@ QTimeZonePrivate::Data QIcuTimeZonePrivate::previousTransition(qint64 beforeMSec
     return ucalTimeZoneTransition(m_ucal, UCAL_TZ_TRANSITION_PREVIOUS, beforeMSecsSinceEpoch);
 #else
     Q_UNUSED(beforeMSecsSinceEpoch);
-    return invalidData();
+    return {};
 #endif
 }
 
@@ -442,6 +439,25 @@ QByteArray QIcuTimeZonePrivate::systemTimeZoneId() const
     return ucalDefaultTimeZoneId();
 }
 
+bool QIcuTimeZonePrivate::isTimeZoneIdAvailable(const QByteArray &ianaId) const
+{
+    const QString ianaStr = QString::fromUtf8(ianaId);
+    const UChar *const name = reinterpret_cast<const UChar *>(ianaStr.constData());
+    // We are not interested in the value, but we have to pass something.
+    // No known IANA zone name is (up to 2023) longer than 30 characters.
+    constexpr size_t size = 64;
+    UChar buffer[size];
+
+    // TODO: convert to ucal_getIanaTimeZoneID(), new draft in ICU 74, once we
+    // can rely on its availability, assuming it works the same once not draft.
+    UErrorCode status = U_ZERO_ERROR;
+    UBool isSys = false;
+    // Returns the length of the IANA zone name (but we don't care):
+    ucal_getCanonicalTimeZoneID(name, ianaStr.size(), buffer, size, &isSys, &status);
+    // We're only interested if the result is a "system" (i.e. IANA) ID:
+    return isSys;
+}
+
 QList<QByteArray> QIcuTimeZonePrivate::availableTimeZoneIds() const
 {
     UErrorCode status = U_ZERO_ERROR;