QDateTime: disambiguate times in a zone transition

Previously, requesting a time that got repeated - on the given date,
due to a fall-back transition - would get one of the two repeats,
giving the caller (no hint that there was a choice and) no way to
select the other. Add a flags parameter that captures the available
ways to resolve such ambiguity or select a suitable time near a gap.

Add such a parameter to relevant QDateTime methods, including
constructors, to enable callers to indicate their preference in the
same way. This replaces DST-hint parameters in various internal
functions, including QTimeZonePrivate's dataForLocalTime(). Adapted
tst_QDateTime to test the new feature.

Adapt to gap-times no longer being invalid (by default; or, when they
are, no longer having a useful toMSecsSinceEpoch() value). Instead,
they don't match what was asked for. Amend documentation to reflect
that. Most of the code change for this is to QDTParser and QDTEdit.

[ChangeLog][QtCore][QDateTime] Added a TransitionResolution parameter
to various QDateTime methods to enable the caller to indicate, when
the indicated datetime falls in a time-zone transition, which side of
the transition to fall or whether to produce an invalid result.

[ChangeLog][QtCore][Possibly Significant Behavior Change] When
QDateTime is instantiated for a combination of date and time that was
skipped, by local time or a time-zone, for example during a
spring-forward DST transition, the result is no longer marked invalid.
Whether the selected nearby date-time is before or after the skipped
interval may have changed on some platforms; unless overridden by an
explicit TransitionResolution, it is now a date-time as long after the
previous day's noon as a naive reading of the requested date and time
would expect. This was the prior behavior at least on Linux.

Fixes: QTBUG-79923
Change-Id: I11d5339abef9e7125c4e0dc95a09a7cd4f169dab
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index 04af737add..bb3dca62a1 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -618,6 +618,19 @@ QStringView QXmlStreamAttributes::value(QLatin1StringView qualifiedName) const
 
 #if QT_CORE_REMOVED_SINCE(6, 7)
 
+#include "qdatetime.h"
+
+QDateTime::QDateTime(QDate date, QTime time, const QTimeZone &timeZone)
+    : QDateTime(date, time, timeZone, TransitionResolution::LegacyBehavior) {}
+QDateTime::QDateTime(QDate date, QTime time)
+    : QDateTime(date, time, TransitionResolution::LegacyBehavior) {}
+void QDateTime::setDate(QDate date) { setDate(date, TransitionResolution::LegacyBehavior); }
+void QDateTime::setTime(QTime time) { setTime(time, TransitionResolution::LegacyBehavior); }
+void QDateTime::setTimeZone(const QTimeZone &toZone)
+{
+    setTimeZone(toZone, TransitionResolution::LegacyBehavior);
+}
+
 #if defined(Q_OS_ANDROID)
 
 #include "qjniobject.h"