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Make systemTimeZone() and systemTimeZoneId() consistent

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It's possible, as was (and still is) documented, at least on Windows,
for the backend to determine the system local time zone's properties
but not its IANA ID. (That involves an update to Windows introducing a
Windows zone ID unknown to the CLDR with whose data Qt was compiled.)
Formerly this lead to systemTimeZoneId() and systemTimeZone().id()
being inconsistent. Furthermore, either in this case or when the
system zone can't be determined, passing the return from
systemTimeZoneId() to the constructor got a valid QTimeZone that did
not faithfully represent the system's local time or the return from
systemTimeZone().

[ChangeLog][QtCore][QTimeZone] When unable to determine the IANA ID of
the system's local time zone, QTimeZone::systemTimeZoneId() now
returns empty instead of the "UTC" it formerly, and misleadingly,
returned. Passing the return to the QTimeZone constructor now
consistently produces the same as calling QTimeZone::systemTimeZone(),
whose id() now matches the return from QTimeZone::systemTimeZoneId().
This is independent of whether QTimeZone::systemTimeZone() is valid.

Change-Id: I55bbe3ea407ca38343a09da353d9336708747bf1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2023-09-14 18:00:08 +02:00
parent 8e0bf6e05b
commit ffe8932ef3
1 changed files with 18 additions and 11 deletions
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29
src/corelib/time/qtimezone.cpp
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@ -1315,13 +1315,25 @@ QTimeZone::OffsetDataList QTimeZone::transitions(const QDateTime &fromDateTime,
/*! /*!
Returns the current system time zone IANA ID. Returns the current system time zone IANA ID.
On Windows this ID is translated from the Windows ID using an internal Equivalent to calling systemTimeZone().id(), but may bypass some computation
translation table and the user's selected country. As a consequence there to obtain it. Constructing a QTimeZone from the returned byte array will
is a small chance any Windows install may have IDs not known by Qt, in produce the same result as systemTimeZone().
which case "UTC" will be returned.
If the backend is unable to determine the correct system zone, the result is
empty. In this case, systemTimeZone().isValid() is false and a warning is
output if either this method of systemTimeZone() is called.
If the backend is able to determine the correct system zone but not its
name, an empty byte array is returned. For example, on Windows, the system
native ID is converted to an IANA ID - if the system ID isn't known to the
internal translation code, the result shall be empty. In this case,
systemTimeZone().isValid() shall be true.
This method is only available when feature \c timezone is enabled. This method is only available when feature \c timezone is enabled.
\note Prior to Qt 6.7, when the result could not be determined, the
misleading result "UTC" was returned.
\sa systemTimeZone() \sa systemTimeZone()
*/ */
@ -1331,12 +1343,7 @@ QByteArray QTimeZone::systemTimeZoneId()
if (!sys.isEmpty()) if (!sys.isEmpty())
return sys; return sys;
// The system zone, despite the empty ID, may know its real ID anyway: // The system zone, despite the empty ID, may know its real ID anyway:
auto zone = systemTimeZone(); return systemTimeZone().id();
if (zone.isValid() && !zone.id().isEmpty())
return zone.id();
// TODO: "-00:00", meaning "unspecified local zone" in some RFC, may be more apt.
// If all else fails, guess UTC.
return QTimeZonePrivate::utcQByteArray();
} }
/*! /*!
@ -1355,7 +1362,7 @@ QByteArray QTimeZone::systemTimeZoneId()
lack the timezone data relied on by the backend for which Qt was compiled, lack the timezone data relied on by the backend for which Qt was compiled,
it may be invalid. In such a case, a warning is output. it may be invalid. In such a case, a warning is output.
\sa utc(), Initialization, asBackendZone() \sa utc(), Initialization, asBackendZone(), systemTimeZoneId()
*/ */
QTimeZone QTimeZone::systemTimeZone() QTimeZone QTimeZone::systemTimeZone()
{ {