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Take account of single-transition hacks in MS time-zone APIs

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When a year contains a real change of standard time without any DST,
MS's APIs still claim to have both a DST start and a DST end; one of
them is bogus and positioned on the start (or end) of the year,
producing no change in offset from the end of the previous (or into
the start of the next) year.  So code round that.

Task-number: QTBUG-42021
Change-Id: Ieb6161cfb77db8a57dc181097f117316f9d1c13c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2017-10-27 18:41:55 +02:00
parent 88d5ba5409
commit 68bcccac22
2 changed files with 106 additions and 17 deletions
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2
src/corelib/tools/qtimezoneprivate_p.h
View File

@ -432,7 +432,7 @@ public:
private:
void init(const QByteArray &ianaId);
QTimeZonePrivate::Data ruleToData(const QWinTransitionRule &rule, qint64 atMSecsSinceEpoch,
QTimeZone::TimeType type) const;
QTimeZone::TimeType type, bool fakeDst = false) const;
QByteArray m_windowsId;
QString m_displayName;

121
src/corelib/tools/qtimezoneprivate_win.cpp
View File

@ -401,14 +401,82 @@ struct TransitionTimePair
{
// Transition times after the epoch, in ms:
qint64 std, dst;
TransitionTimePair(const QWinTimeZonePrivate::QWinTransitionRule &rule, int year)
// If either is invalidMSecs(), which shall then be < the other, there is no
// DST and the other describes a change in actual standard offset.
TransitionTimePair(const QWinTimeZonePrivate::QWinTransitionRule &rule,
int year, int oldYearOffset)
// The local time in Daylight Time of the switch to Standard Time
: std(calculateTransitionForYear(rule.standardTimeRule, year,
rule.standardTimeBias + rule.daylightTimeBias)),
// The local time in Standard Time of the switch to Daylight Time
dst(calculateTransitionForYear(rule.daylightTimeRule, year, rule.standardTimeBias))
{}
{
/*
Check for potential "fake DST", used by MS's APIs because the
TIME_ZONE_INFORMATION spec either expresses no transitions in the
year, or expresses a transition of each kind, even if standard time
did change in a year with no DST. We've seen year-start fake-DST
(whose offset matches prior standard offset, in which the previous
year ended); and conjecture that similar might be used at a year-end.
(This might be used for a southern-hemisphere zone, where the start of
the year usually is in DST, when applicable.) Note that, here, wDay
identifies an instance of a given day-of-week in the month, with 5
meaning last.
Either the alleged standardTimeRule or the alleged daylightTimeRule
may be faked; either way, the transition is actually a change to the
current standard offset; but the unfaked half of the rule contains the
useful bias data, so we have to go along with its lies.
Example: Russia/Moscow
Format: -bias +( -stdBias, stdDate | -dstBias, dstDate ) notes
Last year of DST, 2010: 180 +( 0, 0-10-5 3:0 | 60, 0-3-5 2:0 ) normal DST
Zone change in 2011: 180 +( 0, 0-1-1 0:0 | 60 0-3-5 2:0 ) fake DST at transition
Fixed standard in 2012: 240 +( 0, 0-0-0 0:0 | 60, 0-0-0 0:0 ) standard time years
Zone change in 2014: 180 +( 0, 0-10-5 2:0 | 60, 0-1-1 0:0 ) fake DST at year-start
The last of these is missing on Win7 VMs (too old to know about it).
*/
if (rule.daylightTimeRule.wMonth == 1 && rule.daylightTimeRule.wDay == 1) {
// Fake "DST transition" at start of year producing the same offset as
// previous year ended in.
if (rule.standardTimeBias + rule.daylightTimeBias == oldYearOffset)
dst = QTimeZonePrivate::invalidMSecs();
} else if (rule.daylightTimeRule.wMonth == 12 && rule.daylightTimeRule.wDay > 3) {
// Similar, conjectured, for end of year, not changing offset.
if (rule.daylightTimeBias == 0)
dst = QTimeZonePrivate::invalidMSecs();
}
if (rule.standardTimeRule.wMonth == 1 && rule.standardTimeRule.wDay == 1) {
// Fake "transition out of DST" at start of year producing the same
// offset as previous year ended in.
if (rule.standardTimeBias == oldYearOffset)
std = QTimeZonePrivate::invalidMSecs();
} else if (rule.standardTimeRule.wMonth == 12 && rule.standardTimeRule.wDay > 3) {
// Similar, conjectured, for end of year, not changing offset.
if (rule.daylightTimeBias == 0)
std = QTimeZonePrivate::invalidMSecs();
}
}
bool fakesDst() const
{
return std == QTimeZonePrivate::invalidMSecs()
|| dst == QTimeZonePrivate::invalidMSecs();
}
};
int yearEndOffset(const QWinTimeZonePrivate::QWinTransitionRule &rule, int year)
{
int offset = rule.standardTimeBias;
// Only needed to help another TransitionTimePair work out year + 1's start
// offset; and the oldYearOffset we use only affects an alleged transition
// at the *start* of this year, so it doesn't matter if we guess wrong here:
TransitionTimePair pair(rule, year, offset);
if (pair.dst > pair.std)
offset += rule.daylightTimeBias;
return offset;
}
} // anonymous namespace
static QLocale::Country userCountry()
@ -665,18 +733,22 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::data(qint64 forMSecsSinceEpoch) cons
if (rule.standardTimeRule.wMonth > 0 || rule.daylightTimeRule.wMonth > 0) {
const int endYear = qMax(rule.startYear, year - 1);
while (year >= endYear) {
const TransitionTimePair pair(rule, year);
const int newYearOffset = (year <= rule.startYear && ruleIndex > 0)
? yearEndOffset(m_tranRules.at(ruleIndex - 1), year - 1)
: yearEndOffset(rule, year - 1);
const TransitionTimePair pair(rule, year, newYearOffset);
bool isDst = false;
if (pair.std <= forMSecsSinceEpoch) {
if (pair.std != invalidMSecs() && pair.std <= forMSecsSinceEpoch) {
isDst = pair.std < pair.dst && pair.dst <= forMSecsSinceEpoch;
} else if (pair.dst <= forMSecsSinceEpoch) {
} else if (pair.dst != invalidMSecs() && pair.dst <= forMSecsSinceEpoch) {
isDst = true;
} else {
--year; // Try an earlier year for this rule (once).
continue;
}
return ruleToData(rule, forMSecsSinceEpoch,
isDst ? QTimeZone::DaylightTime : QTimeZone::StandardTime);
isDst ? QTimeZone::DaylightTime : QTimeZone::StandardTime,
pair.fakesDst());
}
// Fell off start of rule, try previous rule.
} else {
@ -711,21 +783,28 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
year = rule.startYear; // Seek first transition in this rule.
const int endYear = ruleIndex + 1 < m_tranRules.count()
? qMin(m_tranRules.at(ruleIndex + 1).startYear, year + 2) : (year + 2);
int newYearOffset = (year <= rule.startYear && ruleIndex > 0)
? yearEndOffset(m_tranRules.at(ruleIndex - 1), year - 1)
: yearEndOffset(rule, year - 1);
while (year < endYear) {
const TransitionTimePair pair(rule, year);
const TransitionTimePair pair(rule, year, newYearOffset);
bool isDst = false;
Q_ASSERT(invalidMSecs() <= afterMSecsSinceEpoch); // invalid is min qint64
if (pair.std > afterMSecsSinceEpoch) {
isDst = pair.std > pair.dst && pair.dst > afterMSecsSinceEpoch;
} else if (pair.dst > afterMSecsSinceEpoch) {
isDst = true;
} else {
newYearOffset = rule.standardTimeBias;
if (pair.dst > pair.std)
newYearOffset += rule.daylightTimeBias;
++year; // Try a later year for this rule (once).
continue;
}
if (isDst)
return ruleToData(rule, pair.dst, QTimeZone::DaylightTime);
return ruleToData(rule, pair.std, QTimeZone::StandardTime);
return ruleToData(rule, pair.dst, QTimeZone::DaylightTime, pair.fakesDst());
return ruleToData(rule, pair.std, QTimeZone::StandardTime, pair.fakesDst());
}
// Fell off end of rule, try next rule.
} // else: no transition during rule's period
@ -744,19 +823,22 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::previousTransition(qint64 beforeMSec
if (rule.standardTimeRule.wMonth > 0 || rule.daylightTimeRule.wMonth > 0) {
const int endYear = qMax(rule.startYear, year - 1);
while (year >= endYear) {
const TransitionTimePair pair(rule, year);
const int newYearOffset = (year <= rule.startYear && ruleIndex > 0)
? yearEndOffset(m_tranRules.at(ruleIndex - 1), year - 1)
: yearEndOffset(rule, year - 1);
const TransitionTimePair pair(rule, year, newYearOffset);
bool isDst = false;
if (pair.std < beforeMSecsSinceEpoch) {
if (pair.std != invalidMSecs() && pair.std < beforeMSecsSinceEpoch) {
isDst = pair.std < pair.dst && pair.dst < beforeMSecsSinceEpoch;
} else if (pair.dst < beforeMSecsSinceEpoch) {
} else if (pair.dst != invalidMSecs() && pair.dst < beforeMSecsSinceEpoch) {
isDst = true;
} else {
--year; // Try an earlier year for this rule (once).
continue;
}
if (isDst)
return ruleToData(rule, pair.dst, QTimeZone::DaylightTime);
return ruleToData(rule, pair.std, QTimeZone::StandardTime);
return ruleToData(rule, pair.dst, QTimeZone::DaylightTime, pair.fakesDst());
return ruleToData(rule, pair.std, QTimeZone::StandardTime, pair.fakesDst());
}
// Fell off start of rule, try previous rule.
} // else: no transition during rule's period
@ -798,12 +880,19 @@ QList<QByteArray> QWinTimeZonePrivate::availableTimeZoneIds() const
QTimeZonePrivate::Data QWinTimeZonePrivate::ruleToData(const QWinTransitionRule &rule,
qint64 atMSecsSinceEpoch,
QTimeZone::TimeType type) const
QTimeZone::TimeType type,
bool fakeDst) const
{
Data tran = invalidData();
tran.atMSecsSinceEpoch = atMSecsSinceEpoch;
tran.standardTimeOffset = rule.standardTimeBias * -60;
if (type == QTimeZone::DaylightTime) {
if (fakeDst) {
tran.daylightTimeOffset = 0;
tran.abbreviation = m_standardName;
// Rule may claim we're in DST when it's actually a standard time change:
if (type == QTimeZone::DaylightTime)
tran.standardTimeOffset += rule.daylightTimeBias * -60;
} else if (type == QTimeZone::DaylightTime) {
tran.daylightTimeOffset = rule.daylightTimeBias * -60;
tran.abbreviation = m_daylightName;
} else {