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Refine handling of wMonth checks in QWinTimeZonePrivate

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The MS API documents that the two TIME_ZONE_INFORMATION date fields
either both have wMonth clear (when there is no DST) or both have it
set (for each part of a DST pair).  This rule is followed even when
there's a standard time change without DST, with perverse results I'll
deal with in a later commit.  Add code in init() to verify the rule is
followed and qWarning() if not.

A year with no transitions doesn't imply no earlier or later year has
transitions, so don't give up on searches for transitions because of
it.  Also fix a potential uninitialized variable bug, related to
data() breaking out of a loop on such a year.

Change-Id: I1ad86c07e54b2eb835a2e02d18dc64022f52a0d9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2017-10-27 16:40:46 +02:00
parent 81ad5bc838
commit a99c773972
1 changed files with 28 additions and 6 deletions
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34
src/corelib/tools/qtimezoneprivate_win.cpp
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@ -491,6 +491,7 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
m_id = ianaId;
}
bool badMonth = false; // Only warn once per zone, if at all.
if (!m_windowsId.isEmpty()) {
#ifdef QT_USE_REGISTRY_TIMEZONE
// Open the base TZI for the time zone
@ -518,6 +519,14 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
// Don't repeat a recurrent rule:
&& (m_tranRules.isEmpty()
|| !isSameRule(m_tranRules.last(), rule))) {
if (!badMonth
&& (rule.standardTimeRule.wMonth == 0)
!= (rule.daylightTimeRule.wMonth == 0)) {
badMonth = true;
qWarning("MS registry TZ API violated its wMonth constraint;"
"this may cause mistakes for %s from %d",
ianaId.constData(), year);
}
rule.startYear = m_tranRules.isEmpty() ? MIN_YEAR : year;
m_tranRules.append(rule);
}
@ -553,6 +562,14 @@ void QWinTimeZonePrivate::init(const QByteArray &ianaId)
// Don't repeat a recurrent rule
&& (m_tranRules.isEmpty()
|| !isSameRule(m_tranRules.last(), rule))) {
if (!badMonth
&& (rule.standardTimeRule.wMonth == 0)
!= (rule.daylightTimeRule.wMonth == 0)) {
badMonth = true;
qWarning("MS dynamic TZ API violated its wMonth constraint;"
"this may cause mistakes for %s from %d",
ianaId.constData(), year);
}
rule.startYear = m_tranRules.isEmpty() ? MIN_YEAR : year;
m_tranRules.append(rule);
}
@ -650,6 +667,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::data(qint64 forMSecsSinceEpoch) cons
qint64 second;
qint64 next = maxMSecs();
TransitionTimePair pair;
Q_ASSERT(next != pair.dst); // so break on first iteration gets standard time
QWinTransitionRule rule;
do {
// Convert the transition rules into msecs for the year we want to try
@ -712,9 +730,11 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
do {
// Convert the transition rules into msecs for the year we want to try
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If no transition rules to calculate then no next transition
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0)
return invalidData();
// If there's no transition this year, check for a later year:
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0) {
++year;
continue;
}
pair = TransitionTimePair(rule, year);
// Find the first and second transition for the year
if (pair.std < pair.dst) {
@ -762,9 +782,11 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::previousTransition(qint64 beforeMSec
do {
// Convert the transition rules into msecs for the year we want to try
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If no transition rules to calculate then no previous transition
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0)
return invalidData();
// If there's no transition this year, check for an earlier year:
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0) {
--year;
continue;
}
pair = TransitionTimePair(rule, year);
if (pair.std < pair.dst) {
first = pair.std;