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Return a more useful date-time on parser failure in spring-forward gap

Browse Source 
Up to 5.15.0, QDateTime::fromString(), when parsing a string that
matched the format but represented a date-time in a spring-forward's
gap, would return an invalid date-time object that represented a "best
shot" date-time, correcting the error in the string as best it could.

In 5.15, in order to handle time-spec information correctly, we
adapted the date-time parser to have a fromString() variant that
parsed a date-time as a whole, rather than as a date and a time; as a
result, QDTP::fromString() now returns false and QDT::fromString()
returned a default-constructed instance instead of the invalid
date-time that QDTP had produced.

Amend 76054516047d8efb8529443830bb4d9ddf01010f to restore the prior
behavior of returning the invalid date-time object from QDTP instead
of a default-constructed invalid date-time. Also document what this
implies for the caller's ability to recover from the situation, if a
best shot result is better than nothing.

[ChangeLog][QtCore][QDateTime] Restored pre-5.15.0 behavior when
parsing a date-time from a string (and document what it implies): if
the string has the right form but represents a date-time that was
skipped by a time-zone transition (e.g. a DST spring-forward), the
invalid date-time object returned can, none the less, be used to
recover a near-by date-time that may be more useful in some cases.
From 5.15.0 to 5.15.2 and in 6.0.0, a default-constructed QDateTime
was returned in place of this more informative invalid date-time.

Task-number: QTBUG-88633
Change-Id: If0b439038d5fe48eefb951c62f3aae2933bb5651
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 3a4115d1236bc78dda078657883283cc92df8e8a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Edward Welbourne 2020-11-25 12:18:49 +01:00 committed by Qt Cherry-pick Bot
parent f27623c2ed
commit d3397c92a0
2 changed files with 15 additions and 4 deletions
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9
src/corelib/text/qlocale.cpp
View File

@ -2265,7 +2265,12 @@ QDate QLocale::toDate(const QString &string, const QString &format, QCalendar ca
\note The month and day names used must be given in the user's local
language.
If the string could not be parsed, returns an invalid QDateTime.
If the string could not be parsed, returns an invalid QDateTime. If the
string can be parsed and represents an invalid date-time (e.g. in a gap
skipped by a time-zone transition), an invalid QDateTime is returned, whose
toMSecsSinceEpoch() represents a near-by date-time that is valid. Passing
that to fromMSecsSinceEpoch() will produce a valid date-time that isn't
faithfully represented by the string parsed.
\sa dateTimeFormat(), toTime(), toDate(), QDateTime::fromString()
*/
@ -2285,7 +2290,7 @@ QDateTime QLocale::toDateTime(const QString &string, const QString &format, QCal
QDateTimeParser dt(QMetaType::QDateTime, QDateTimeParser::FromString, cal);
dt.setDefaultLocale(*this);
if (dt.parseFormat(format) && dt.fromString(string, &datetime))
if (dt.parseFormat(format) && (dt.fromString(string, &datetime) || !datetime.isValid()))
return datetime;
#else
Q_UNUSED(string);

10
src/corelib/time/qdatetime.cpp
View File

@ -4977,7 +4977,13 @@ QDateTime QDateTime::fromString(QStringView string, Qt::DateFormat format)
\snippet code/src_corelib_time_qdatetime.cpp 12
If the format is not satisfied, an invalid QDateTime is returned.
If the format is not satisfied, an invalid QDateTime is returned. If the
format is satisfied but \a string represents an invalid date-time (e.g. in a
gap skipped by a time-zone transition), an invalid QDateTime is returned,
whose toMSecsSinceEpoch() represents a near-by date-time that is
valid. Passing that to fromMSecsSinceEpoch() will produce a valid date-time
that isn't faithfully represented by the string parsed.
The expressions that don't have leading zeroes (d, M, h, m, s, z) will be
greedy. This means that they will use two digits (or three, for z) even if this will
put them outside the range and/or leave too few digits for other
@ -5025,7 +5031,7 @@ QDateTime QDateTime::fromString(const QString &string, QStringView format, QCale
QDateTimeParser dt(QMetaType::QDateTime, QDateTimeParser::FromString, cal);
dt.setDefaultLocale(QLocale::c());
if (dt.parseFormat(format) && dt.fromString(string, &datetime))
if (dt.parseFormat(format) && (dt.fromString(string, &datetime) || !datetime.isValid()))
return datetime;
#else
Q_UNUSED(string);