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Reland "Implement a new spec for timezone offset calculation"
This is a reland of dbdede0 after a webkit layout test (geolocation-api/timestamp.html) was fixed by https://chromium-review.googlesource.com/c/chromium/src/+/994343 . Original change's description: > Implement a new spec for timezone offset calculation > > tc39/ecma262#778 was recently merged > to Ecma 262. > > It changes the way to convert between "local time" and UTC in such > a way that it'd work for all timezones whether or not there has > been any change in the timezone offset of the standard time. For > instance, Europe/Moscow and some parts of US state of Indiana have > changed the standard (non-DST) timezone offset a few times. The > previous spec assumes that the the standard timezone offset is > constant, but the new spec take into account the offset change > history. > > In addition, it specifies a new way to calculate the timezone > offset during a timezone transition (either in and > out of DST or timezone offset shift). > > During a negative transition (e.g. fall backward / getting > out of DST), repeated times are to be interpreted as if the > offset before the transition is in effect. > > During a positive transition (e.g. spring forward / getting > into DST), skipped times are to be treated similarly. That > is, they are to be interpreted as if the offset before the > transition is in effect. > > With icu-timezone-data, v8 is compliant to the new spec for the > past and the future as well as now whether or not the standard > timezone offset of a given timezone has changed over time > (e.g. Europe/Moscow, Pacific/Apia). With icu-timezone-data, > Australia/Lord_Howe (30 minute DST change) also works per spec. > > Without icu-timezone-data, it works only for timezones of which > the standard timezone offset is the same as the current offset > (e.g. most North American timezones other than parts of Indiana) > and of which the DST shift is an hour. For instance, it doesn't work > for Europe/Moscow in 2010 when the standard timezone offset was > +4h because the current (2018) standard timezone offset is +3h. Neither > does it for Lord Howe in Australia with the DST shift of 0.5 hr. > > This CL used to require one of the two ICU CLs below, but not > any more. > > https://chromium-review.googlesource.com/c/chromium/deps/icu/+/572652 > https://chromium-review.googlesource.com/851265 (a proposed CL to the > upstream ICU). > > Bug: v8:3547,chromium:417640,v8:5714 > Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng > Change-Id: Ib162295da5bee31b2390bd0918157014aebd3e33 > Reviewed-on: https://chromium-review.googlesource.com/572148 > Commit-Queue: Jungshik Shin <jshin@chromium.org> > Reviewed-by: Daniel Ehrenberg <littledan@chromium.org> > Reviewed-by: Michael Lippautz <mlippautz@chromium.org> > Cr-Commit-Position: refs/heads/master@{#52332} Bug: v8:3547, chromium:417640, v8:5714 Change-Id: I47536c111143f75e3cfeecf5d9761c43a98a10f5 Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng;master.tryserver.blink:linux_trusty_blink_rel Reviewed-on: https://chromium-review.googlesource.com/995971 Commit-Queue: Jungshik Shin <jshin@chromium.org> Reviewed-by: Clemens Hammacher <clemensh@chromium.org> Cr-Commit-Position: refs/heads/master@{#52372}
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