3 ms·

I wonder what happens when a timezone ceases to exist, e.g. what if Paris is renamed to New New York after the British take revenge and take over France.

jitl 2y ago
A timezone changing or being eliminated doesn’t erase the history of that timezone. So you can still use the last definition of such a timezone if the date is still in the future, or use the appropriate definition of the timezone at the time of a date marked in the past.
- williamdclt 2y ago
  > you can still use the last definition of such a timezone if the date is still in the future but that'll possibly give you an incorrect time! If you want to store "8am in Paris on the 2026-01-01", then you store "2026-01-01T08:00:00 Europe/Paris". Great, if Paris decides to change their offset rules, that's fine. Currently, that would be `2026-01-01T08:00:00+01:00` but if Paris decide to ditch DST, it could become `2026-01-01T08:00:00+00:00`. All good, you stored a timezone rather than an offset, so you're decoupled from the timezone->offset changes. But if tomorrow `Europe/Paris` cease to exist, and is replaced with Europe/NewNewYork? The last definition of Europe/Paris would make this date `2026-01-01T08:00:00+01:00`, but if Europe/NewNewYork ditched DST then it wouldn't be 8am for the people living there, it'd be 7am. You're decoupled from the timezone->offset changes, but not from location->timezone changes.
  - jitl 2y ago
    The reason the zones use city names is because city identity is far more stable than national or regional borders. Still, the system can gracefully handle deprecation of a zone name. If Paris is renamed NewNewYork by edict of some new global despot, the IANA will just alias the two names together. See https://github.com/eggert/tz/blob/main/backward https://github.com/eggert/tz/blob/main/backward for all the deprecated zones.
tomhallett 2y ago
Your example of “New X” is spot on, because there was a timezone with that name, “US/Pacific-New”, which was different than “US/Pacific”. Bit of history: it was added to some timezone libraries because there was a bill in congress to add it, but it never passed. I had to fix a bug because users were getting set with that timezone and then other systems/libraries were barfing on it… https://github.com/moment/moment-timezone/issues/498 https://github.com/moment/moment-timezone/issues/498
mason55 2y ago
Here are a couple starting points https://medium.com/servicios-a0/on-solving-the-tzdb-changes-problem-7b9fa8f96b86 https://medium.com/servicios-a0/on-solving-the-tzdb-changes-... https://github.com/tc39/proposal-canonical-tz https://github.com/tc39/proposal-canonical-tz - appropriately to these comments, a proposal to handle tzdb changes, built on top of JS Temporal, includes some great examples of all the ways this can happen
- justingrantjg 2y ago
  > https://github.com/tc39/proposal-canonical-tz https://github.com/tc39/proposal-canonical-tz - appropriately to these comments, a proposal to handle tzdb changes, built on top of JS Temporal, includes some great examples of all the ways this can happen Thanks! I was the co-champion of that proposal. Parts of it were merged into Temporal last year, and other parts are already part of the JS Internationalization (ECMA-402) specification here: https://tc39.es/ecma402/#sec-use-of-iana-time-zone-database https://tc39.es/ecma402/#sec-use-of-iana-time-zone-database
Macha 2y ago
Then Europe/Paris will become an alias for Europe/NewNewYork
- williamdclt 2y ago
  What if England and Germany fight for France, half the country being occupied by Germany using `Europe/Francefurt` and the other half by England using `Europe/NewNewYork`? Then you can't know for sure how to interpret a "Europe/Paris" date without knowing the exact geographical location
  - JW_00000 2y ago
    If I understand [1] correctly, two new zones (or one new one and the old one) would be created in that case. E.g. if Strasbourg would be occupied by Germany in 2027, a new Europe/Strasbourg could be created which has the same rules as Europe/Paris until 2026, and the rules of Europe/Berlin as of 2027. [1] https://en.wikipedia.org/wiki/Tz_database https://en.wikipedia.org/wiki/Tz_database -- By the way, I looked up the time zone in Crimea. > On 29 March 2014, after annexation by Russia, Crimea switched from Eastern European Time (UTC+02:00) to Moscow Time (UTC+04:00 then, subsequently changed to UTC+03:00). [2] Crimea has its own zone in the IANA database, Europe/Simferopol, which was updated in 2014 (and already existed before, as it already used Moscow time from 1994 to 1997). [3] [2] https://en.wikipedia.org/wiki/Time_in_Ukraine https://en.wikipedia.org/wiki/Time_in_Ukraine [3] https://lists.iana.org/hyperkitty/list/tz@iana.org/thread/DSQMDSIJMAERCKJNB2LQF2OZHO5EA72H/#VJJQUQZCUDSMM2RIXBZB75IROWQT2UOF https://lists.iana.org/hyperkitty/list/tz@iana.org/thread/DS...; https://github.com/eggert/tz/commit/bb203f1bb0b6cd4bb2b08f2560a3e564a5614c59 https://github.com/eggert/tz/commit/bb203f1bb0b6cd4bb2b08f25...; https://github.com/eggert/tz/blob/bb203f1bb0b6cd4bb2b08f2560a3e564a5614c59/europe#L2942 https://github.com/eggert/tz/blob/bb203f1bb0b6cd4bb2b08f2560...
WorldMaker 2y ago
https://www.icann.org/en/blogs/details/how-time-zones-are-coordinated-13-03-2023-en https://www.icann.org/en/blogs/details/how-time-zones-are-co... Hopefully the British would be kind enough to email the TZ DB group at the IANA (tz@iana.org) a couple years in advance of the legislation to change the name so that the group can get started on collecting the DST rules for Europe/NewNewYork. Some people and devices will probably stick to Europe/Paris out of habit and/or resistance to the change, so the TZ DB would probably be unlikely to remove it, but they may point references from it to Europe/NewNewYork as the new "canonical" name. Plenty of the DB entries are just pointers to other entries already today, for one instance it was decided that America/City and Europe/City maybe is too conflicted a namespace and we see increasingly more "the canonical name is America/State/City" or "the canonical name is Europe/Country/City".
- mikepurvis 2y ago
  As a Canadian, I would love for my timezone to be Americas/Toronto or Americas/Canada/Toronto rather than America/Toronto, but that's pretty far down my register of first world problems.
  - deleted 2y ago
    [deleted]
  - mjevans 2y ago
    How about something like: Sol3/CA/Toronto I'd also like all 50 state capitols (and possibly also their largest city) to exist as E.G. Sol3/US/WA-Olympia and Sol3/US/WA-Seattle (respectively to the above; I don't know Canadian provinces that well) Sol3 is a prefix for the 3rd planet (starting ordinal 1, but anything in the orbit of Sol can be Sol0) in our solar system. It's also nicely short so easy to type out in command lines. Every state _should_ have it's own TZ file, even if it's just an alias. That's a good forward compatible way of allowing the same config to work if future legislative efforts produce or remove timezones. It would also allow E.G. Arizona's non DST timezone to remain correctly configured in some future where the US finally ends the nightmare of DST forever.

jitl 2y ago

A timezone changing or being eliminated doesn’t erase the history of that timezone. So you can still use the last definition of such a timezone if the date is still in the future, or use the appropriate definition of the timezone at the time of a date marked in the past.

williamdclt 2y ago
> you can still use the last definition of such a timezone if the date is still in the future but that'll possibly give you an incorrect time! If you want to store "8am in Paris on the 2026-01-01", then you store "2026-01-01T08:00:00 Europe/Paris". Great, if Paris decides to change their offset rules, that's fine. Currently, that would be `2026-01-01T08:00:00+01:00` but if Paris decide to ditch DST, it could become `2026-01-01T08:00:00+00:00`. All good, you stored a timezone rather than an offset, so you're decoupled from the timezone->offset changes. But if tomorrow `Europe/Paris` cease to exist, and is replaced with Europe/NewNewYork? The last definition of Europe/Paris would make this date `2026-01-01T08:00:00+01:00`, but if Europe/NewNewYork ditched DST then it wouldn't be 8am for the people living there, it'd be 7am. You're decoupled from the timezone->offset changes, but not from location->timezone changes.
- jitl 2y ago
  The reason the zones use city names is because city identity is far more stable than national or regional borders. Still, the system can gracefully handle deprecation of a zone name. If Paris is renamed NewNewYork by edict of some new global despot, the IANA will just alias the two names together. See https://github.com/eggert/tz/blob/main/backward https://github.com/eggert/tz/blob/main/backward for all the deprecated zones.

tomhallett 2y ago

Your example of “New X” is spot on, because there was a timezone with that name, “US/Pacific-New”, which was different than “US/Pacific”. Bit of history: it was added to some timezone libraries because there was a bill in congress to add it, but it never passed. I had to fix a bug because users were getting set with that timezone and then other systems/libraries were barfing on it… https://github.com/moment/moment-timezone/issues/498 https://github.com/moment/moment-timezone/issues/498

mason55 2y ago

Here are a couple starting points https://medium.com/servicios-a0/on-solving-the-tzdb-changes-problem-7b9fa8f96b86 https://medium.com/servicios-a0/on-solving-the-tzdb-changes-... https://github.com/tc39/proposal-canonical-tz https://github.com/tc39/proposal-canonical-tz - appropriately to these comments, a proposal to handle tzdb changes, built on top of JS Temporal, includes some great examples of all the ways this can happen

justingrantjg 2y ago
> https://github.com/tc39/proposal-canonical-tz https://github.com/tc39/proposal-canonical-tz - appropriately to these comments, a proposal to handle tzdb changes, built on top of JS Temporal, includes some great examples of all the ways this can happen Thanks! I was the co-champion of that proposal. Parts of it were merged into Temporal last year, and other parts are already part of the JS Internationalization (ECMA-402) specification here: https://tc39.es/ecma402/#sec-use-of-iana-time-zone-database https://tc39.es/ecma402/#sec-use-of-iana-time-zone-database

Macha 2y ago

Then Europe/Paris will become an alias for Europe/NewNewYork

williamdclt 2y ago
What if England and Germany fight for France, half the country being occupied by Germany using `Europe/Francefurt` and the other half by England using `Europe/NewNewYork`? Then you can't know for sure how to interpret a "Europe/Paris" date without knowing the exact geographical location
- JW_00000 2y ago
  If I understand [1] correctly, two new zones (or one new one and the old one) would be created in that case. E.g. if Strasbourg would be occupied by Germany in 2027, a new Europe/Strasbourg could be created which has the same rules as Europe/Paris until 2026, and the rules of Europe/Berlin as of 2027. [1] https://en.wikipedia.org/wiki/Tz_database https://en.wikipedia.org/wiki/Tz_database -- By the way, I looked up the time zone in Crimea. > On 29 March 2014, after annexation by Russia, Crimea switched from Eastern European Time (UTC+02:00) to Moscow Time (UTC+04:00 then, subsequently changed to UTC+03:00). [2] Crimea has its own zone in the IANA database, Europe/Simferopol, which was updated in 2014 (and already existed before, as it already used Moscow time from 1994 to 1997). [3] [2] https://en.wikipedia.org/wiki/Time_in_Ukraine https://en.wikipedia.org/wiki/Time_in_Ukraine [3] https://lists.iana.org/hyperkitty/list/tz@iana.org/thread/DSQMDSIJMAERCKJNB2LQF2OZHO5EA72H/#VJJQUQZCUDSMM2RIXBZB75IROWQT2UOF https://lists.iana.org/hyperkitty/list/tz@iana.org/thread/DS...; https://github.com/eggert/tz/commit/bb203f1bb0b6cd4bb2b08f2560a3e564a5614c59 https://github.com/eggert/tz/commit/bb203f1bb0b6cd4bb2b08f25...; https://github.com/eggert/tz/blob/bb203f1bb0b6cd4bb2b08f2560a3e564a5614c59/europe#L2942 https://github.com/eggert/tz/blob/bb203f1bb0b6cd4bb2b08f2560...

WorldMaker 2y ago

https://www.icann.org/en/blogs/details/how-time-zones-are-coordinated-13-03-2023-en https://www.icann.org/en/blogs/details/how-time-zones-are-co... Hopefully the British would be kind enough to email the TZ DB group at the IANA (tz@iana.org) a couple years in advance of the legislation to change the name so that the group can get started on collecting the DST rules for Europe/NewNewYork. Some people and devices will probably stick to Europe/Paris out of habit and/or resistance to the change, so the TZ DB would probably be unlikely to remove it, but they may point references from it to Europe/NewNewYork as the new "canonical" name. Plenty of the DB entries are just pointers to other entries already today, for one instance it was decided that America/City and Europe/City maybe is too conflicted a namespace and we see increasingly more "the canonical name is America/State/City" or "the canonical name is Europe/Country/City".

mikepurvis 2y ago
As a Canadian, I would love for my timezone to be Americas/Toronto or Americas/Canada/Toronto rather than America/Toronto, but that's pretty far down my register of first world problems.
- deleted 2y ago
  [deleted]
- mjevans 2y ago
  How about something like: Sol3/CA/Toronto I'd also like all 50 state capitols (and possibly also their largest city) to exist as E.G. Sol3/US/WA-Olympia and Sol3/US/WA-Seattle (respectively to the above; I don't know Canadian provinces that well) Sol3 is a prefix for the 3rd planet (starting ordinal 1, but anything in the orbit of Sol can be Sol0) in our solar system. It's also nicely short so easy to type out in command lines. Every state _should_ have it's own TZ file, even if it's just an alias. That's a good forward compatible way of allowing the same config to work if future legislative efforts produce or remove timezones. It would also allow E.G. Arizona's non DST timezone to remain correctly configured in some future where the US finally ends the nightmare of DST forever.