DateTimeFormatter.ofPattern('zzz') does not include daylight/standard time indicator

[mlc]

On the JDK, the java.time.formatters for the pattern "zzz" return either EDT or EST if you are in America/New York:

However, js-joda returns just ET, omitting the D or S indicator:

I would expect js-joda to be consistent with the JDK and with its own docs, and return EDT here.

[pithu]

Hi @mlc

Thanks for reporting. It might be a bug or missing functionality, i can reproduce the issue for European timezones as well. Looks like the locale formatter is not aware of daylight savings.

const { LocalDateTime, ZoneId, DateTimeFormatter } = require("@js-joda/core");
require("@js-joda/timezone");
const { Locale } = require("@js-joda/locale_de-de");

const f = DateTimeFormatter.ofPattern("h:ma zzz").withLocale(Locale.GERMAN);
const d = LocalDateTime.parse("2021-06-30T08:06:00").atZone(ZoneId.of("Europe/Berlin"));

f.format(d); 
// -> 8:6AM MEZ
// should be -> 8:6AM MESZ

@phueper any ideas ?

[phueper]

Hi,

i don't have an idea... i suppose it is related to locale ... i will try to debug it

[pithu]

After diving into the locale packages, i figured out that this functionality is simply not yet implemented.
So it would be great if someone could improve on this. Its mainly about fixing the printer parser in the locale package -> https://js-joda.github.io/js-joda/file/packages/locale/src/format/cldr/CldrZoneTextPrinterParser.js.html

[phueper]

@pithu i looked a little bit into this ... i believe the problem here is missing support for ZoneRules.isDaylightSavings(),
see this TODO comment https://github.com/js-joda/js-joda/blob/master/packages/locale/src/format/cldr/CldrZoneTextPrinterParser.js#L135
and https://github.com/js-joda/js-joda/blob/master/packages/timezone/src/MomentZoneRules.js#L262

not sure how much effort that would be, i remember, that we talked about this in the past and that it is somehow hard to figure out from the moment data? But i might be wrong here...

[pithu]

Ok, then that would probably mean that we have to fork the moment-timezone grunt tasks and add the daylight saving information to the packed format. I am not sure how much effort that would be, an entry point to understand how its working might be this HowTo i recently added https://github.com/pithu/js-joda/blob/c954cd5991b90ee5e02d4cd92eaddca379de7821/packages/timezone/HowToUpdateTZDB.md

[phueper]

ok ... i'll give it a try ...

[phueper]

fwiw ... some first attempts to get DST info into the timezone packed format are here https://github.com/js-joda/moment-timezone in a clone of moment-timezone

[pithu]

LGTM. What about a PR in js-joda/moment-timezone ?

[phueper]

first step ... PR in js-joda/moment-timezone js-joda/moment-timezone#2