[tz] OpenJDK/CLDR/ICU/Joda issues with Ireland change

Paul Eggert eggert at cs.ucla.edu
Thu Jan 25 02:09:43 UTC 2018

On 01/24/2018 05:28 PM, Yoshito Umaoka wrote:
> CLDR sets an assumption that name of zones are very stable. For example,
> "Pacific Standard Time" represents standard time used on US Pacific coast
> and the name itself does not change time to time.

Could you clarify how CLDR currently works for Ireland, without the 
proposed tzdb changes? tzdb's current data (which is the same as what it 
was in 2017c) has three types of Irish timestamps that use the 
abbreviation "IST". The first type is for UT+00:34:39 and was observed 
in summer 1916; it has tm_isdst=1. The second type is for UT+01 and was 
observed in summers from 1922 through late 1940, then continuously until 
late 1948, then in summers through 1968, and then in summers from 1972 
through today; it also has tm_isdst=1. The third kind is also for UT+01 
and was observed from late 1968 through late 1971; it has tm_isdst=0.

Are all three types of IST called "Irish Standard Time" in CLDR now? If 
not, then what does CLDR call them and how is this determined? And if 
so, we have a problem since the correct full name for IST is "Irish 
Summer Time" for timestamps before late 1968, and is "Irish Standard 
Time" for timestamps thereafter, and there's nothing in the tzdb data 
proper that specifies the transition date between the two full names.

CLDR is not cast in stone: CLDR called IST "Irish Summer Time" until 
CLDR 26 came out in 2014 - this fixed a bug with post-1968 timestamps at 
the cost of introducing a bug for pre-1968 timestamps. I'm hoping that 
there is some way that we can fix this problem, a problem that exists 
regardless of whether negative DST offsets are used. Perhaps CLDR could 
be extended somehow, so that its reports the proper full names for time 
zones even if that info is not always deducible from the tzdb data proper.

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