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

Michael H Deckers michael.h.deckers at googlemail.com
Sun Jan 28 19:00:06 UTC 2018

On 2018-01-26 22:16, Paul Eggert wrote about the tzdb dst bit:
> On 01/26/2018 01:39 PM, Michael H Deckers via tz wrote:
>> Before this change proceeds, it is, in my opinion, necessary
>>     to obtain agreement on what the new significant (non-vestigial)
>>     role of the dst bit, if any, should be in the future (beyond the
>>     single case of Ireland).
> I don't think there's much disagreement over what the bit means in the 
> context of the POSIX API. For example, POSIX specifies that this 
> environment setting:
> TZ='IST-1GMT0,M10.5.0,M3.5.0/1'
> means that standard time is abbreviated "IST" and is 1 hour ahead of 
> UTC, that daylight saving time is abbreviated "GMT" and is at UTC, and 
> that the European Union's current rules are in place for when to 
> change UTC offsets. tzcode and every other POSIX-compatible system 
> support this, and set tm_isdst=1 in winter with a negative DST offset 
> when operating in this locale. As far as I know there's no serious 
> dispute about this, nor is anybody seriously proposing to change this 
> behavior. That is, the tm_isdst API may be vestigial, but it's too 
> late to change what it means.
    No, no: POSIX does not say anything about the setting of the 
tm_isdst member for a given TZ string;
    nor does it talk which part of the TZ string describes daylight 
saving time. I am reluctant to accept
    any assertion of the type it is clear that POSIX means XXX without a 
specific reference implying it;
    if I have to write reliable code, I have to know exactly what I can 
rely on.

    Michael Deckers.

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