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

[Paul Eggert]

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.

The disagreement is not over the role of the tm_isdst bit; it is whether 
tzdb and/or OpenJDK should model Irish Standard Time as a standard time 
(tm_isdst=0) or as a daylight saving time (tm_isdst=1), and similarly 
for any other locales in a similar boat where standard time is ahead of 
the alternative (or "daylight saving") time.