[tz] Java & Rearguard

Steve Summit scs at eskimo.com
Sat Jun 8 00:32:25 UTC 2019

Paul wrote:
> It's not unreasonable to use standard time in POSIX to represent 
> standard time in Ireland.

Indeed.  But I don't think it's as obviously reasonable to be
setting isdst for GMT in winter.

> On 6/6/19 2:25 AM, Stephen Colebourne wrote:
>> Java has never provided accurate time zone names for historic times.
>> I doubt any system does
> Quite true, in large part because accurate time zone names do not exist 
> for most historic times. That being said, there's no doubt that for 
> Ireland in 1970, tzdb gets it right whereas Java gets it wrong.

I'm not sure that's an entirely fair challenge, though.
Given that (as I understand it) Java and ICU/CLDR use tt_isdst
to decide whether to display their equivalents of "GMT" or "IST",
I don't think they *can* get the right answer near 1970, because
tzdb changed its mind about the mapping at that point.

Now, it's true, isdst might not be the best key to use for this
sort of thing any more.  Do we have recommendations for what
projects like Java and ICU/CLDR ought to be keying off of,
if not isdst? (I suppose tt_abbrind, or more likely the actual
string it indexes, might be better.)

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