[tz] Irish Standard Time vs Irish Summer Time

Jon Skeet skeet at pobox.com
Fri Jan 19 17:24:36 UTC 2018

I've been trying to work out when and how to chime in, but I think
Stephen's post is closest to my view.

As far as I can tell, Noda Time will technically work.
ZonedDateTime.IsDaylightSavingTime() method will return true for the winter
and false for the summer (from whenever this takes effect, of course - I
haven't checked). That will surprise developers who aren't aware of this
change, and won't surprise developers who *are* aware of this change. I
don't think I know a better solution though.

At a very, very simplistic level, I'd say it's worth weighing up the pros
and cons:

Option 1: Keep the change
- "Technically correct" (maybe - I'll assume it is for the sake of this
- Doesn't revert anything

- Breaks a lot of code right now

Option 2: Defer the change
- Existing software keeps working as expected by most users and developers

- "Technical correctness" is delayed
- Anything which was changed to support 2018a with a bad Irish-specific fix
may get confused again
- We'll never really know when it's safe to apply the change

Option 3: Revert the change forever, possibly formalizing this
- Existing software keeps working as expected by most users and developers

- At odds with technical correctness

For me the "keeping working as expected by most users and developers" is
the most important part... even if developers fix software to "work" and
display things according to Irish legislation, my guess is that it will
confuse a lot of *real users*.

Basically, I value "practical correctness" much, much, much higher than
"technical correctness" here - I would far prefer the Irish legislation to
change in order to get technical correctness...


On 19 January 2018 at 08:44, Stephen Colebourne <scolebourne at joda.org>

> Thanks for the revert, however I disagree that it is an appropriate
> change to make in general.
> The IANA charter of TZDB says:
> "To be clear, the TZ Coordinator SHALL NOT set time zone policy for a
> region but use judgment and whatever available sources exist to assess
> what the average person on street would think the time actually is, or
> in case of historical corrections, was."
> https://tools.ietf.org/html/rfc6557
> I do not believe that the "average man on the street" in Ireland
> thinks their clocks go back in winter, I think they believe their
> clocks go forward in summer. More specifically, the project is about
> de facto time as perceived by the masses, not what the legal documents
> say.
> Stephen
> On 19 January 2018 at 08:14, Paul Eggert <eggert at cs.ucla.edu> wrote:
> > Philip Paeps wrote:
> >>
> >> Given the number of things this break, I would suggest backing the
> change
> >> out for now but pointing out in NEWS that it will come back say one year
> >> from now.
> >>
> >> Replace the actual change by a comment that the current data is
> inaccurate
> >> pending software being fixed.
> >
> >
> > Thanks, this sounds like a good way to go. Proposed patch attached, and
> > installed into the development version on GitHub. Presumably there
> should be
> > a 2018c release quite soon, to get this temporary workaround out the
> door.
> > (2018b has been prepared and published but not announced, since the
> problems
> > with ICU and OpenJDK became apparent during the post-publication
> process.)
> >
> > There is a conflict between the goals of "let's not break anything" and
> > "let's match civil timekeeping practice". I lean towards doing the
> latter as
> > long as it doesn't cause too much trouble for the former. Here it seems
> like
> > there is some trouble with ICU and OpenJDK, so delay seems advisable
> until
> > fixes can be prepared. That being said, I don't want to wait indefinitely
> > for these fixes. This is not a tzdb-specific issue, since POSIX requires
> > support for negative DST (e.g., TZ='IST-1GMT0,M10.5.0,M3.5.0/1' for
> current
> > Irish rules), which means that applications that reject negative DST are
> not
> > portable to standard platforms configured for Irish time.
> >
> > The proposed patch continues to use the "IST is standard time" approach
> for
> > Irish timestamps between October 1968 and October 1971, but I assume
> that's
> > OK since that's what we did before.
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