[tz] Request RE: academic research question re: TZ database

[Scott Kilpatrick]

Hi Andrew,

Regarding the software problem you're seeing, it's quite possibly a result
of using a language or API in which dates -- like 2020-01-09 -- are
represented as localized datetimes at midnight -- like 2020-01-09 at 00:00
in America/Regina. This is a pervasive class of bugs that affects
JavaScript programs for users in Brazil and Chile in particular. JavaScript
because the language's builtin Date representation is a datetime (and the
ubiquitous moment library isn't so careful with it), and Brazilian and
Chilean users because until recently their time zones had midnight spring
forwards. Here's a particularly illuminating example of this class of bugs:
https://github.com/airbnb/react-dates/issues/776.

Hope that helps you track down your software issue.

Scott Kilpatrick
https://typesandtimes.net <http://typesandtimes.net>

On Wed, Jan 8, 2020 at 8:07 PM Paul Eggert <eggert at cs.ucla.edu> wrote:

> On 1/8/20 11:49 AM, Andrew Lyon wrote:
> > It appears that many use the tz database as a source of truth.
>
> Ouch. As we say in big letters, "The tz code and data are by no means
> authoritative." <https://data.iana.org/time-zones/tz-link.html#changes>
>
> > I understand there were 10 years between 1930 and 1941 when the hour of
> > Spring daylight saving transition was 0000 (midnight)  to 0100.  I would
> > like to confirm these entries are in the tz database.
>
> Yes, tzdb says the 10 years 1930/1934 and 1937/1941 all did that, as can
> be seen from the extract Brian emailed.
>
> > I have numerous
> > references that daylight saving time was also observed in
> > America/Regina  during world war ONE ( 1914-1918) and I am uncertain if
> > those entries are in the tz database or the hour of those transitions.
>
> As Brian mentioned, tzdb has these two transitions for 1918:
>
> Sun Apr 14 08:59:59 1918 UT = Sun Apr 14 01:59:59 1918 MST
> Sun Apr 14 09:00:00 1918 UT = Sun Apr 14 03:00:00 1918 MDT
>
> Sun Oct 27 07:59:59 1918 UT = Sun Oct 27 01:59:59 1918 MDT
> Sun Oct 27 08:00:00 1918 UT = Sun Oct 27 01:00:00 1918 MST
>
> However, there's a good chance these data entries are incomplete for
> Regina. It's also possible that the entries for 1930/1941 are wrong. For
> details, please read the commentary for Regina in the northamerica file.
> Here's the current development version:
>
> https://github.com/eggert/tz/blob/master/northamerica
>
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