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@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: