Re: [tz] Extra transition for Europe/London with 2023d

On 2024-01-13 08:58, Brooks Harris wrote:

That's a question I have. As far as I can tell zic creates only one transition per day. There are examples in the source files where the STDOFF changes at YMD 00:00:00 and there is also a DST shift at YMD 02:00:00. That's two transitions in that day. But zic outputs a single transition at YMD 00:00:00. While the formats could presumably handle two transitions per day it appears zic combines them.

What is the TzDb policy here? Paul?

zic coalesces two transitions into one if they occur at the same time. But it shouldn't coalesce a transition with another one that occurs two hours later. If it does that, it's a bug in zic (and probably also a bug in the data).