Date: Wed, 5 Jun 2019 11:51:25 +0100 From: Stephen Colebourne <scolebourne@joda.org> Message-ID: <CACzrW9C+bnc0waSbcaVisHG-cJqQ2q8pMTvT1a8aL4uJjC9uwg@mail.gmail.com> | The assumption is that daylight=summer/advanced, and this goes a long | way down the stack, notably into CLDR. What are you planning to do when some jurisdiction does summer/retarted ? And before anyone claims that's absurd, it isn't really. Queensland in AU has never really done summer time (they tried it briefly, once, I think). I suspect that it is a combination of the lifestyle in the areas that really matter (the south east corner) along with that being moderately east in the +1000 time band - that is, they already have natural negative summer time. In summer, which is also monsoon (cyclone) season, it tends to get dark(ish) early (caused as much by thick clouds as sun position) with plenty of rain around - making it daylight later would not help a lot. On the other hand, it also gets light early - and is warm and fine early, so lots of people do (or did when I lived in that area) use the early morning hours for what people in other places tend to do in the evenings (recreationally, going out to eat, movies, etc, doesn't need daylight...) That is, it is commmon for people to wake up around 5 (when the sun has been up for a while) and go fishing, surfing, play a round of golf, or whatever, and after that, go to work - rather than wanting to do any of those things in the evenings when it is less likely to be practical because of the weather. In that environment, moving more sunlight period earlier into the morning (get the dew off the greens, ...) isn't an absurd idea. I doubt it will happen, but who knows? If you are expecting ("assuming") it can never happen, then you could be in for a lot of problems. Note, that the strategy of making the earlier time be "standard" time with tm_isdst 0 in this scenario would have standard time in summer, and winter time (tm_idst === 1) in winter. Nothing like anyone would naturally expect things to be. And of course even that assume that there is just one switch - it would be less needed in mid-summer when it gets light quite early anyway, but of more benefit in spring/autumn - but most likely with different amounts of time shift for each of those periods (I can imagine 30 mins in Spring (October) and an hour in Autumn (March - it fits better). However long you have been making assumptions about how time works, it really is time (!?) to stop, and phase out everything - all that is possible is to convert a UTC timestamp into the local time for the zone, and given a zone offset, convert local time back to a UTC time (the zone offset is needed, a "is xxx" boolean is simply not enough). kre