TIL: Sweden had February 30 in 1712 https://en.wikipedia.org/wiki/1712_in_Sweden , so I decided to see how chrono handled that.

use chrono::TimeZone;
use chrono_tz::Europe::Stockholm;

fn main() {
    let feb30 =  Stockholm.ymd(1712,2,30);
    println!("Date: {:?}", feb30);
}

 target/debug/feb30
thread 'main' panicked at /home/snaggen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/chrono-0.4.34/src/offset/mod.rs:252:40:
No such local time
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Result (as expected): Not well! 😄

I also tested Java with

ZonedDateTime feb30 = ZonedDateTime.of(1712,2,30, 0,0,0,0, ZoneId.of("Europe/Stockholm"));

with simmilar result

java.time.DateTimeException: Invalid date 'FEBRUARY 30'

So, lets take a minute of silence for all the programmers of history related software, may the spagetti monster have mercy on their souls.

  • TehPers@beehaw.orgEnglish
    26·
    8 months ago

    I know you’re joking about the bug report, but you could open an issue about it anyway if it genuinely is a thing. I did a quick search though and it looks like it was a transition period between two different calendars. Maybe chrono intentionally assumes Gregorian calendar, or some simplified version of it at least?

    Edit: found this in chrono’s readme:

    Only the proleptic Gregorian calendar (i.e. extended to support older dates) is supported.

    I wouldn’t open an issue actually since this is specifically called out already.

    • snaggen@programming.devOPEnglish
      6·
      8 months ago

      I think there are so much issues with historical dates, that it is probably not worth fixing it in general purpose libraries. Not only do you need to special case everything like this in relation to dates, but you would also need to keep track of all historical territories (like Prussia and such) and what was part of what. In this particular case, I think that the timezone Europe::Helsinki was part of Sweden and should be included (possibly some cities from current Poland). There is no need to add that kind of complexity to general purpose libraries, that should probably be in some special historical date / region library if needed.

      Also, there was not really a concept of time zones before the railway, then the time was floating. The time was not the same in the whole country, because that was not a problem before people started to travel faster and in a way that needed time tables. So, that also fits poorly in a modern general purpose date/time library.

    • sugar_in_your_tea@sh.itjust.works
      8·
      8 months ago

      Even just sticking with UNIX timestamps and relying on a library, dealing with time zones still sucks. Inevitably, your backend and frontend libraries will have some difference in some case that matters for some customer. And it won’t happen just after release, but some months down the road when one country somewhere changes their laws and your libraries don’t get updated in time, or maybe there’s a bug like in the OP.

      Madness lies everywhere when talking about time.

      We should all do ourselves a favor and follow UTC time everywhere. There’s still leap seconds and leap days to deal with, but so many problems just disappear if everyone uses the same time. The sun may come up at 20:00 and go down at 09:00, but your stores can just adjust their hours and it’s totally fine. You won’t ever have to worry about missing a meeting because the organizer’s software and yours got out of sync, and you’ll never have to mentally convert times on a call.

      It’s a small price to pay, but for all our sanity, just use UTC time.

      • robinm@programming.dev
        4·
        8 months ago

        The issue is that the notion of “tomorrow” becomes quite hard to express. If it’s 20:00 when the sun rose, when does tomorrow starts? In 5 hours ?

        • sugar_in_your_tea@sh.itjust.works
          1·
          8 months ago

          No, I think that would still be based on local sun time, and we’d just not use it much when talking to people outside that time zone. So in a video call, we’d just say, “let’s meet at 08:00”, which could be “tomorrow” for some listeners, and could be later today for others. A day would still be from sun-up to sun-down, in colloquial terms, but dates would be from 00:00 to 23:59, so if you wanted to be precise, you’d just say the date.

  • Vorpal@programming.dev
    6·
    8 months ago

    Yes, Sweden really screwed up the first attempt at switching to Gregorian calendar. But there were also multiple countries who switched back and forth a couple of times. Or Switzerland where each administrative region switched separately.

    But I think we in Sweden still “win” for worst screw up. Also, there is no good way to handle these dates without specific reference to precise location and which calender they refer to (timestamps will be ambiguous when switching back to Julian calendar).