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Created attachment 21215 [details]
Program demonstrating the problem
The America/Boa_Vista time zone was "interesting" in 2000. The following are the transitions in the year 2000 (and there have been none since) as per http://nodatime.org/tzvalidate/generate:
2000-02-27 03:00:00Z -04:00:00 standard -04
2000-10-08 04:00:00Z -03:00:00 daylight -03
2000-10-15 03:00:00Z -04:00:00 standard -04
The attached program lists:
- The TimeZoneInfo adjustment rules
- All the changes within the year 2000
- The offset at each hour of the UTC day 2000-10-08
Running using netcoreapp1.1 with the .NET Core SDK 1.0.1, we can't see the adjustment rules, but the dates are as expected. (The code always shows January 1st 2000, so we can see where we're starting)
Changes during 2000 (midnight UTC with a different offset from before
Likewise October 8th shows the appropriate transition:
Running using Mono, we get very different results:
... and no transition at all on October 8th.
The adjustment rules look correct to me - the last two are:
[1999-07-01 - 2000-0630]; Delta: 01:00:00
DST start: Month: 10; Week: 1; Day: 3; DoW: Sunday; Time: 00:00; Fixed? True
DST end: Month: 2; Week: 1; Day: 27; DoW: Sunday; Time: 00:00; Fixed? True
[2000-07-01 - 2000-1231]; Delta: 01:00:00
DST start: Month: 10; Week: 1; Day: 8; DoW: Sunday; Time: 00:00; Fixed? True
DST end: Month: 10; Week: 1; Day: 15; DoW: Sunday; Time: 00:00; Fixed? True
Does Mono ignore the final rule, as it's already got a rule that goes up to June 30th?
Side note: in this case, recreating the time zone from its own rules *doesn't* affect the behaviour, unlike in bug 54480.