Fix isToday/isTomorrow day diff for UTC dates across timezone and DST boundaries

[paul678]

Summary

This changes _calculateDifference(DateTime date) to preserve the timezone basis of the input date before comparing calendar days.

Previously, the implementation rebuilt both values as local midnights:

DateTime(date.year, date.month, date.day)
DateTime(now.year, now.month, now.day)

That was incorrect when date was UTC, because the UTC date was implicitly converted into a local calendar day before the comparison.

[FMorschel]

Could you please come up with a test case that would fail with the previous implementation and passes now?

Thanks for noticing this!

[paul678]

Could you please come up with a test case that would fail with the previous implementation and passes now?

Thanks for noticing this!

Added a very simple test. It is using the older _calculateDifference implementation with the exact behaivor I observed today which marked 2 days as "today" in my app 😅

I keep UTC dates throughout my app <-> backend communication and was doing a simple serverDate.isToday and 2 of them where showing as true

[FMorschel]

CC @jogboms

For me, the old calculation on the test file is not needed, but since this is a test, I'm not that worried. Since I can't push new versions, anyway, I'll defer to the package owner.

Again, thanks for the PR!

[jogboms]

Really good spot. Thanks @paul678

[jogboms]

Could you investigate the failing test? @paul678

[paul678]

@jogboms Sorry for the delay, got caught in some other stuff...
Seems the tests was failing due to local timezone on CI, trying to force a specific timezone on that one test now and it seems to work 🤞

[codecov]

Codecov Report

❌ Patch coverage is 21.73913% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.36%. Comparing base (421b33a) to head (d0eeef4).

Files with missing lines	Patch %	Lines
test/time_test.dart	14.28%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #80      +/-   ##
==========================================
- Coverage   99.85%   97.36%   -2.50%     
==========================================
  Files           2        2              
  Lines         700      721      +21     
==========================================
+ Hits          699      702       +3     
- Misses          1       19      +18     

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[jogboms]

L5 can be removed, no?