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Calender.GetWeekOfYear is not compatible with ISO 8601 and date Unix utility #25762
Description
System.Threading.Thread.CurrentThread.CurrentCulture.Calendar.GetWeekOfYear() return values that are not compatible with ISO 8601 and date Unix utility in some edge cases.
ISO related link
The issue was discovered in PowerShell repo PowerShell/PowerShell#6542 (You should use the build if you want tests with PowerShell Core Get-Date cmdlet).
- See 'First week' in https://en.wikipedia.org/wiki/ISO_week_date#Relation_with_the_Gregorian_calendar
If it is on a Sunday, it is part of week 52 of the previous year.
#'2017-01-01' is 'Sunday, January 1, 2017 12:00:00 AM'
date -d 2017-01-01 +%V #return 52 - right
Get-date 2017-01-01 -UFormat "%V" #return 1 - bug
If 31 December is on a Monday, Tuesday or Wednesday, it is in week 01 of the next year.
#'2007-12-31' is 'Monday, December 31, 2007 12:00:00 AM'
date -d 2011-12-31 +%V #return 01 - right
Get-date 2011-12-31 -UFormat "%V" #return 53 - bug
Activity
tarekgh commentedon Apr 4, 2018
Yes, we are not fully compatible with ISO 8601, you may look at the blog https://blogs.msdn.microsoft.com/shawnste/2006/01/24/iso-8601-week-of-year-format-in-microsoft-net/ for more info which also suggests how you can get the compatible ISO 8601 behavior.
If you want the framework support ISO 8601, please feel free to open new API proposal issue for that. Thanks for reporting the issue.
iSazonov commentedon Apr 9, 2018
@tarekgh Thank for great link!
Issue for API proposal dotnet/corefx#28933