-UFormat "%V" logic incorrect for 2021, counts based off calendar day instead of DOW

Getting the week number starts counting in 7 day increments on 1/1/2021 instead of following ISO standard of starting with Monday (if needed, full details in Wikipedia article and probably other locations).

Note: similar to 11534, closed fixed for 2020. Issue 4750 tracks a bunch of complaints with UFormat but is really old and doesn’t appear focused on a specific item. It’s hard to tell if this issue is being addressed by that item.

Steps to reproduce

(get-date 2020-12-31 -UFormat "%V")
(get-date 2021-01-01 -UFormat "%V")
(get-date 2021-01-08 -UFormat "%V")

Expected behavior

53
53
1

Actual behavior

53
1
2

Environment data

Name                           Value
----                           -----
PSVersion                      6.0.0
PSEdition                      Core
GitCommitId                    v6.0.0
OS                             Linux 3.10.0-693.11.6.el7.x86_64 #1 SMP Thu Jan 4 01:06:37 UTC 2018
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[ReevesL]

Got it, thanks. I saw that this was for PowerShell 6 and 7 issues. I see it’s fixed in 7 but not in 6. I’ll assume fixing 6 is no longer in play and close this. I’ll upgrade my Linux host from 6 to 7 and be a happy camper.

Thanks brianary & iSazonov.

[brianary]

While Windows PowerShell (powershell.exe) 5.1 (and earlier) erroneously returns 2 for Get-Date 2021-01-08 -UFormat %V, PowerShell Core (pwsh.exe) 7.1 (this project) returns 01.

It looks like the old PowerShell is just calculating %V as [Math]::Floor($_.DayOfYear/7)+1, but I’m not sure where to report that.