[Rd] proposal for use ICU for timezone convertion on windows and a draft patch

[yu gong]

Dear All,

 Last week I found an issue about R Sys.timezone function on Windows and send email to this list. This week , I read quite a few  docs and codes about windows time zone to IANA time zone conversion. and found in unicode.org's  ICU library has a function  ucal_getTimeZoneIDForWindowsID which do the time zone convert. Microsoft also use it for time zone convertion in dotnet 6 and 7.(https://github.com/dotnet/runtime/blob/main/src/native/libs/System.Globalization.Native/pal_timeZoneInfo.c) .

IMHO, use this function to implement time zone convert on windows is better than R's hand-write conversion implementation, use the ICU , it will update the conversion when unicode org upgrade the ICU library and no more hand-write conversion code needed. Also RTools already included the ICU library,and R on windows build link ICU lib on default  , so no additional library or tools need for use this function for time zone conversion.

so I wrote a quick and dirty patch use the ucal_getTimeZoneIDForWindowsID, I think maybe better discuss here before I send patch to bugs.r-project.org.
I put the patch on https://github.com/armgong/misc-r-patch/blob/main/registryTZ-ICU.diff.

this patch mainly do following three steps : 1 read current English time zone name from registry ; 2 read current region name from registry(this also affect conversion); 3 use ucal_getTimeZoneIDForWindowsID implement the conversion.

please feel free to share your thoughts or feedbacks of this patch.  if it doable ,then I will modify it and send it to bugs.r-project.org

best regards,
Yu Gong




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