为什么使用ParseInLocation打印不同的时区？

Question

I'm trying to parse a string into time with a user-specific timezone location -

// error handling skipped for brevity
loc, _ := time.LoadLocation("Asia/Kolkata")
now, _ := time.ParseInLocation("15:04", "10:10", loc)
fmt.Println("Location : ", loc, " Time : ", now)

The output I get on my system is - Location : Asia/Kolkata Time : 0000-01-01 10:10:00 +0553 HMT

Where did this HMT time zone come from?

If instead of parsing the time I use now := time.Now().In(loc), the timezone printed is correct - IST. Am I doing something wrong with timezone parsng or is my system timezone database faulty?

Answer 1

This may be a relic of the fact that your year for now is 0000, while time.Now() returns the current time. Timezones are weird, and certain locations haven't always used the same timezone. This is an excerpt from the IANA Time Zone Database:

# Zone  NAME        GMTOFF  RULES   FORMAT  [UNTIL]
Zone    Asia/Kolkata    5:53:28 -   LMT 1854 Jun 28 # Kolkata
        5:53:20 -   HMT 1870        # Howrah Mean Time?
        5:21:10 -   MMT 1906 Jan  1 # Madras local time
        5:30    -   IST 1941 Oct
        5:30    1:00    +0630   1942 May 15
        5:30    -   IST 1942 Sep
        5:30    1:00    +0630   1945 Oct 15
        5:30    -   IST

If I am interpreting this correctly, it seems HMT was used from 1854 until 1870—I'm not exactly sure why this would cause it to be used for year 0000, which would seem to fall under LMT, but it's possible the Go database is slightly different (or it's possible that I'm misinterpreting the database). If you're concerned about the correct timezone being used for historical dates (like 0000) I'm not sure I can give a great answer, however for anything recent IST should be correctly used.