parsing local-time

[knobo]

How can I parse a date at a timezone and get back a timestamp in local-time
The date "2016-12-01" in 'America/Aruba' would be at "2016-12-01T05:00:00+01" in norway.

I can not just use the :offset in parse-timestring because I don't know if it is daylight savings time or not before after the date is parsed.

To explain with an example:
In postgresql I do this:

select  TIMESTAMP '2016-12-01' at time zone 'America/Aruba';
        timezone        
------------------------
 2016-12-01 05:00:00+01

[orivej]

Not sure whether this can be simplified, but it should work:

(apply #'encode-timestamp
       `(,@(subseq (multiple-value-list
                    (decode-timestamp (parse-timestring "2016-12-01")
                                      :timezone +utc-zone+))
                   0 7)
           :timezone ,(find-timezone-by-location-name "America/Aruba")))

(utc here ensures that decode-timestamp returns the original parts of the timestamp, since parse-timesting assumes UTC.)

[orivej]

This is simpler:

(apply #'encode-timestamp
       `(,@(substitute 0 nil (reverse (subseq (split-timestring "2016-12-01") 0 7)))
           :timezone ,(find-timezone-by-location-name "America/Aruba")))

[myrkraverk]

The workaround I came up with, is

(local-time:parse-timestring "2024-09-01" :offset (local-time::subzone-offset (local-time::%subzone-as-of tz nil nil)))

which I'm not sure is much better. It relies on private interfaces.

But now the round trip (parse-timestring ...) to (format-timeststring ... :timezone tz) for date inputs of the form YYYY-MM-DD is consistent.

I did not know about this issue, nor pull request #58 before discovering that; I haven't looked into the details of what it does.