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Re: [O] Bug: org-2ft and/or float-time is wrong [9.1.2 (9.1.2-22-ga2a034

From: Allen Li
Subject: Re: [O] Bug: org-2ft and/or float-time is wrong [9.1.2 (9.1.2-22-ga2a034-elpaplus @ ~/.emacs.d/elpa/org-plus-contrib-20171023/)]
Date: Mon, 30 Oct 2017 21:33:37 -0700

On Mon, Oct 30, 2017 at 5:40 PM, Allen Li <address@hidden> wrote:
> (current-time-string (time-to-seconds (org-2ft "<2017-10-31>")))
> "Sun Oct 29 17:00:00 2017"
> This seems wrong
> In org-2ft
> (org-parse-time-string s nil t)
> The t means use UTC instead of Emacs local time.
> However, Org translates <now> into (float-time), which is in Emacs localtime.
> 1. SCHEDULED>"<now>" compares a UTC time against a local time.
> 2. Either org-2ft should be fixed to be localtime, or <now> should be
> (float-time) in UTC.
> I don't know how Org internals works, but my experience so far has
> been that Emacs and *nix in general is very naive about timezones; a
> naked timestamp is assumed to be localtime if it does not have
> accompanying timezone information.
> Thus, it seems to be more correct to change org-2ft to parse times as
> localtime.  However, I don't know if UTC timestamps are assumed by
> other parts of Org internals, in which case fixing <now> (float-time)
> would be safest.

My initial analysis was wrong because I wasn't thinking clearly.

Just to set a stake in the ground: timestamps are seconds since epoch
and timezone neutral.  Emacs time values are also timezone neutral:
(sec-high sec-low microsec picosec)

(current-time-string (float-time))
"Mon Oct 30 21:21:31 2017" ; right

(current-time-string (org-time-today))
"Mon Oct 30 00:00:00 2017" ; right

(current-time-string (org-2ft "<2017-10-31>"))
"Mon Oct 30 17:00:00 2017" ; wrong

Removing the t for zone fixes it

(defun org-2ft (s)
  "Convert S to a floating point time.
If S is already a number, just return it.  If it is a string, parse
it as a time string and apply `float-time' to it.  If S is nil, just return 0."
   ((numberp s) s)
   ((stringp s)
    (condition-case nil
(float-time (apply #'encode-time (org-parse-time-string s)))
      (error 0.)))
   (t 0.)))

(current-time-string (org-2ft "<2017-10-31>"))
"Tue Oct 31 00:00:00 2017" ; now right

I will also note that the FIXME comment in org-parse-time-string
suggests that it too is not handling timezones correctly.  In fact,
perhaps org-parse-time-string should not take a zone argument, since
Org does not support timezones thus the only valid value for zone is
nil.  I suspect that org-display-custom-time, another caller that
passes t for zone, is also timezone incorrect.

That is to say, nothing in Org allows passing in a custom timezone,
let alone a UTC timezone; thus, every caller that passes a non-nil
zone to org-parse-time-string is getting an incorrect result.

tl;dr time is hard.

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