bug#54764: encode-time: make DST and TIMEZONE fields of the list argument optional ones

[Max Nikulin <manikulin@gmail.com>]

On 01/05/2022 09:32, Paul Eggert wrote:
> On 4/30/22 04:22, Max Nikulin wrote:
>>
>> I posted a corrected version of my `org-encode-time' macro, but I did 
>> not add you to Cc (I sent reply through news.gmane.io), and it has no 
>> special case to check whether `encode-time' supports 6 elements list 
>> argument:

> As I understand it, org-encode-time is intended to be a compatibility 
> function like org-newline-and-indent and org-string-distance. Those are 
> in org-compat.el, so I assumed org-encode-time would be there too.

Maybe you are right. I believe that it should do a bit more than just 
ensure compatibility. An additional goal is to avoid pitfall with list 
vs. separate arguments result discrepancy:

(format-time-string
  "%F %T %z %Z"
  (encode-time 0 30 23 31 3 2022 nil nil "Europe/Madrid")
  "Europe/Madrid")
"2022-03-31 23:30:00 +0200 CEST"

(format-time-string
  "%F %T %z %Z"
  (encode-time '(0 30 23 31 3 2022 nil nil "Europe/Madrid"))
  "Europe/Madrid")
"2022-04-01 00:30:00 +0200 CEST"

> Also, if the intent is to emulate Emacs 29 encode-time, can't we do 
> something like the attached instead? The idea is to implement Emacs 29 
> encode-time both on pre-29 Emacs (that don't support lists of length 6) 
> and post-29 Emacs (which might drop support for the obsolescent form).

> +(if (ignore-errors (encode-time '(0 0 0 1 1 1971)))
> +    (if (ignore-errors (encode-time 0 0 0 1 1 1971))
> +        (defalias 'org-encode-time #'encode-time)
> +      (defun org-encode-time (time &rest args)
> +        (encode-time (if args (cons time args) time))))
> +  (defun org-encode-time (time &rest args)
> +    (if args
> +        (apply #'encode-time time args)
> +      (apply #'encode-time time))))

1. I would prefer macro since it works at compile or load time, so 
runtime impact is minimal.
2. Your variant may be fixed, but currently I do not like behavior for 
Emacs-27. Compare encode-time and org-encode-time with new calling style:

(format-time-string
  "%F %T %z %Z"
  (encode-time '(0 30 23 31 3 2022 nil nil "Europe/Madrid"))
  "Europe/Madrid")
"2022-04-01 00:30:00 +0200 CEST"

(format-time-string
  "%F %T %z %Z"
  (org-encode-time '(0 30 23 31 3 2022 nil nil "Europe/Madrid"))
  "Europe/Madrid")
"2022-03-31 23:30:00 +0200 CEST"