GNU bug report logs - #78678
[PATCH v1] world-clock: Sort entries based on a user-provided function

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From: "Jacob S. Gordon" <jacob.as.gordon <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 78678 <at> debbugs.gnu.org
Subject: bug#78678: [PATCH v2] world-clock: Add user option to control order of entries
Date: Sun, 8 Jun 2025 23:54:06 -0400

[Message part 1 (text/plain, inline)]

Hello,

On 2025-06-03 08:00, Eli Zaretskii wrote:
> This requires users to be Lisp programmers.  If there are
> reasonably-useful cases where a certain order would be desirable,
> allowing users to customize a variable using symbol values makes the
> feature much more friendly to users who are not programmers.  Would
> it make sense to add a couple of such values?

I agree, and I think it does make sense. After trying a version with
symbols for common use-cases, I think the most flexible option is to
allow the user to provide a format for `format-time-string' to act as
the sorting key. This is similar in complexity to the variable
`world-clock-time-format', and some predefined values can be put in
the `:type' block of the `defcustom':

#+begin_src emacs-lisp
:type '(choice (const :tag "No sorting" nil)
               (const :tag "Chronological order" "%FT%T")
               (const :tag "Reverse chronological order" ("%FT%T" . t))
               (const :tag "Time of day order" "%T")
               (const :tag "Reverse time of day order" ("%T" . t))
               (string :tag "Format string")
               (cons :tag "Format string and reverse flag"
                     (string :tag "Format string")
                     (boolean :tag "Reverse"))
               (function :tag "Sorting function")))
#+end_src

Then, sorting can be switched based on the type in a helper function:

#+begin_quote
(defun world-clock--sort-entries (tzlist time)
  "Sort TZLIST according to `world-clock-sort-order' at a given TIME."
  (pcase world-clock-sort-order
    ((pred null) tzlist)
    ((or (and (pred stringp) format)
        `(,(and (pred stringp) format) .
          ,(and (pred booleanp) reverse)))
     (sort tzlist
           :key (lambda (entry)
                   (format-time-string format time (car entry)))
           :reverse reverse))
    ((pred functionp) (funcall world-clock-sort-order tzlist time))
    (_ (error "Invalid `world-clock-sort-order': `%s'"
              world-clock-sort-order))))
#+end_quote

In terms of coding standards:

+ I could do this without `pcase', if desired.
+ I can write unit tests if we’re okay with the idea.

> Please reformat the log message according to our conventions
> (described in CONTRIBUTE).

Done in the updated patch (I think?).

Thank you!

-- 
Jacob S. Gordon
jacob.as.gordon <at> gmail.com

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[v2-0001-world-clock-Add-user-option-to-control-entry-order.patch (text/x-patch, attachment)]

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