Subject: bug#78678: closed (Re: bug#78678: [PATCH v2] world-clock: Add user option to control order of entries)

From: [email-masked] (GNU bug Tracking System)
Date: Sat, 14 Jun 2025 14:23:09 +0000

Your bug report

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

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
78678: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=78678
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#78678: [PATCH v2] world-clock: Add user option to control order of entries
From: Eli Zaretskii <[email-masked]>
To: "Jacob S. Gordon" <[email-masked]>
Cc: [email-masked]
Date: Sat, 14 Jun 2025 17:22:29 +0300
List-Id: <debbugs-submit.debbugs.gnu.org>

> Date: Sun, 8 Jun 2025 23:54:06 -0400
> From: "Jacob S. Gordon" <[email-masked]>
> Cc: [email-masked]
> 
> 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?).

Thanks, installed on master, and closing the bug.

(the code as submitted triggered a byte-compiler warning, so I fixed
that by a followup patch.)

Subject: [PATCH v1] world-clock: Sort entries based on a user-provided function
From: "Jacob S. Gordon" <[email-masked]>
To: [email-masked]
Date: Tue, 03 Jun 2025 02:30:59 -0400
List-Id: <debbugs-submit.debbugs.gnu.org>

Tags: patch

Hello all,

Please find below a feature proposal for sorting entries of
world-clock, and a first draft of a patch attached to this message.

# Motivation

The `world-clock' displays time zone entries in the order they appear
in `world-clock-list'. Usually this is enough, since orders like time
can often be done statically. However, there are scenarios where you
might want a dynamic ordering. For example:

1. You work with people in multiple time zones, and you want entries
to appear in order of proximity to working hours, e.g. in what time
zones are people likely to be responsive right now?

2. Daylight savings can go into effect at [different times]. For
example, eastern Europe and Egypt both shift from UTC+2 in the winter
to UTC+3 in the summer.

| Zone           | DST start            | DST end                  |
|----------------+----------------------+--------------------------|
| eastern Europe | last Sunday of March | last Sunday of October   |
| Egypt          | last Friday of April | last Thursday of October |

For a period in the spring, local time in Egypt (UTC+2) is earlier
than eastern Europe (UTC+3). Depending on the year, DST in Egypt may
end earlier or later than in eastern Europe.

In years like 2025 & 2026 where the last Thursday of October is after
the last Sunday of October, there’s no static ordering of the zones
that works all year (bracket contents are UTC offsets at a vertical
time slice):

#+begin_src text
time             |< ~April             ~November >|
Egypt  ---(+2)-----(+2)-|-(+3)--------(+3)---(+3)-|-(+2)-----
Europe ---(+2)---|-(+3)---(+3)--------(+3)-|-(+2)---(+2)-----
#+end_src

In other years like 2027, a consistent ordering is possible:

#+begin_src text
time             |< ~April             ~November >|
Egypt  ---(+2)-----(+2)-|-(+3)--------(+3)-|-(+2)---(+2)-----
Europe ---(+2)---|-(+3)---(+3)--------(+3)---(+3)-|-(+2)-----
#+end_src

[different times]
https://en.wikipedia.org/wiki/Daylight_saving_time_by_country

# Possible Implementation

A simple way to do this is with a `world-clock-sort-function' custom
variable that sorts the entries in `world-clock-display'.

#+begin_src emacs-lisp
(setopt world-clock-sort-function 'my/world-clock-sort-function)
#+end_src

You could then accomplish each of the orderings mentioned earlier:

1. Time zones appear in order of how far they are from the middle of
the workday:

#+begin_src emacs-lisp
(defun my/world-clock-sort-function (tzlist)
  "Sort on proximity of local time to work hours."
  (let* ((now (current-time))
         (start 9)
         (end  17)
         (mid (/ (+ start end) 2.0)))
    (sort tzlist
          :key (lambda (entry)
                 (pcase-let* ((zone (car entry))
                              (`(,s ,m ,h _) (decode-time now zone))
                              (hour (+ h (/ m 60.0) (/ s 3600.0)))
                              (diff (min (abs (- hour (- mid 24)))
                                         (abs (- hour mid))
                                         (abs (- hour (+ mid 24))))))
                   diff)))))
#+end_src

2. Sort on an ISO-8601 timestamp so zones are always in ascending
order:

#+begin_src emacs-lisp
(defun my/world-clock-sort-function (tzlist)
  "Sort on local ISO-8601 timestamps."
  (let ((now (current-time)))
    (sort tzlist
          :key (lambda (entry)
                 (let ((zone (car entry)))
                   (format-time-string "%FT%T" now zone))))))
#+end_src

Note that in the current patch there’s a small race condition between
recording the current time in `world-clock-display' and sorting the
list.

Any thoughts on this idea and the interface?

Thanks,

-- 
Jacob S. Gordon
[email-masked]

=========================

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In GNU Emacs 30.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.49,
cairo version 1.18.4)
System Description: Arch Linux

Configured using:
 'configure --with-pgtk --sysconfdir=/etc --prefix=/usr
 --libexecdir=/usr/lib --localstatedir=/var --disable-build-details
 --with-cairo --with-harfbuzz --with-libsystemd --with-modules
 --with-native-compilation=aot --with-tree-sitter 'CFLAGS=-march=x86-64
 -mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=3
 -Wformat -Werror=format-security -fstack-clash-protection
 -fcf-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g
 -ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto'
 'LDFLAGS=-Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro
 -Wl,-z,now -Wl,-z,pack-relative-relocs -flto=auto'
 'CXXFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions
 -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security
 -fstack-clash-protection -fcf-protection -fno-omit-frame-pointer
 -mno-omit-leaf-frame-pointer -Wp,-D_GLIBCXX_ASSERTIONS -g
 -ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto''

>From 0d293d92d81d1086a63942734fa067c4f0ca0bfe Mon Sep 17 00:00:00 2001
From: "Jacob S. Gordon" <[email-masked]>
Date: Mon, 2 Jun 2025 21:06:37 -0400
Subject: [PATCH v1] world-clock: Sort entries based on a user-provided
 function

The 'world-clock' displays time zone entries in the order they appear in
'world-clock-list' (or a default if unset).  We introduce a custom
variable 'world-clock-sort-function' to generate an order on each update
of 'world-clock-display'.  The default value of 'identity' preserves the
existing behavior.

* lisp/time.el (world-clock-sort-function, world-clock-display):

Add custom variable 'world-clock-sort-function', and sort time zone
entries in 'world-clock-display' according to it.
---
 etc/NEWS     | 10 ++++++++++
 lisp/time.el | 15 +++++++++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 01ed372a2da..001609c5b21 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2120,6 +2120,16 @@ You can now use the mouse wheel to scroll the calendar by 3 months.
 With the shift modifier, it scrolls by one month.  With the meta
 modifier, it scrolls by year.
 
+
+** Time
+
+*** New user option 'world-clock-sort-function'
+
+The order of time zone entries in the 'world-clock' is updated according
+to the 'world-clock-sort-function'.  By default, no sorting is done and
+entries appear according to their order in 'world-clock-list' (or a
+default if unset).
+
 * New Modes and Packages in Emacs 31.1
 
 ** New minor mode 'delete-trailing-whitespace-mode'.
diff --git a/lisp/time.el b/lisp/time.el
index fd66775c879..2456ff279e4 100644
--- a/lisp/time.el
+++ b/lisp/time.el
@@ -536,6 +536,15 @@ world-clock-timer-second
   :type 'natnum
   :version "28.1")
 
+(defcustom world-clock-sort-function 'identity
+  "Function to sort time zone entries upon each `world-clock-display'.
+It should take a list of `(TIMEZONE LABEL)' entries and return the same.
+
+This function will be called with `world-clock-list' if set, otherwise
+with a default."
+  :version "31.1"
+  :type '(function :tag "Sorting function"))
+
 (defface world-clock-label
   '((t :inherit font-lock-variable-name-face))
   "Face for time zone label in `world-clock' buffer.")
@@ -563,14 +572,16 @@ world-clock--timer
   "The current world clock timer.")
 
 (defun world-clock-display (alist)
-  "Replace current buffer text with times in various zones, based on ALIST."
+  "Replace current buffer text with times in various zones, based on ALIST.
+The displayed entries are sorted according to `world-clock-sort-function'."
   (let ((inhibit-read-only t)
 	(buffer-undo-list t)
 	(now (current-time))
+	(sorted-zones (funcall world-clock-sort-function alist))
 	(max-width 0)
 	result fmt)
     (erase-buffer)
-    (dolist (zone alist)
+    (dolist (zone sorted-zones)
       (let* ((label (cadr zone))
 	     (width (string-width label)))
 	(push (cons label

base-commit: 50e3bce315eb499917c1d208f87f84315f1a8b4e
-- 
Jacob S. Gordon
[email-masked]

=========================

Please avoid sending me HTML emails and MS Office documents.
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