From 3c728d4c69f2abe991ef84787ae1014ad1cd29d2 Mon Sep 17 00:00:00 2001
From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Sun, 9 Aug 2020 12:34:23 +0200
Subject: [PATCH] Add a variable to allow displaying numeric time zones

* lisp/calendar/calendar.el (calendar-use-numeric-time-zones): New
variable.

* doc/emacs/calendar.texi (Sunrise/Sunset): Document it (bug#33149).

* lisp/calendar/cal-dst.el (calendar-standard-time-zone-name): Use it.
(calendar-daylight-time-zone-name): Ditto.

* lisp/calendar/solar.el (sunrise-sunset): Adjust usage.
(solar-equinoxes-solstices): Ditto.
---
 doc/emacs/calendar.texi   |  5 +++++
 etc/NEWS                  |  7 +++++++
 lisp/calendar/cal-dst.el  | 16 ++++++++++++++--
 lisp/calendar/calendar.el |  7 +++++++
 lisp/calendar/solar.el    |  9 +++++++--
 5 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/doc/emacs/calendar.texi b/doc/emacs/calendar.texi
index fe51ad35d77..31db815df70 100644
--- a/doc/emacs/calendar.texi
+++ b/doc/emacs/calendar.texi
@@ -625,6 +625,11 @@ your time zone.  Emacs displays the times of sunrise and sunset
 @emph{corrected for daylight saving time}.  @xref{Daylight Saving},
 for how daylight saving time is determined.
 
+@vindex calendar-use-numeric-time-zones
+  If you want to display numerical time zones (like @samp{"+0100"})
+instead of symbolic time zones (like @samp{"CET"}), set the
+@code{calendar-use-numeric-time-zones} variable to non-@code{nil}.
+
   As a user, you might find it convenient to set the calendar location
 variables for your usual physical location in your @file{.emacs} file.
 If you are a system administrator, you may want to set these variables
diff --git a/etc/NEWS b/etc/NEWS
index 71c037631af..2f204a5b4bc 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -194,6 +194,13 @@ The presence of a space between an open paren and a symbol now is
 taken as a statement by the programmer that this should be indented
 as a data list rather than as a piece of code.
 
+** Calendar
+
+*** New variable 'calendar-use-numeric-time-zones' to use numeric time zones.
+If non-nil, functions that display time zones (like the 'S' command in
+calendar mode that displays the sunrise time) will display time zones
+like "+0100" instead of "CET".
+
 ** Dired
 
 *** New user option 'dired-mark-region' affects all Dired commands
diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el
index 3db12e668ab..af6acaf09ad 100644
--- a/lisp/calendar/cal-dst.el
+++ b/lisp/calendar/cal-dst.el
@@ -350,17 +350,29 @@ If the locale never uses daylight saving time, set this to 0."
   :group 'calendar-dst)
 
 (defcustom calendar-standard-time-zone-name
-  (or (nth 2 calendar-current-time-zone-cache) "EST")
+  (if calendar-use-numeric-time-zones
+      (if calendar-current-time-zone-cache
+          (format-time-string
+           "%z" 0 (* 60 (car calendar-current-time-zone-cache)))
+        "+0000")
+    (or (nth 2 calendar-current-time-zone-cache) "EST"))
   "Abbreviated name of standard time zone at `calendar-location-name'.
 For example, \"EST\" in New York City, \"PST\" for Los Angeles."
   :type 'string
+  :version "28.1"
   :group 'calendar-dst)
 
 (defcustom calendar-daylight-time-zone-name
-  (or (nth 3 calendar-current-time-zone-cache) "EDT")
+  (if calendar-use-numeric-time-zones
+      (if calendar-current-time-zone-cache
+          (format-time-string
+           "%z" 0 (* 60 (cadr calendar-current-time-zone-cache)))
+        "+0000")
+    (or (nth 3 calendar-current-time-zone-cache) "EDT"))
   "Abbreviated name of daylight saving time zone at `calendar-location-name'.
 For example, \"EDT\" in New York City, \"PDT\" for Los Angeles."
   :type 'string
+  :version "28.1"
   :group 'calendar-dst)
 
 (defcustom calendar-daylight-savings-starts-time
diff --git a/lisp/calendar/calendar.el b/lisp/calendar/calendar.el
index 1d5b9479e2b..9a6c78a50eb 100644
--- a/lisp/calendar/calendar.el
+++ b/lisp/calendar/calendar.el
@@ -1061,6 +1061,13 @@ calendar."
   :type 'boolean
   :group 'holidays)
 
+(defcustom calendar-use-numeric-time-zones nil
+  "If nil, use symbolic time zones like \"CET\" when displaying dates.
+If non-nil, use numeric time zines like \"+0100\"."
+  :type 'boolean
+  :version "28.1"
+  :group 'calendar)
+
 ;;; End of user options.
 
 (calendar-recompute-layout-variables)
diff --git a/lisp/calendar/solar.el b/lisp/calendar/solar.el
index 6a813e9ee82..20a20df4603 100644
--- a/lisp/calendar/solar.el
+++ b/lisp/calendar/solar.el
@@ -840,7 +840,9 @@ This function is suitable for execution in an init file."
                             "E" "W"))))))
          (calendar-standard-time-zone-name
           (if (< arg 16) calendar-standard-time-zone-name
-            (cond ((zerop calendar-time-zone) "UTC")
+            (cond ((zerop calendar-time-zone)
+                   (if calendar-use-numeric-time-zones
+                       "+0100" "UTC"))
                   ((< calendar-time-zone 0)
                    (format "UTC%dmin" calendar-time-zone))
                   (t  (format "UTC+%dmin" calendar-time-zone)))))
@@ -1013,7 +1015,10 @@ Requires floating point."
   (let* ((m displayed-month)
          (y displayed-year)
          (calendar-standard-time-zone-name
-          (if calendar-time-zone calendar-standard-time-zone-name "UTC"))
+          (cond
+           (calendar-time-zone calendar-standard-time-zone-name)
+           (calendar-use-numeric-time-zones "+0100")
+           (t "UTC")))
          (calendar-daylight-savings-starts
           (if calendar-time-zone calendar-daylight-savings-starts))
          (calendar-daylight-savings-ends
-- 
2.39.2