From f1a316fb834566dae1b76c815af32e51987166cd Mon Sep 17 00:00:00 2001
From: Philippe Vaucher <address@hidden>
Date: Sat, 2 Mar 2019 20:03:41 +0100
Subject: [PATCH] Customize tabulated-list sort indicators

This allows the user to customize the sorting indicators displayed
near the current column.

* etc/NEWS: Mention changes
* lisp/emacs-lisp/tabulated-list.el (tabulated-list): New group.
(tabulated-list-gui-sort-indicator-asc): New defcustom.
(tabulated-list-gui-sort-indicator-desc): New defcustom.
(tabulated-list-tty-sort-indicator-asc): New defcustom.
(tabulated-list-tty-sort-indicator-desc): New defcustom.
(tabulated-list-glyphless-char-display): Removal.
(tabulated-list-make-glyphless-char-display-table): New function.
---
 etc/NEWS                          |  9 ++++++
 lisp/emacs-lisp/tabulated-list.el | 52 +++++++++++++++++++++++++------
 2 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index b265185567..a2cdec0083 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -279,6 +279,15 @@ matches strings where the pattern appears as a subsequence.  Put
 simply, makes "foo" complete to both "barfoo" and "frodo".  Add 'flex'
 to 'completion-styles' or 'completion-category-overrides' to use it.
 
++++
+** New user options for tabulated list sort indicators
+The user can customize which sorting indicator character to display
+near the current column in Tabulated Lists:
+- tabulated-list-gui-sort-indicator-asc
+- tabulated-list-gui-sort-indicator-desc
+- tabulated-list-tty-sort-indicator-asc
+- tabulated-list-tty-sort-indicator-desc
+
 
 * Editing Changes in Emacs 27.1
 
diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index 12d0151d67..cc82d3397d 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -36,6 +36,37 @@
 
 ;;; Code:
 
+(defgroup tabulated-list nil
+  "Tabulated-list customization group.")
+
+(defcustom tabulated-list-gui-sort-indicator-asc ?▼
+  "GUI indicator displayed near the current column when the sort order
+is ascending."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-gui-sort-indicator-desc ?▲
+  "GUI indicator displayed near the current column when the sort order
+is descending."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-tty-sort-indicator-asc ?v
+  "TTY indicator displayed near the current column when the sort order
+is ascending."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-tty-sort-indicator-desc ?^
+  "TTY indicator displayed near the current column when the sort order
+is descending."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
 ;; The reason `tabulated-list-format' and other variables are
 ;; permanent-local is to make it convenient to switch to a different
 ;; major mode, switch back, and have the original Tabulated List data
@@ -174,14 +205,17 @@ If ADVANCE is non-nil, move forward by one line afterwards."
     map)
   "Local keymap for `tabulated-list-mode' sort buttons.")
 
-(defvar tabulated-list-glyphless-char-display
+(defun tabulated-list-make-glyphless-char-display-table ()
+  "Make the `glyphless-char-display' table used in Tabulated List buffers."
   (let ((table (make-char-table 'glyphless-char-display nil)))
     (set-char-table-parent table glyphless-char-display)
-    ;; Some text terminals can't display the Unicode arrows; be safe.
-    (aset table 9650 (cons nil "^"))
-    (aset table 9660 (cons nil "v"))
-    table)
-  "The `glyphless-char-display' table in Tabulated List buffers.")
+    (aset table
+          tabulated-list-gui-sort-indicator-desc
+          (cons nil (char-to-string tabulated-list-tty-sort-indicator-desc)))
+    (aset table
+          tabulated-list-gui-sort-indicator-asc
+          (cons nil (char-to-string tabulated-list-tty-sort-indicator-asc)))
+    table))
 
 (defvar tabulated-list--header-string nil
   "Holds the header if `tabulated-list-use-header-line' is nil.
@@ -231,8 +265,8 @@ Populated by `tabulated-list-init-header'.")
 		  (concat label
 			  (cond
 			   ((> (+ 2 (length label)) width) "")
-			   ((cdr tabulated-list-sort-key) " ▲")
-			   (t " ▼")))
+			   ((cdr tabulated-list-sort-key) (format " %c" tabulated-list-gui-sort-indicator-desc))
+			   (t (format " %c" tabulated-list-gui-sort-indicator-asc))))
 		  'face 'bold
 		  'tabulated-list-column-name label
 		  button-props))
@@ -655,7 +689,7 @@ as the ewoc pretty-printer."
   (setq-local truncate-lines t)
   (setq-local buffer-undo-list t)
   (setq-local revert-buffer-function #'tabulated-list-revert)
-  (setq-local glyphless-char-display tabulated-list-glyphless-char-display)
+  (setq-local glyphless-char-display (tabulated-list-make-glyphless-char-display-table))
   ;; Avoid messing up the entries' display just because the first
   ;; column of the first entry happens to begin with a R2L letter.
   (setq bidi-paragraph-direction 'left-to-right)
-- 
2.17.1