Re: tabulated-list sort icon is reversed

[Philippe Vaucher <philippe.vaucher@gmail.com>]

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> Thanks.  See some minor comments below.
>

Thanks for the feekback. Here is a patch with all your suggested
modifications.

About the manual, given it's the first time I edit it I went for a very
minimalist approach, please tell me if I should mention the default values,
or the type of the defcustom in there.

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From 83e9058179405f44f95f493320121313d307d56e Mon Sep 17 00:00:00 2001
From: Philippe Vaucher <philippe.vaucher@gmail.com>
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
* doc/lispref/modes.texi: Add documentation for
  'tabulated-list-gui-sort-indicator-asc',
  'tabulated-list-gui-sort-indicator-desc',
  'tabulated-list-tty-sort-indicator-asc' and
  'tabulated-list-tty-sort-indicator-desc'.
* lisp/emacs-lisp/tabulated-list.el (tabulated-list): New group.
(tabulated-list-gui-sort-indicator-asc)
(tabulated-list-gui-sort-indicator-desc)
(tabulated-list-tty-sort-indicator-asc)
(tabulated-list-tty-sort-indicator-desc): New defcustom.
(tabulated-list-glyphless-char-display): Remove.
(tabulated-list-make-glyphless-char-display-table): New function.
---
 doc/lispref/modes.texi            | 16 ++++++++
 etc/NEWS                          |  9 +++++
 lisp/emacs-lisp/tabulated-list.el | 62 ++++++++++++++++++++++++++-----
 3 files changed, 77 insertions(+), 10 deletions(-)

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index 22592a57b0..d30bd9854e 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -1015,6 +1015,22 @@ list-processes}).  The listing command should create or switch to a
 buffer, turn on the derived mode, specify the tabulated data, and
 finally call @code{tabulated-list-print} to populate the buffer.
 
+@defopt tabulated-list-gui-sort-indicator-asc
+Indicator for column sorted in ascending order, for GUI frames.
+@end defopt
+
+@defopt tabulated-list-gui-sort-indicator-desc
+Indicator for column sorted in descending order, for GUI frames.
+@end defopt
+
+@defopt tabulated-list-tty-sort-indicator-asc
+Indicator for column sorted in ascending order, for text-mode frames.
+@end defopt
+
+@defopt tabulated-list-tty-sort-indicator-desc
+Indicator for column sorted in ascending order, for text-mode frames.
+@end defopt
+
 @defvar tabulated-list-format
 This buffer-local variable specifies the format of the Tabulated List
 data.  Its value should be a vector.  Each element of the vector
diff --git a/etc/NEWS b/etc/NEWS
index 3e347b5318..6119acdf15 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 (see variables
+'tabulated-list-gui-sort-indicator-asc',
+'tabulated-list-gui-sort-indicator-desc',
+'tabulated-list-tty-sort-indicator-asc' and
+'tabulated-list-tty-sort-indicator-desc')
+
 \f
 * Editing Changes in Emacs 27.1
 
diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index 12d0151d67..9021f825b2 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -36,10 +36,45 @@
 
 ;;; Code:
 
+(defgroup tabulated-list nil
+  "Tabulated-list customization group.")
+
+(defcustom tabulated-list-gui-sort-indicator-asc ?▼
+ "Indicator for column sorted in ascending order, for GUI frames. See
+  `tabulated-list-tty-sort-indicator-asc' for indicator used on
+  text-mode frames."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-gui-sort-indicator-desc ?▲
+ "Indicator for column sorted in descending order, for GUI frames. See
+  `tabulated-list-tty-sort-indicator-desc' for indicator used on
+  text-mode frames."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-tty-sort-indicator-asc ?v
+ "Indicator for column sorted in ascending order, for text-mode
+  frames. See `tabulated-list-gui-sort-indicator-asc' for indicator
+  used on GUI frames."
+  :group 'tabulated-list
+  :type 'character
+  :version "27.1")
+
+(defcustom tabulated-list-tty-sort-indicator-desc ?^
+ "Indicator for column sorted in ascending order, for text-mode
+  frames. See `tabulated-list-gui-sort-indicator-asc' for indicator
+  used on GUI frames."
+  :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
-;; still valid.  See, for example, ebuff-menu.el.
+;; still valid. See, for example, ebuff-menu.el.
 
 (defvar-local tabulated-list-format nil
   "The format of the current Tabulated List mode buffer.
@@ -174,14 +209,21 @@ 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 for text-mode frames. This table is used for displaying the
+sorting indicators, see variables
+`tabulated-list-tty-sort-indicator-asc' and
+`tabulated-list-tty-sort-indicator-desc' for more information."
   (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 +273,8 @@ 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 +697,7 @@ 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