master 6a60bd4 2/2: Add a new minor mode `glyphless-display-mode'

[Lars Ingebrigtsen]

branch: master
commit 6a60bd475d67b7e8c9184836abf7eea229183066
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Add a new minor mode `glyphless-display-mode'
    
    * doc/emacs/display.texi (Text Display): Mention it.
    
    * doc/lispref/display.texi (Glyphless Chars): Document it.
    * lisp/textmodes/glyphless-mode.el: New minor mode (bug#27544).
---
 doc/emacs/display.texi           |  6 ++++
 doc/lispref/display.texi         |  7 +++++
 etc/NEWS                         |  4 +++
 lisp/textmodes/glyphless-mode.el | 67 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 84 insertions(+)

diff --git a/doc/emacs/display.texi b/doc/emacs/display.texi
index 90044b1..0230a28 100644
--- a/doc/emacs/display.texi
+++ b/doc/emacs/display.texi
@@ -1673,6 +1673,12 @@ characters more prominent on display.  @xref{Glyphless 
Chars,,
 Glyphless Character Display, elisp, The Emacs Lisp Reference Manual},
 for details.
 
+@findex glyphless-display-mode
+  The @code{glyphless-display-mode} minor mode can be used to toggle
+the display of glyphless characters in the current buffer.  The
+glyphless characters will be displayed as boxes with acronyms of their
+names inside.
+
 @cindex curly quotes, and terminal capabilities
 @cindex curved quotes, and terminal capabilities
 @cindex @code{homoglyph} face
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index f37b351..275c15e 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -8193,7 +8193,14 @@ there is no available font (on a graphical display), and 
characters
 which cannot be encoded by the terminal's coding system (on a text
 terminal).
 
+@vindex glyphless-display-mode
+The @code{glyphless-display-mode} minor mode can be used to toggle
+displaying glyphless characters in a convenient manner in the current
+buffer.  If this mode is enabled, all the glyphless characters are
+displayed as boxes that display acronyms of their character names.
+
 @defvar glyphless-char-display
+For more fine-grained (and global) control, this variable can be used.
 The value of this variable is a char-table which defines glyphless
 characters and how they are displayed.  Each entry must be one of the
 following display methods:
diff --git a/etc/NEWS b/etc/NEWS
index 352d189..e30ad60 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -295,6 +295,10 @@ received.
 
 * Changes in Specialized Modes and Packages in Emacs 29.1
 
+** New minor mode 'glyphless-display-mode'.
+This allows an easy way to toggle seeing all glyphless characters in
+the current buffer.
+
 ** Registers
 
 +++
diff --git a/lisp/textmodes/glyphless-mode.el b/lisp/textmodes/glyphless-mode.el
new file mode 100644
index 0000000..3aeb360
--- /dev/null
+++ b/lisp/textmodes/glyphless-mode.el
@@ -0,0 +1,67 @@
+;;; glyphless-mode.el --- minor mode for displaying glyphless characters  -*- 
lexical-binding: t; -*-
+
+;; Copyright (C) 2021 Free Software Foundation, Inc.
+
+;; Maintainer: emacs-devel@gnu.org
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;; Code:
+
+(defcustom glyphless-mode-types '(all)
+  "Which glyphless characters to display.
+The value can be any of the groups supported by
+`glyphless-char-display-control' (which see), and in addition
+`all', for all glyphless characters."
+  :version "29.1"
+  :type '(repeat (choice (const :tag "All" all)
+                         (const :tag "No font" no-font)
+                         (const :tag "C0 Control" c0-control)
+                         (const :tag "C1 Control" c1-control)
+                         (const :tag "Format Control" format-control)
+                         (const :tag "Variation Selectors" variation-selectors)
+                         (const :tag "No Font" no-font)))
+  :group 'display)
+
+;;;###autoload
+(define-minor-mode glyphless-display-mode
+  "Minor mode for displaying glyphless characters in the current buffer.
+If enabled, all glyphless characters will be displayed as boxes
+that display their acronyms."
+  :lighter " Glyphless"
+  (if glyphless-display-mode
+      (progn
+        (setq-local glyphless-char-display
+                    (let ((table (make-display-table)))
+                      (set-char-table-parent table glyphless-char-display)
+                      table))
+        (glyphless-mode--setup))
+    (kill-local-variable 'glyphless-char-display)))
+
+(defun glyphless-mode--setup ()
+  (let ((types (if (memq 'all glyphless-mode-types)
+                   '(c0-control c1-control format-control
+                                variation-selectors no-font)
+                 glyphless-mode-types)))
+    (when types
+      (update-glyphless-char-display
+       nil (mapcar (lambda (e) (cons e 'acronym)) types)))))
+
+(provide 'glyphless-mode)
+
+;;; glyphless-mode.el ends here