From 919fc426f298755886f6f3df22ce9670a7cf67c6 Mon Sep 17 00:00:00 2001
Message-Id: <919fc426f298755886f6f3df22ce9670a7cf67c6.1667544252.git.yantar92@posteo.net>
From: Max Nikulin <manikulin@gmail.com>
Date: Mon, 22 Nov 2021 23:56:15 +0700
Subject: [PATCH v3] org.el: Warn about unsupported markers in
 `org-set-emphasis-alist'

* lisp/org.el (org-emphasis-alist, org-set-emphasis-alist): Change
custom variable type definition and add :set parameter to warn users
that non-standard marker characters are ignored.  Remove unused third
list entry from the default value.

Attempts to introduce new markers have been discussed enough times to
add some code that should prevent wasting of time.

Unfortunately there is no way to issue warning for e.g. `setq'.

Link: https://orgmode.org/list/878rxoa6lk.fsf@localhost
---
 lisp/org.el | 50 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 42 insertions(+), 8 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index d8708f8f2..43be34daf 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -3628,12 +3628,31 @@ (defvar org-emphasis-regexp-components
 
 You need to reload Org or to restart Emacs after setting this.")
 
+(defun org-set-emphasis-alist (var value)
+  "Set VAR (`org-emphasis-alist') to VALUE.
+Warn user that Org syntax can not be extended with new emphasis
+markers if such attempt is detected.  The function is intended for
+:set argument of `defcustom'."
+  (set-default-toplevel-value var value)
+  (let ((unsupported
+	 (delq nil
+	       (mapcar
+                (lambda (entry)
+                  (let ((marker (car entry)))
+                    (unless (member marker '("*" "/" "_" "=" "~" "+")) marker)))
+                value))))
+    (when unsupported
+      (warn "Unsupported markup characters '%s' detected in `%s'"
+	    (mapconcat #'identity unsupported " ")
+	    (symbol-name var))))
+  value)
+
 (defcustom org-emphasis-alist
   '(("*" bold)
     ("/" italic)
     ("_" underline)
-    ("=" org-verbatim verbatim)
-    ("~" org-code verbatim)
+    ("=" org-verbatim)
+    ("~" org-code)
     ("+" (:strike-through t)))
   "Alist of characters and faces to emphasize text.
 Text starting and ending with a special character will be emphasized,
@@ -3641,18 +3660,33 @@ (defcustom org-emphasis-alist
 marker characters and the face to be used by font-lock for highlighting
 in Org buffers.
 
+Do not change the characters and do not add new ones to use custom
+markers for existing styles or to introduce new styles.  Org syntax is
+not meant to be configurable and such modifications will not work with
+export.
+
 You need to reload Org or to restart Emacs after customizing this."
   :group 'org-appearance
   :set 'org-set-emph-re
   :version "24.4"
   :package-version '(Org . "8.0")
+  :set #'org-set-emphasis-alist
   :type '(repeat
-	  (list
-	   (string :tag "Marker character")
-	   (choice
-	    (face :tag "Font-lock-face")
-	    (plist :tag "Face property list"))
-	   (option (const verbatim)))))
+          (group
+           (choice
+            :tag "Marker"
+            (const :tag "*Bold*" "*")
+            (const :tag "/Italic/" "/")
+            (const :tag "_Underline_" "_")
+            (const :tag "+Strike-through+" "+")
+            (const :tag "=Verbatim=" "=")
+            (const :tag "~Code~" "~")
+            ;; To warn users that it does not work.
+            (string :tag "Unsupported ignored character"))
+           (choice
+            :tag "Font"
+            (face :tag "Face")
+            (plist :tag "Property list")))))
 
 (defvar org-protecting-blocks '("src" "example" "export")
   "Blocks that contain text that is quoted, i.e. not processed as Org syntax.
-- 
2.35.1