[PATCH v5] org.el: Warning for unsupported markers in `org-set-emphasis-alist'

[Ihor Radchenko]

Ihor Radchenko <yantar92@posteo.net> writes:

>> I think, verbatim option should not be removed from `defcustom' :type 
>> just now. For some users it might cause fallback to raw lisp value in 
>> easy customization UI. Perhaps another warning should be added to the 
>> `org-set-emphasis-alist' validator and the option should be labeled as 
>> unused in the :type definition.
>
> Makes sense.
> What about the attached patch?
> The idea is to tag the constant as deprecated.

I further improved the patch adding variable watcher. This should catch
everything. See the attached.

Let me know if there are any objections.

>From 78c61c6cc6fe95ab4d661c86ee8b3902a499cd0e Mon Sep 17 00:00:00 2001
Message-Id: 
<78c61c6cc6fe95ab4d661c86ee8b3902a499cd0e.1675335125.git.yantar92@posteo.net>
From: Max Nikulin <manikulin@gmail.com>
Date: Mon, 22 Nov 2021 23:56:15 +0700
Subject: [PATCH v5] org.el: Warn about unsupported markers in
 `org-set-emphasis-alist'

* lisp/org.el (org-emphasis-alist): Change custom variable type
definition.  Remove unused third list entry from the default value.

(org-emphasis-alist--check-value): New function used to warn the user
when unsupported value is set.  The function is used via
`add-variable-watcher'.

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

Link: https://orgmode.org/list/878rxoa6lk.fsf@localhost
---
 lisp/org.el | 56 ++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 45 insertions(+), 11 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index 1947c63a8..bc879e5d7 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -3635,8 +3635,27 @@ (defvar org-verbatim-re nil
 
 (defvar org-emphasis-regexp-components) ; defined just below
 (defvar org-emphasis-alist) ; defined just below
+(defun org-emphasis-alist--check-value (symbol value &optional operation _)
+  "Verify the VALUE of `org-emphasis-alist' SYMBOL.
+Issue a warning when the value is not supported.
+Optional argument OPERATION is intended for `add-variable-watcher'
+usage, which see."
+  (when (memq operation '(set let))
+    (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 symbol))))))
 (defun org-set-emph-re (var val)
-  "Set variable and compute the emphasis regular expression."
+  "Set VAR to VAL and compute the emphasis regular expression.
+The function is intended for :set argument of `defcustom' for
+`org-emphasis-alist'."
   (set-default-toplevel-value var val)
   (when (and (boundp 'org-emphasis-alist)
             (boundp 'org-emphasis-regexp-components)
@@ -3674,12 +3693,13 @@ (defvar org-emphasis-regexp-components
 
 You need to reload Org or to restart Emacs after setting this.")
 
+(add-variable-watcher 'org-emphasis-alist #'org-emphasis-alist--check-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,
@@ -3687,18 +3707,32 @@ (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")
+  :package-version '(Org . "9.7")
   :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"))
+           (option (const :tag "Deprecated ignored constant" verbatim)))))
 
 (defvar org-protecting-blocks '("src" "example" "export")
   "Blocks that contain text that is quoted, i.e. not processed as Org syntax.
-- 
2.39.1


-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>