Default description for abbreviated links

["Kévin Le Gouguec" <kevin.legouguec@gmail.com>]

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Hello Org,

I like #+LINK keywords because they make documents self-sufficient:
anyone opening my document can follow these links or export the buffer;
they do not need to run some Elisp to add to org-link-parameters.

One thing I don't know how to customize, however, is how these links are
exported when they have no description.  Let's say I define this
abbreviation:

#+LINK: bug https://debbugs.gnu.org/

If I jot down references to [[bug:12345]] in my document, these will be
exported as:

<a href="https://debbugs.gnu.org/12345">https://debbugs.gnu.org/12345</a>

Whereas I'd prefer:

<a href="https://debbugs.gnu.org/12345">bug:12345</a>

Looking at org-element-link-parser, I see that this is because the
:contents-begin and :contents-end properties are nil, since they
correspond to an unmatched optional group in org-link-bracket-re.


I could probably customize org-link-parameters, but then my document
would not be self-sufficient anymore.  Besides, depending on the
document I might use the same abbreviation for different URLs.

Would it make sense to add a way for abbreviated links with no
description to fallback to LINKKEY:TAG[1] instead of the full URL?  If
so, what would be the best way to go about it?

(1) A single variable (e.g. org-link-abbrev-default-description), default
    nil, which a user could set to 'key-tag or just 'tag.

(2) A third entry in org-link-abbrev-alist(-local), default nil, which a
    user could set to 'key-tag or just 'tag.

(3) Something else (e.g. a new alist).

I've attached a very crude patch for (1): now if I stick this footer in
my Org files:

#+LINK: bug https://debbugs.gnu.org/
# Local variables:
# org-link-abbrev-default-description: key-tag
# end:

Then [[bug:12345]] is exported as
<a href="https://debbugs.gnu.org/12345">bug:12345</a>.


WDYT?  If the idea is sound, I will clean up the patch, clarify
docstrings, add :safe predicates and unit tests, and re-submit.

Thank you for your time.



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diff --git a/lisp/ol.el b/lisp/ol.el
index 82fc69769..fa0ade8b8 100644
--- a/lisp/ol.el
+++ b/lisp/ol.el
@@ -255,6 +255,16 @@ See the manual for examples."
 	    (`(,(pred stringp) . ,(pred stringp)) t)
 	    (_ nil))))
 
+(defcustom org-link-abbrev-default-description nil
+  "Fallback behaviour for abbreviated links with no description.
+If this is nil, do not set a description; some export backends
+will use the fully expanded link as fallback.  If 'key-tag, then
+use the abbreviated form KEY:TAG.  If 'tag, then use TAG."
+  :group 'org-link
+  :type '(choice (const :tag "None" nil)
+		 (const :tag "KEY:TAG" key-tag)
+		 (const :tag "TAG" tag)))
+
 (defgroup org-link-follow nil
   "Options concerning following links in Org mode."
   :tag "Org Follow Link"
@@ -993,6 +1003,16 @@ and then used in capture templates."
 	   if store-func
 	   collect store-func))
 
+(defun org-link-abbrev-default-desc (link)
+  (save-match-data
+    (when (string-match "^\\([^:]*\\)::?\\(.+\\)$" link)
+      (pcase org-link-abbrev-default-description
+	('nil '(nil nil))
+	('key-tag
+	 (list (match-beginning 1) (match-end 2)))
+	('tag
+	 (list (match-beginning 2) (match-end 2)))))))
+
 (defun org-link-expand-abbrev (link)
   "Replace link abbreviations in LINK string.
 Abbreviations are defined in `org-link-abbrev-alist'."
diff --git a/lisp/org-element.el b/lisp/org-element.el
index a693cb68d..a82fce52a 100644
--- a/lisp/org-element.el
+++ b/lisp/org-element.el
@@ -3146,11 +3146,19 @@ Assume point is at the beginning of the link."
 	;; (e.g., insert [[shell:ls%20*.org]] instead of
 	;; [[shell:ls *.org]], which defeats Org's focus on
 	;; simplicity.
-	(setq raw-link (org-link-expand-abbrev
-			(org-link-unescape
-			 (replace-regexp-in-string
-			  "[ \t]*\n[ \t]*" " "
-			  (match-string-no-properties 1)))))
+	(let ((link-spec (match-string-no-properties 1))
+	      (link-beg (match-beginning 1)))
+	  (setq raw-link (org-link-expand-abbrev (org-link-unescape
+						  (replace-regexp-in-string
+						   "[ \t]*\n[ \t]*" " "
+						   link-spec))))
+	  ;; If there is no description, try to find a fallback.
+	  (unless contents-begin
+	    (pcase-let ((`(,default-beg ,default-end)
+			 (org-link-abbrev-default-desc link-spec)))
+	      (when default-beg
+		(setq contents-begin (+ link-beg default-beg)
+		      contents-end (+ link-beg default-end))))))
 	;; Determine TYPE of link and set PATH accordingly.  According
 	;; to RFC 3986, remove whitespaces from URI in external links.
 	;; In internal ones, treat indentation as a single space.

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[1] Or just TAG.  If I look at ORG-NEWS for examples, I see a lot of
    [[doc:org-symbol][org-symbol]].