Re: [BUG] HTML export does not preserve footnote label [9.6.15 (release_9.6.15 @ /usr/local/share/emacs/30.0.50/lisp/org/)]

[Ihor Radchenko <yantar92@posteo.net>]

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Protesilaos Stavrou <info@protesilaos.com> writes:

> With regard to the disambiguation scheme, I am playing around with
> various scenaria to see how Org HTML export behaves. Using the
> following:
> ...
>     This is test 2 <sup><a id="fnr.1.100" class="footref" href="#fn.1" role="doc-backlink">1</a></sup>
> ...
>     This is test 3 <sup><a id="fnr.1.100" class="footref" href="#fn.1" role="doc-backlink">1</a></sup>
>
> Notice that the 100 in the ID is not incremented further. I guess this
> is something that can be worked on but, again, I think it is separate
> from the issue of using the label for the ID and HREF.
>
> Any thoughts?

Duplicate IDs are against HTML spec:
https://softwareengineering.stackexchange.com/questions/127178/two-html-elements-with-same-id-attribute-how-bad-is-it-really

So, this is a bug.

>>> Though I should have clarified my intent earlier: the idea is to use the
>>> label as a fixed reference to the footnote, so that the link does not
>>> change between exports. This is the same principle as what we do with
>>> links to headings that have a CUSTOM_ID.
>>>
>>> As such, the anchor text can still be the way it is now as an
>>> automatically generated number sequence (^1, ^2, etc.), but the HTML
>>> "id" and "href" values will be constructed based on the label of the
>>> footnote, NOT its number in the sequence.

See the attached tentative patch.

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From 446bfc8c8afb5b2e09d0e0acf7b136b9f0780f5a Mon Sep 17 00:00:00 2001
Message-ID: <446bfc8c8afb5b2e09d0e0acf7b136b9f0780f5a.1713016519.git.yantar92@posteo.net>
From: Ihor Radchenko <yantar92@posteo.net>
Date: Sat, 13 Apr 2024 16:53:48 +0300
Subject: [PATCH] ox-html: Use non-number footnote names as link anchors

* lisp/ox-html.el (org-html-footnote-section):
* lisp/ox-html.el (org-html-footnote-reference): When footnote has a
non-number name, build link anchors using this name.
* etc/ORG-NEWS (=ox-html=: When exporting footnotes with custom
non-number names, the names are used as link anchors): Announce the
change.

Link: https://orgmode.org/list/875xwngiwx.fsf@protesilaos.com
---
 etc/ORG-NEWS    |  8 +++++
 lisp/ox-html.el | 77 +++++++++++++++++++++++++++++--------------------
 2 files changed, 53 insertions(+), 32 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index e61bd6988..1b7040815 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -13,6 +13,14 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** Important announcements and breaking changes
+*** =ox-html=: When exporting footnotes with custom non-number names, the names are used as link anchors
+
+Previously, link anchors for footnote references and footnote
+definitions were based on the footnote number: =fn.1=, =fnr.15=, etc.
+
+Now, when the footnote has a non-number name, it is used as an anchor:
+=fn.name=, =fnr.name=.
+
 *** Underline syntax now takes priority over subscript when both are applicable
 
 Previously, Org mode interpreted =(_text_)= as subscript.
diff --git a/lisp/ox-html.el b/lisp/ox-html.el
index 0471a573b..1262da1aa 100644
--- a/lisp/ox-html.el
+++ b/lisp/ox-html.el
@@ -1873,36 +1873,42 @@ (defun org-html-footnote-section (info)
   (pcase (org-export-collect-footnote-definitions info)
     (`nil nil)
     (definitions
+     (format
+      (plist-get info :html-footnotes-section)
+      (org-html--translate "Footnotes" info)
       (format
-       (plist-get info :html-footnotes-section)
-       (org-html--translate "Footnotes" info)
-       (format
-	"\n%s\n"
-	(mapconcat
-	 (lambda (definition)
-	   (pcase definition
-	     (`(,n ,_ ,def)
-	      ;; `org-export-collect-footnote-definitions' can return
-	      ;; two kinds of footnote definitions: inline and blocks.
-	      ;; Since this should not make any difference in the HTML
-	      ;; output, we wrap the inline definitions within
-	      ;; a "footpara" class paragraph.
-	      (let ((inline? (not (org-element-map def org-element-all-elements
-				    #'identity nil t)))
-		    (anchor (org-html--anchor
-			     (format "fn.%d" n)
-			     n
-			     (format " class=\"footnum\" href=\"#fnr.%d\" role=\"doc-backlink\"" n)
-			     info))
-		    (contents (org-trim (org-export-data def info))))
-		(format "<div class=\"footdef\">%s %s</div>\n"
-			(format (plist-get info :html-footnote-format) anchor)
-			(format "<div class=\"footpara\" role=\"doc-footnote\">%s</div>"
-				(if (not inline?) contents
-				  (format "<p class=\"footpara\">%s</p>"
-					  contents))))))))
-	 definitions
-	 "\n"))))))
+       "\n%s\n"
+       (mapconcat
+	(lambda (definition)
+	  (pcase definition
+	    (`(,n ,label ,def)
+             ;; Do not assign number labels as they appear in Org mode
+             ;; - the footnotes are re-numbered by
+             ;; `org-export-get-footnote-number'.  If the label is not
+             ;; a number, keep it.
+             (when (equal label (number-to-string (string-to-number label)))
+               (setq label nil))
+	     ;; `org-export-collect-footnote-definitions' can return
+	     ;; two kinds of footnote definitions: inline and blocks.
+	     ;; Since this should not make any difference in the HTML
+	     ;; output, we wrap the inline definitions within
+	     ;; a "footpara" class paragraph.
+	     (let ((inline? (not (org-element-map def org-element-all-elements
+				 #'identity nil t)))
+		   (anchor (org-html--anchor
+			    (format "fn.%d" n)
+			    n
+			    (format " class=\"footnum\" href=\"#fnr.%s\" role=\"doc-backlink\"" (or label n))
+			    info))
+		   (contents (org-trim (org-export-data def info))))
+	       (format "<div class=\"footdef\">%s %s</div>\n"
+		       (format (plist-get info :html-footnote-format) anchor)
+		       (format "<div class=\"footpara\" role=\"doc-footnote\">%s</div>"
+			       (if (not inline?) contents
+				 (format "<p class=\"footpara\">%s</p>"
+					 contents))))))))
+	definitions
+	"\n"))))))
 
 \f
 ;;; Template
@@ -2736,8 +2742,15 @@ (defun org-html-footnote-reference (footnote-reference _contents info)
      (when (org-element-type-p prev 'footnote-reference)
        (plist-get info :html-footnote-separator)))
    (let* ((n (org-export-get-footnote-number footnote-reference info))
-	  (id (format "fnr.%d%s"
-		      n
+          (label (org-element-property :label footnote-reference))
+          ;; Do not assign number labels as they appear in Org mode -
+          ;; the footnotes are re-numbered by
+          ;; `org-export-get-footnote-number'.  If the label is not a
+          ;; number, keep it.
+          (label (if (equal label (number-to-string (string-to-number label)))
+                     nil label))
+	  (id (format "fnr.%s%s"
+		      (or label n)
 		      (if (org-export-footnote-first-reference-p
 			   footnote-reference info)
 			  ""
@@ -2745,7 +2758,7 @@ (defun org-html-footnote-reference (footnote-reference _contents info)
      (format
       (plist-get info :html-footnote-format)
       (org-html--anchor
-       id n (format " class=\"footref\" href=\"#fn.%d\" role=\"doc-backlink\"" n) info)))))
+       id n (format " class=\"footref\" href=\"#fn.%s\" role=\"doc-backlink\"" (or label n)) info)))))
 
 ;;;; Headline
 
-- 
2.44.0


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-- 
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>