org-display-inline-images doesn't work for denote: links about denote

[protesilaos]

This is a bug in Org, as it hardcodes what type of link can preview an image. I modified the relevant function just to prove the concept (I SIMPLIFIED IT AND IT SHOULD NOT BE USED AS-IS):

(defun org-display-inline-images (&optional include-linked refresh beg end)
  "Display inline images.

An inline image is a link which follows either of these
conventions:

  1. Its path is a file with an extension matching return value
     from `image-file-name-regexp' and it has no contents.

  2. Its description consists in a single link of the previous
     type.  In this case, that link must be a well-formed plain
     or angle link, i.e., it must have an explicit \"file\" or
     \"attachment\" type.

Equip each image with the key-map `image-map'.

When optional argument INCLUDE-LINKED is non-nil, also links with
a text description part will be inlined.  This can be nice for
a quick look at those images, but it does not reflect what
exported files will look like.

When optional argument REFRESH is non-nil, refresh existing
images between BEG and END.  This will create new image displays
only if necessary.

BEG and END define the considered part.  They default to the
buffer boundaries with possible narrowing."
  (interactive "P")
  (when (display-graphic-p)
    (when refresh
      (org-remove-inline-images beg end)
      (when (fboundp 'clear-image-cache) (clear-image-cache)))
    (let ((end (or end (point-max))))
      (org-with-point-at (or beg (point-min))
        (let* ((case-fold-search t)
               (file-extension-re (image-file-name-regexp))
               (link-abbrevs (mapcar #'car
                                     (append org-link-abbrev-alist-local
                                             org-link-abbrev-alist)))
               ;; Check absolute, relative file names and explicit
               ;; "file:" links.  Also check link abbreviations since
               ;; some might expand to "file" links.
               (file-types-re
                (format "\\[\\[\\(?:file%s:\\|denote:\\|attachment:\\|[./~]\\)\\|\\]\\[\\(<?\\(?:file\\|denote\\|attachment\\):\\)"
                        (if (not link-abbrevs) ""
                          (concat "\\|" (regexp-opt link-abbrevs))))))
          (while (re-search-forward file-types-re end t)
            (let* ((link (org-element-lineage
                          (save-match-data (org-element-context))
                          '(link) t))
                   (linktype (org-element-property :type link))
                   (inner-start (match-beginning 1))
                   (path
                    (cond
                     ((equal "denote" linktype)
                      (org-element-property :path link))
                     ;; No link at point; no inline image.
                     ((not link) nil)
                     ;; File link without a description.  Also handle
                     ;; INCLUDE-LINKED here since it should have
                     ;; precedence over the next case.  I.e., if link
                     ;; contains filenames in both the path and the
                     ;; description, prioritize the path only when
                     ;; INCLUDE-LINKED is non-nil.
                     ((or (not (org-element-property :contents-begin link))
                          include-linked)
                      (and (or (equal "file" linktype)
                               (equal "attachment" linktype))
                           (org-element-property :path link)))
                     ;; Link with a description.  Check if description
                     ;; is a filename.  Even if Org doesn't have syntax
                     ;; for those -- clickable image -- constructs, fake
                     ;; them, as in `org-export-insert-image-links'.
                     ((not inner-start) nil)
                     (t
                      (org-with-point-at inner-start
                        (and (looking-at
                              (if (char-equal ?< (char-after inner-start))
                                  org-link-angle-re
                                org-link-plain-re))
                             ;; File name must fill the whole
                             ;; description.
                             (= (org-element-property :contents-end link)
                                (match-end 0))
                             (progn
                               (setq linktype (match-string 1))
                               (match-string 2))))))))
              (when path
                (let ((file (cond
                             ((equal "denote" linktype)
                              (denote-link--ol-resolve-link-to-target path))
                             ((equal "attachment" linktype)
                              (require 'org-attach)
                              (ignore-errors (org-attach-expand path)))
                             (t
                              (expand-file-name path)))))
                  (when file
                    (let ((width (org-display-inline-image--width link))
                          (old (get-char-property-and-overlay
                                (org-element-property :begin link)
                                'org-image-overlay)))
                      (if (and (car-safe old) refresh)
                          (image-flush (overlay-get (cdr old) 'display))
                        (let ((image (org--create-inline-image file width)))
                          (when image
                            (let ((ov (make-overlay
                                       (org-element-property :begin link)
                                       (progn
                                         (goto-char
                                          (org-element-property :end link))
                                         (skip-chars-backward " \t")
                                         (point)))))
                              ;; FIXME: See bug#59902.  We cannot rely
                              ;; on Emacs to update image if the file
                              ;; has changed.
                              (image-flush image)
                              (overlay-put ov 'display image)
                              (overlay-put ov 'face 'default)
                              (overlay-put ov 'org-image-overlay t)
                              (overlay-put
                               ov 'modification-hooks
                               (list 'org-display-inline-remove-overlay))
                              (when (boundp 'image-map)
                                (overlay-put ov 'keymap image-map))
                              (push ov org-inline-image-overlays))))))))))))))))

What we need is for the Org link infrastructure to provide a property that handles image previewing. We will then add support for it. The function org-display-inline-images will have to be updated accordingly to handle the path resolution scheme of custom links, instead of hardcoding the file or attachment types.

I do not have time to report this as a bug in Org, nor to prepare the relevant patch. I am happy to help if someone takes the initiative.

[protesilaos]

Oh, this is interesting! I will check how Org handles images and report back to you.