Globally unique internal links exported by org mode

Table of Contents

Problem

Org mode when exporting to html auto generates internal links by the sequence number, e.g. #orgheadline23. It causes a few problems:

  1. If multiple blog posts are posted on the same html page, like word press home page, internal links are not unique.
  2. Links change when re-exporting the document and you re-ordered some entries.
  3. Even if it is possible to add the custom heading via CUSTOM_ID property, it’s cumbersome to generate it for all headings. Auto-generating it with yasnippet would not be backwards compatible.

Solution

Stick this anywhere in your Emacs config. This post demos this behaviour. It replaces internal org function:

(defun org-export-get-reference (datum info)
  "My version of unique org headline."
  (let ((type (org-element-type datum))
        (cache (or (plist-get info :internal-references)
                   (let ((h (make-hash-table :test #'eq)))
                     (plist-put info :internal-references h)
                     h)))
        (auto-headline (replace-regexp-in-string "[^a-zA-Z0-9]+" "-" (org-element-property :raw-value datum)))
        )
    (or (gethash datum cache)
        (puthash datum auto-headline cache))))

The function generating new headlines is simply the:

(replace-regexp-in-string "[^a-zA-Z0-9]+" "-" (org-element-property :raw-value datum))

When I have time I may try to make it less hacky and merge it with upstream. It simply picks current heading org mode heading title, only leaves alphanumeric characters and replaces everything else with a single -. Works well for all of my org files and it’s “backward compatible” comparing to solutions like auto-generating CUSTOM_ID via yasnippet.

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