Find duplicate identifiers and put them in a Dired buffer

Denote takes care to create unique identifiers, though its mechanism relies on reading the existing identifiers in the denote-directory or the current directory. When we are renaming files across different directories, there is a small chance that some files have the same attributes and are thus assigned identical identifiers. If those files ever make it into a consolidated denote-directory, we will have duplicates, which break the linking mechanism.

As this is an edge case, we do not include any code to address it in the Denote code base. Though here is a way to find duplicate identifiers inside the current directory:

(defun my-denote--get-files-in-dir (directory)
  "Return file names in DIRECTORY."
  (directory-files directory :full-paths directory-files-no-dot-files-regexp))

(defun my-denote--same-identifier-p (file1 file2)
  "Return non-nil if FILE1 and FILE2 have the same identifier."
  (let ((id1 (denote-retrieve-filename-identifier file1))
        (id2 (denote-retrieve-filename-identifier file2)))
    (equal id1 id2)))

(defun my-denote-find-duplicate-identifiers (directory)
  "Find all files in DIRECTORY that need a new identifier."
  (let* ((ids (my-denote--get-files-in-dir directory))
         (unique-ids (seq-uniq ids #'my-denote--same-identifier-p)))
    (seq-difference ids unique-ids #'equal)))

(defun my-denote-dired-show-duplicate-identifiers (directory)
  "Put duplicate identifiers from DIRECTORY in a dedicated Dired buffer."
  (interactive
   (list
    (read-directory-name "Select DIRECTORY to check for duplicate identifiers: " default-directory)))
  (if-let* ((duplicates (my-denote-find-duplicate-identifiers directory)))
      (dired (cons (format "Denote duplicate identifiers" directory) duplicates))
    (message "No duplicates identifiers in `%s'" directory)))

Evaluate this code and then call the command my-denote-dired-show-duplicate-identifiers. If there are duplicates, it will put them in a dedicated Dired buffer. From there, you can view the file contents as usual, and manually edit the identifiers as you see fit (e.g. edit them one by one, or change to the writable Dired and record a keyboard macro that makes use of a counter to increment by 1—contact me if you need any help).