Opening a new empty file shouldn't give message: File digest doesn’t match, so undo history will be discarded.

[nordlow]

One solution is

(defun undohist-recover-safe ()
  (when (file-exists-p buffer-file-name)
	(condition-case var
		(undohist-recover-1)
      (error (message "Can not recover undo history: %s" var)))))

. Another is

(defun undohist-recover-1 ()
  (let* ((buffer (current-buffer))
         (file (buffer-file-name buffer)))
	(when (file-exists-p file)
	  (let* ((undo-file (make-undohist-file-name file))
			 undo-list)
		(when (and (undohist-recover-file-p file)
				   (file-exists-p undo-file)
				   (or (null buffer-undo-list)
					   (yes-or-no-p "\
buffer-undo-list is not empty. Do you want to recover now? ")))
		  (with-temp-buffer
			(insert-file-contents undo-file)
			(goto-char (point-min))
			(let ((alist (undohist-decode (read (current-buffer)))))
			  (if (string= (md5 buffer) (assoc-default 'digest alist))
				  (setq undo-list (assoc-default 'undo-list alist))
				(message "\
File digest doesn't match, so undo history will be discarded."))))
		  (when (consp undo-list)
			(setq buffer-undo-list undo-list)))))))

.

[jcs090218]

I don't use this package for a long time. Therefore, feel free to open PRs to fix any issue you've encountered.

[nordlow]

I don't use this package for a long time. Therefore, feel free to open PRs to fix any issue you've encountered.

Ok. Do you use another package in place of undohist?

[jcs090218]

I recommend undo-tree, but I've heard it is hard for Emacs beginners. 🤔