don't allow modification if there is autosave

Question

is it possible to disallow modification if there is an autosave version? I sometimes save a file only to find out that it has an autosave version but I am unable to recover because I saved.

Answer 1

One can derive how to detect existing autosave data from the part of after-find-file that emits the message "%s has auto save data; consider M-x recover-this-file".

Just enter read-only-mode in find-file-hook if a buffer has autosave data.

(defun my-make-auto-saved-file-read-only ()
  "Set the buffer read-only if it has a recent auto-save file."
  ;; Stolen from `after-find-file':
  (when (and 
     ;; No need to warn if buffer is auto-saved
     ;; under the name of the visited file.
     (not (and buffer-file-name
           auto-save-visited-file-name))
     (file-newer-than-file-p (or buffer-auto-save-file-name
                     (make-auto-save-file-name))
                 buffer-file-name))
    (read-only-mode)))

(add-hook 'find-file-hook #'my-make-auto-saved-file-read-only)

Note, with this approach you must reset read-only-mode yourself after reverting the file. But that is very simple in Emacs with GUI. Just click on the remaining % in the mode line.