roceed; you edit at your own (and the other user's) risk.
You can uit; don't modify this file.")
(with-current-buffer standard-output
(help-mode))))
(define-error 'file-supersession nil 'file-error)
(defun userlock--check-content-unchanged (fn)
(with-demoted-errors "Unchanged content check: %S"
;; Even tho we receive `fn', we know that `fn' refers to the current
;; buffer's file.
(cl-assert (equal fn (expand-file-name buffer-file-truename)))
;; Note: rather than read the file and compare to the buffer, we could save
;; the buffer and compare to the file, but for encrypted data this
;; wouldn't work well (and would risk exposing the data).
(save-restriction
(widen)
(let ((buf (current-buffer))
(cs buffer-file-coding-system)
(start (point-min))
(end (point-max)))
;; FIXME: To avoid a slow `insert-file-contents' on large or
;; remote files, it'd be good to include file size in the
;; "visited-modtime" check.
(when (with-temp-buffer
(let ((coding-system-for-read cs)
(non-essential t))
(insert-file-contents fn))
(when (= (buffer-size) (- end start)) ;Minor optimization.
(= 0 (let ((case-fold-search nil))
(compare-buffer-substrings
buf start end
(current-buffer) (point-min) (point-max))))))
(set-visited-file-modtime)
'unchanged)))))
;;;###autoload
(defun userlock--ask-user-about-supersession-threat (fn)
;; Called from filelock.c.
(unless (userlock--check-content-unchanged fn)
(ask-user-about-supersession-threat fn)))
;;;###autoload
(defun ask-user-about-supersession-threat (fn)
"Ask a user who is about to modify an obsolete buffer what to do.
This function has two choices: it can return, in which case the modification
of the buffer will proceed, or it can (signal \\='file-supersession (file)),
in which case the proposed buffer modification will not be made.
You can rewrite this to use any criterion you like to choose which one to do.
The buffer in question is current when this function is called."
(discard-input)
(save-window-excursion
(let ((prompt
(format "%s changed on disk; \
really edit the buffer? (y, n, r or C-h) "
(file-name-nondirectory fn)))
(choices '(?y ?n ?r ?? ?\C-h))
answer)
(when noninteractive
(message "%s" prompt)
(error "Cannot resolve conflict in batch mode"))
(while (null answer)
(setq answer (read-char-choice prompt choices))
(cond ((memq answer '(?? ?\C-h))
(ask-user-about-supersession-help)
(setq answer nil))
((eq answer ?r)
;; Ask for confirmation if buffer modified
(revert-buffer nil (not (buffer-modified-p)))
(signal 'file-supersession
(list "File reverted" fn)))
((eq answer ?n)
(signal 'file-supersession
(list "File changed on disk" fn)))))
(message
"File on disk now will become a backup file if you save these changes.")
(setq buffer-backed-up nil))))
(defun ask-user-about-supersession-help ()
(with-output-to-temp-buffer "*Help*"
(princ
(substitute-command-keys
"You want to modify a buffer whose disk file has changed
since you last read it in or saved it with this buffer.
If you say `y' to go ahead and modify this buffer,
you risk ruining the work of whoever rewrote the file.
If you say `r' to revert, the contents of the buffer are refreshed
from the file on disk.
If you say `n', the change you started to make will be aborted.
Usually, you should type `n' and then `\\[revert-buffer]',
to get the latest version of the file, then make the change again."))
(with-current-buffer standard-output
(help-mode))))
;;; userlock.el ends here