1

Can Emacs determine the time of the last change (or the last edit) done to the current buffer?

The buffer may has been saved or not.

3

Use the standard change hooks to record that information: https://www.gnu.org/software/emacs/manual/html_node/elisp/Change-Hooks.html#Change-Hooks

If you record it, make sure it's in a buffer-local variable, so each buffer can have its own value.

Here's a sample implementation:

(defvar buffer-last-change-time nil "The last change time")
(make-variable-buffer-local 'buffer-last-change-time)

(defun buffer-record-last-change-time (beg end len)
  (setq buffer-last-change-time (current-time))
  (message (format-time-string "Recorded last change time as %F %T"
                               buffer-last-change-time)))

(add-to-list 'after-change-functions 'buffer-record-last-change-time)

Evaluate this in any buffer. Sample output:

Recorded last change time as 2015-02-02 16:00:59
Recorded last change time as 2015-02-02 16:01:00
Recorded last change time as 2015-02-02 16:01:01 [4 times]

This can probably be turned into a more general facility, if you're up to the challenge :)

  • All right, code added. I hope it helps, but don't be afraid of playing with Emacs a bit. – Ted Zlatanov Feb 2 '15 at 21:05
2

As far as I know, Emacs does not record this information (automatically). As @TedZlatanov suggested, you can record it yourself, however.

What Emacs does record is the number of changes since the buffer was last saved. See functions buffer-modified-tick and buffer-chars-modified-tick.

(I'm not sure how functions set-buffer-modified-p and not-modified affect the tick count, but my guess is that they reset it to 0. This is not specified in the Elisp manual - you would need to consult the C-code implementation to find out.)

For a buffer visiting a file, you can get the info of the last buffer save, and the last file modification, but not the last buffer modification, using function file-attributes.

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