Re: disabling undo boundaries

[Phillip Lord]

Stefan Monnier <address@hidden> writes:

>>> Could you describe the exact case that bothers you, so we could start by
>>> thinking what should be the ideal behavior for that one?
>> Yes. Any after-change-function that changes another buffer breaks undo.
>> My "noisy-change" package which just logs the before and
>> after-change-function args is an example of this.
>> https://raw.githubusercontent.com/phillord/lentic/master/noisy-change.el
>> My real use case is lentic.
>> Ideal behaviour: is just not to do it. Uncommenting all the
>> "undo_boundary" calls in undo.c seems to achieve this for me, although
>> obviously that's a blunt fix.
>
> Could you be more specific.  Give a very concrete example of a sequence
> of commands, and then explain which the undo-boundaries end up being and
> what they should be instead.


Yes, okay.

So, in *scratch* I remove comments from the second and third line and
put everything onto one line.

;; This buffer is for notes you don't want to save, and for Lisp evaluation. If 
you want to create a file, visit that file with C-x C-f, then enter the text in 
that file's own buffer.


I load noisy-change.el (but not enable it).

(setq buffer-undo-list nil)
M-x fill-paragraph (with point on the one line)

(nil
 (156 . 159)
 (#(" " 0 1
    (fontified nil face
               (whitespace-line font-lock-comment-face)))
  . -156)
 (nil face nil 155 . 156)
 (155 . 156)
 (78 . 81)
 (#(" " 0 1
    (fontified nil face font-lock-comment-face))
  . -78)
 (#<marker
  (moves after insertion)
  at 81 in *scratch*> . 1)
 (#<marker
  (moves after insertion)
  at 81 in *scratch*> . 1)
 (#<marker
  (moves after insertion)
  at 81 in *scratch*> . 1)
 (#<marker
  (moves after insertion)
  at 81 in *scratch*> . 1)
 (nil face nil 77 . 78)
 (77 . 78))

M-x undo
(setq noisy-change-undo t)
(setq buffer-undo-list nil)

M-x fill-paragraph

(nil
 (156 . 159)
 nil
 (#(" " 0 1
    (fontified nil face
               (whitespace-line font-lock-comment-face)))
  . -156)
 nil
 (nil face nil 155 . 156)
 nil
 (155 . 156)
 nil
 (78 . 81)
 nil
 (#(" " 0 1
    (fontified nil face font-lock-comment-face))
  . -78)
 nil
 (nil face nil 77 . 78)
 nil
 (77 . 78))

At my count it takes 8 undo operations to undo "fill-paragraph".
Obviously, a longer paragraph will take more operations.

Phil