bug#4587: Antwort: Re: bug#4587: 23.1; sort-lines and sort-fields always set buffer modified

[Kevin Rodgers]

Stefan Monnier wrote:
> > > I'd indeed expect that to implement the feature you request, the code
> > > would have to do something like that.  Most likely not copying the text
> > > itself, but instead storing an md5 or somesuch hash of the text.
>
> > Not suitable for Emacs, but maybe useful for Roland:
>
> > (defadvice sort-lines (around restore-buffer-modified-p activate)
> >   (let* ((buffer-was-modified-p (buffer-modified-p))
> >          (buffer-was-not-modified-md5 (if (not buffer-was-modified-p)
> >                                           (md5 (current-buffer)))))
> >     ad-do-it
> >     (when (and (not buffer-was-modified-p)
> >                (buffer-modified-p)
> >                (not (equal buffer-was-not-modified-md5 (md5 (current-buffer)))))
> >       (restore-buffer-modified-p buffer-was-modified-p))))
>
> Maybe we could make it suitable, turn it into a macro and use it around
> the various candidates.  AFAICT, here are the problems I see with it:
> - the call to md5 should use as much as possible the internal encoding.
>   I.e. at least pass an `emacs-internal' arg, tho it would be even
>   better to let md5 work directly on the internal representation.
> - it should only work on the afected region rather than the whole buffer
>   (i.e. it needs start..end arguments).
> - should it fiddle with the undo list?  or even revert the whole
>   "without-effect" set of changes (the changes may result in the same
>   final text, but they may very well have moved markers and changed
>   text-properties, and it might be desirable to undo those changes, so
>   as to better pretend nothing happened).

Is this what you have in mind?

(defmacro with-maybe-region-modified (beg end &rest body)
  "Execute BODY, then `restore-buffer-modified-p' if the contents are unchanged.
BODY should not change the current buffer or modify the contents outside the 
region
between BEG and END."
  `(let* ((region-beg ,beg)
          (region-end ,end)
          (buffer-was-modified-p (buffer-modified-p))
          (buffer-was-not-modified-md5 (if (not buffer-was-modified-p)
                                           (md5 (current-buffer) region-beg 
region-end
                                                'emacs-mule)))
          ;; (orig-buffer-undo-list buffer-undo-list)
          (with-maybe-region-modified-result
           (progn ,@body)))             ; save-current-buffer?
     (when (and (not buffer-was-modified-p)
                (buffer-modified-p)
                (not (equal buffer-was-not-modified-md5
                            (md5 (current-buffer) region-beg region-end
                                 'emacs-mule))))
       (restore-buffer-modified-p buffer-was-modified-p)
       ;; (setq buffer-undo-list orig-buffer-undo-list)
       )
     with-maybe-region-modified-result))


--
Kevin Rodgers
Denver, Colorado, USA