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

[Kevin Rodgers <kevin.d.rodgers@gmail.com>]

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