Re: save-excursion doesn't restore point with json-pretty-print

[Tassilo Horn <tsdh@gnu.org>]

Tassilo Horn <tsdh@gnu.org> writes:

> Eli Zaretskii <eliz@gnu.org> writes:
>
>>> > json-read-from-string uses a temporary buffer anyway, so a couple of
>>> > trivial changes in json-pretty-print should do the trick.
>>> 
>>> Is this what you have in mind?  Seems to work well.
>>
>> Yes.
>
> Ok, great.  Do you think it would make sense to extract the mechanics of
> narrowing, extracting from the narrowed source buffer, and injecting
> (transformed) into the temporary buffer with which to replace the source
> region into some function
>
>   (replace-region-contents beg end extract-fn inject-fn)
>
> That way, `json-pretty-print' would look like.

[...]

Nah, but almost.  This is the actual working code which I'd happily
commit if you agree:

--8<---------------cut here---------------start------------->8---
;; in subr.el (or wherever you please)
(defun replace-region-contents (beg end extract-fn inject-fn)
  "Replace the region between BEG and END using EXTRACT-FN and INJECT-FN.

The current buffer is narrowed to the region between BEG and END,
then EXTRACT-FN is called in order to extract some value.
Thereafter, INJECT-FN is called with that value in a temporary
buffer which it should populate.

Finally, the region in the source buffer is replaced with the
contents of the temporary buffer prepared by INJECT-FN using
`replace-buffer-contents'."
  (save-excursion
    (save-restriction
      (narrow-to-region beg end)
      (goto-char (point-min))
      (atomic-change-group
	(let ((source-buffer (current-buffer))
	      (extracted (funcall extract-fn)))
	  (with-temp-buffer
	    (funcall inject-fn extracted)
	    (let ((tmp-buffer (current-buffer)))
              (set-buffer source-buffer)
              (replace-buffer-contents tmp-buffer))))))))

;; in json.el
(defun json-pretty-print (begin end)
  "Pretty-print selected region."
  (interactive "r")
  (replace-region-contents
   begin end
   (lambda ()
     (let ((json-null :json-null)
	   ;; Ensure that ordering is maintained
	   (json-object-type 'alist))
       (json-read)))
   (lambda (json-obj)
     (let ((json-encoding-pretty-print t)
	   ;; Distinguish an empty objects from 'null'
	   (json-null :json-null))
       (insert (json-encode json-obj))))))
--8<---------------cut here---------------end--------------->8---

Bye,
Tassilo