Emacs lisp：替换缓冲区内容时保持光标位置

Question

I'm trying to fix an issue on in the web-beautify package.

An elisp function uses an external tool to reformat the content of the buffer. It then does the following, to try and keep the cursor position :

(let ((p (point)))
   (save-excursion
     (with-current-buffer (current-buffer)
       (erase-buffer)
       (insert-buffer-substring outputbuf)))
   (goto-char p)
   ...

If any line is added before the point, the (goto-char p) can cause the buffer to scroll erratically.

Following this , I tried replacing p with (create-marker (point) t) ; It does seem to handle text added at the beginning of the buffer better, in general ; however in this case, it does not work at all (presumably because the content of the buffer is completely replace.)

How would you attack this ?

Answer 1

I don't think there can be a fully general answer to this question. The notion of the place in the new text which corresponds to a particular spot in the original text completely depends on our human understanding of what the text is and how it's modified and what matters and what doesn't.

So you need to look at the kind of changes operated by the external tool and try to figure out a way to find what you consider to be the corresponding spot. Eg if the tool doesn't add/remove lines, then you can preserve the line-position, on the contrary if the tool only adds/removes lines then you can look at the text surrounding point and try to find it again in the new text.

Answer 2

Looks like replace-buffer should do the trick.

Source: https://emacs.stackexchange.com/a/47889/10669