bug#23871: 25.1.50; Undo unexpectedly leads to blank buffer

[Phillip Lord]

Markus Triska <triska@metalevel.at> writes:

> phillip.lord@russet.org.uk (Phillip Lord) writes:
>
>> The following patch (attempts) to address the issue which is,
>> unfortunately, a bit more extensive than the last.
>
> Your patch leads to the following regression though:
>
> 1) Download bc.el from:
>
>    https://www.metalevel.at/ei/bc.el
>
> 2) emacs -Q bc.el
>
> 3) Press: C-M-x C-/
>
> 4) Point is unexpectedly placed at the end of the buffer.
>    Without your patch, point is placed at the beginning.



As an aside, probably would have been easier to include this in the
original message, rather than add a link.

bc.el looks like this:

(let ((p (start-process "bc" (current-buffer) "bc")))
  (process-send-string p "2^10\n")
  (goto-char (point-max)))

The strange thing here is that it's not specifically an undo problem.
Point doesn't move after eval-defun. You don't need to do undo to see
the difference.

This on the other hand:

(let ((p (start-process "bc" (current-buffer) "bc")))
  (process-send-string p "2^10\n")
  (sit-for 1)
  (goto-char (point-max)))

Works fine.

I will investigate.

Phil