> Begin forwarded message:
> 
> From: Yuan Fu <casouri@gmail.com>
> Subject: Re: bug#40338: 27.0.60; c-fill-paragraph and after-change-functions
> Date: March 31, 2020 at 11:27:23 AM GMT-4
> To: Noam Postavsky <npostavs@gmail.com>
> Cc: 40338@debbugs.gnu.org
> 
> 
> 
>> On Mar 30, 2020, at 9:56 PM, Noam Postavsky <npostavs@gmail.com> wrote:
>> 
>> Yuan Fu <casouri@gmail.com> writes:
>> 
>>> (defun mytrack-hook (beg end len)
>>> (if (> len 0)
>>>     ;; delete
>>>     (with-current-buffer trackbuf
>>>       (delete-region beg (+ beg len)))
>>>   ;; insert
>>>   (let ((content (buffer-substring beg end)))
>>>     (with-current-buffer trackbuf
>>>       (goto-char beg)
>>>       (insert content)))))
>> 
>> I'm not very familiar with either eglot or cc-mode, but I can say the
>> problem in your example lies with mytrack-hook: there can be kinds of
>> changes other than just pure delete or insert (replace, for example).
>> It can be fixed like this:
>> 
>> (defun mytrack-hook (beg end len)
>> (when (> len 0)
>>   ;; Delete old text.
>>   (with-current-buffer "trackbuf"
>>     (delete-region beg (+ beg len))))
>> ;; Insert new text.
>> (let ((content (buffer-substring beg end)))
>>   (with-current-buffer "trackbuf"
>>     (goto-char beg)
>>     (insert content))))
>> 
> 
> Thank you. Indeed this works. Maybe the problem is not in c-fill-paragraph. 
> 
> Yuan