bug#40338: 27.0.60; c-fill-paragraph and after-change-functions

bug#40338: 27.0.60; c-fill-paragraph and after-change-functions

[Yuan Fu]

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Background: I use eglot with c-mode and every time I use c-fill-paragraph, eglot breaks—it reports a syntax error when there isn’t. It seems that eglot’s image of the buffer’s content (or what it thinks is in the buffer) is corrupted. I can fix this by revert-buffer. I have a feeling that this has something to do with after-change-functions because that’s the only way eglot gets updated with buffer changes. So I setup an experiment. It goes like this:

Open track.el and eval-buffer; then go to test.c and M-: (mytrack); then open the tracking buffer “trackbuf” in another window. Now if you edit in test.c, the change should be reflected in trackbuf. Now try M-q. Both buffer ends up in a corrupted state. 

I tried to look at c-fill-paragraph but it’s too complicated. I hope someone with more expertise in c-mode could give some insight.

Yuan


[-- Attachment #2: track.el --]
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(defun mytrack ()
  (let ((content (buffer-string)))
    (with-current-buffer (get-buffer-create "trackbuf")
      (erase-buffer)
      (insert content))
    (add-hook 'after-change-functions #'mytrack-hook nil t)))

(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)))))

[-- Attachment #3: test.c --]
[-- Type: application/octet-stream, Size: 696 bytes --]

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include "dep.h"

// Writes data to the given channel
// This is a blocking call i.e., the function only returns on a successful completion of send
// In case the channel is full, the function waits till the channel has space to write the new data
// Returns SUCCESS for successfully writing data to the channel,
// CLOSED_ERROR if the channel is closed, and
// GEN_ERROR on encountering any other generic error of any sort
int add(int x, int y) {
  return x + y;
}

int main() {
  char arr[4];
  arr[0] = 'a';
  arr[1] = 'b';
  arr[2] = 'c';
  arr[3] = 'd';
  int x = 1;
  int y = -1;
  int z = 0;
  int j = add(z, y);
  return 0;
}

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In GNU Emacs 27.0.60 (build 1, x86_64-apple-darwin19.3.0, NS appkit-1894.30 Version 10.15.3 (Build 19D76))
of 2020-02-25 built on missSilver
Repository revision: f27187f963e9e36435b508e29256e048799e0ff2
Repository branch: emacs-27
Windowing system distributor 'Apple', version 10.3.1894
System Description:  Mac OS X 10.15.4

Recent messages:
Wrote /Users/yuan/Desktop/test.c
C-= is undefined
scroll-up-command: End of buffer
Mark set [3 times]
Saving file /Users/yuan/Desktop/track.el...
Wrote /Users/yuan/Desktop/track.el
mytrack-hook
(mytrack-hook)
save-current-buffer: Args out of range: #<buffer trackbuf>, 421, 422
Undo
(mytrack-hook)
Configured using:
'configure --with-modules --with-pdumper=yes
--oldincludedir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/libxml2/'

Configured features:
RSVG GLIB NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS XIM
NS MODULES THREADS PDUMPER LCMS2

Important settings:
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  value of $LANG: en_CN.UTF-8
  locale-coding-system: utf-8-unix

Major mode: C/*l

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Load-path shadows:
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text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads kqueue cocoa ns
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Memory information:
((conses 16 70716 8607)
(symbols 48 8390 1)
(strings 32 21585 1417)
(string-bytes 1 808085)
(vectors 16 12103)
(vector-slots 8 152019 12686)
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(intervals 56 999 22)
(buffers 1000 16))

bug#40338: 27.0.60; c-fill-paragraph and after-change-functions

[Noam Postavsky]

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))))

bug#40338: 27.0.60; c-fill-paragraph and after-change-functions

[Yuan Fu]

> 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

bug#40338: Fwd: bug#40338: 27.0.60; c-fill-paragraph and after-change-functions

[Yuan Fu]

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> 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


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