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From: Alan Mackenzie <acm@muc.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: Eli Zaretskii <eliz@gnu.org>, emacs-devel@gnu.org
Subject: Re: Edebug corrupting point in buffers.
Date: Tue, 1 Nov 2022 20:53:47 +0000	[thread overview]
Message-ID: <Y2GHWybprtVeF0pb@ACM> (raw)
In-Reply-To: <jwv7d0e3235.fsf-monnier+emacs@gnu.org>

Hello, Stefan.

On Tue, Nov 01, 2022 at 15:47:45 -0400, Stefan Monnier wrote:
> > Why does set-window-configuration overwrite the buffer-points?  The
> > window configuration does not contain them.  The code just assumes that
> > the buffer-point should be set to the window point.  Of course, we have
> > a race condition if a buffer is displayed in several windows.  So this
> > would appear to be a bug, the root cause of the bug in this thread.

> This suggests the patch below, right?
> I note that this only changes the buffer-point for `current-buffer`, not
> for all the buffers displayed in the window-config, right?

Not quite.  It changes the buffer-point for every buffer except the
"current buffer".

> There's still a "race condition", of course.

> > Maybe set-window-configuration should be amended not to write the
> > buffer-points?  That might cause problems in other areas, though.  The
> > window configuration is one of the few areas where the documentation is
> > poor enough that you need to read the C source to find out what it's
> > really doing.

> Yup.  We could start by providing some way to tell
> `set-window-configuration` not to change buffer-points (and use that in
> Edebug)?  This way we fix the problem for Edebug without risking
> changes elsewhere?

An &optional parameter, you mean?  I'd thought of that, but it feels
ugly.

> We can try and run out own Emacs with the patch installed, to see if we
> notice any regression.

Indeed, yes.  I count 89 occurrences of '(set-window-configuration' in
our Lisp sources.  That's not really a comfortable number to check by
looking at the code.  :-(

> If we do, that might help us understand what we should do.  If we
> don't, maybe it's hint that it was really just a bug.

It feels like a bug for the reasons already given, and the fact that the
"current buffer"'s buffer-point is spared.  If there's something wrong
with overwriting that buffer's buffer-point, why is it OK for all the
other buffers in windows in the window-configuration?

I'm going to try out your patch and see if it, by itself, fixes the bug,
now that I've got a reproducible test case.

<...later...>

I've tried it, and the patch doesn't fix the bug.  :-(  Something else
is clearly overwriting the buffer-point.

>         Stefan


> diff --git a/src/window.c b/src/window.c
> index b858d145415..382d3cbdc6a 100644
> --- a/src/window.c
> +++ b/src/window.c
> @@ -7270,12 +7270,6 @@ DEFUN ("set-window-configuration", Fset_window_configuration,
>  	      set_marker_restricted (w->start, p->start, w->contents);
>  	      set_marker_restricted (w->pointm, p->pointm, w->contents);
>  	      set_marker_restricted (w->old_pointm, p->old_pointm, w->contents);
> -	      /* As documented in Fcurrent_window_configuration, don't
> -		 restore the location of point in the buffer which was
> -		 current when the window configuration was recorded.  */
> -	      if (!EQ (p->buffer, new_current_buffer)
> -		  && XBUFFER (p->buffer) == current_buffer)
> -		Fgoto_char (w->pointm);
>  	    }
>  	  else if (BUFFERP (w->contents) && BUFFER_LIVE_P (XBUFFER (w->contents)))
>  	    /* Keep window's old buffer; make sure the markers are real.  */

-- 
Alan Mackenzie (Nuremberg, Germany).



  reply	other threads:[~2022-11-01 20:53 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-31 11:43 Edebug corrupting point in buffers; we need buffer-point and set-buffer-point, perhaps Alan Mackenzie
2022-10-31 13:16 ` Eli Zaretskii
2022-10-31 14:32   ` Alan Mackenzie
2022-10-31 14:50     ` Eli Zaretskii
2022-10-31 15:46       ` Alan Mackenzie
2022-10-31 17:33         ` Stefan Monnier
2022-10-31 17:55         ` Eli Zaretskii
2022-10-31 20:46           ` Alan Mackenzie
2022-11-01  6:21             ` Eli Zaretskii
2022-10-31 17:19       ` Stefan Monnier
2022-10-31 18:09         ` Eli Zaretskii
2022-10-31 20:35           ` Stefan Monnier
2022-10-31 17:21 ` Stefan Monnier
2022-10-31 18:10   ` Eli Zaretskii
2022-10-31 23:14     ` Stefan Monnier
2022-11-01  7:06       ` Eli Zaretskii
2022-10-31 21:25 ` Alan Mackenzie
2022-11-01  6:45   ` Eli Zaretskii
2022-11-01 11:41     ` Edebug corrupting point in buffers Alan Mackenzie
2022-11-01 11:53       ` Eli Zaretskii
2022-11-01 13:42         ` Alan Mackenzie
2022-11-01 14:42           ` Eli Zaretskii
2022-11-01 17:06             ` Alan Mackenzie
2022-11-01 17:12               ` Eli Zaretskii
2022-11-01 17:24                 ` Alan Mackenzie
2022-11-01 17:57                   ` Eli Zaretskii
2022-11-01 19:02                     ` Alan Mackenzie
2022-11-01 19:47                       ` Stefan Monnier
2022-11-01 20:53                         ` Alan Mackenzie [this message]
2022-11-01 21:51                           ` Stefan Monnier
2022-11-02 10:40                             ` Alan Mackenzie
2022-11-02 13:12                               ` Stefan Monnier
2022-11-02 13:28                                 ` Eli Zaretskii
2022-11-02  3:28                         ` Eli Zaretskii
2022-11-02 12:53                           ` Stefan Monnier
2022-11-02 17:40                       ` Juri Linkov
2022-11-02 18:26                         ` Eli Zaretskii
2022-11-02 18:36                           ` Juri Linkov
2022-11-02 18:52                             ` Eli Zaretskii
2022-11-03 17:25                               ` Juri Linkov
2022-11-03 18:06                                 ` Eli Zaretskii
2022-11-03 18:31                                   ` Juri Linkov
2022-11-02 11:34                     ` Alan Mackenzie
2022-11-02 14:00                       ` Eli Zaretskii
2022-11-02 16:18                         ` Alan Mackenzie
2022-11-02 16:57                           ` Eli Zaretskii
2022-11-03 11:32                             ` Alan Mackenzie
2022-11-03 13:29                               ` Eli Zaretskii
2022-11-03 18:07                                 ` Alan Mackenzie
2022-11-03 18:15                                   ` Eli Zaretskii
2022-11-03 20:25                                     ` Alan Mackenzie
2022-11-05 11:24                                       ` Eli Zaretskii
2022-11-05 16:50                                         ` Alan Mackenzie
2022-11-06  8:10                                           ` Eli Zaretskii
2022-11-06 14:40                                             ` Alan Mackenzie
2022-11-03 19:29                         ` Stefan Monnier
2022-11-03 19:36                           ` Eli Zaretskii
2022-11-03 20:39                             ` Stefan Monnier
2022-11-04  6:34                               ` Eli Zaretskii
2022-11-04  6:37                               ` Eli Zaretskii
2022-11-03 19:57                           ` Alan Mackenzie
2022-11-03 20:35                             ` Stefan Monnier

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