bug#25209: 25.1; can't delete *Shell Command Output*

bug#25209: 25.1; can't delete *Shell Command Output*

[Francesco Potortì]

I don't have any idea on how to reproduce this on a fresh Emacs, but
I'll report anyway.

On a long-running multi-tty Emacs, at one point the *Shell Command
Output* buffer refuses to go away.

If I try to kill it, nothing happens, whether the current buffer is that
one or any other one.  The contents of the *Shell Command Output* buffer
are always visible in the minibuffer.  So, to make it unobtrusive, I
need to issue an
 M-! echo -n RET
every time the *Shell Command Output* buffer is dirtied.

I am still running that Emacs, so I can try to debug something.  If you
suggest me where to look, I can do that when I have time (probably not
it nthe next few days).



In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2016-10-24, modified by Debian built on trouble
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:	Debian GNU/Linux testing (stretch)

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Recent messages:
No following nondeleted message
Expunging deleted messages...done
Showing message 855...
Saving file /home/pot/Mail/RMAIL...
Wrote /home/pot/Mail/RMAIL [2 times]
Auto-saving...
Saving file /home/pot/doc/todo...
Wrote /home/pot/doc/todo
Quit [2 times]
user-error: End of history; no default available [2 times]

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bug#25209: 25.1; can't delete *Shell Command Output*

[Eli Zaretskii]

> Date: Thu, 15 Dec 2016 17:34:23 +0100
> From: Francesco Potortì <pot@gnu.org>
> 
> On a long-running multi-tty Emacs, at one point the *Shell Command
> Output* buffer refuses to go away.
> 
> If I try to kill it, nothing happens, whether the current buffer is that
> one or any other one.  The contents of the *Shell Command Output* buffer
> are always visible in the minibuffer.  So, to make it unobtrusive, I
> need to issue an
>  M-! echo -n RET
> every time the *Shell Command Output* buffer is dirtied.
> 
> I am still running that Emacs, so I can try to debug something.  If you
> suggest me where to look, I can do that when I have time (probably not
> it nthe next few days).

Some questions come to mind, hopefully one of them will help you:

Are you in recursive edit level, perhaps?

When the cursor is shown in that buffer in the echo area, does typing
C-g or "C-x o" get you out of that, and can you then kill that buffer?
Or maybe try "C-x b" to switch to a minibuffer in that situation.

Do you have some non-nil kill-buffer-hook, and if so, what does that
do?  What about kill-buffer-query-functions -- any non-nil value for
that?

What happens if you set debug-on-error non-nil, and then try to kill
that buffer?  What errors, if any, pop up, and what do they show?

When you attempt to kill the buffer, do you see any messages added to
*Messages*?

The most promising lead, IMO, is the one about this buffer being shown
in the echo area: kill-buffer won't kill the current minibuffer
buffer, so I think you should try to break that link.  Thus the first
2 questions above are the most probable cause of your trouble.

bug#25209: 25.1; can't delete *Shell Command Output*

[Francesco Potortì]

>> Date: Thu, 15 Dec 2016 17:34:23 +0100
>> From: Francesco Potortì <pot@gnu.org>
>> 
>> On a long-running multi-tty Emacs, at one point the *Shell Command
>> Output* buffer refuses to go away.
>> 
>> If I try to kill it, nothing happens, whether the current buffer is that
>> one or any other one.  The contents of the *Shell Command Output* buffer
>> are always visible in the minibuffer.  So, to make it unobtrusive, I
>> need to issue an
>>  M-! echo -n RET
>> every time the *Shell Command Output* buffer is dirtied.
>> 
>> I am still running that Emacs, so I can try to debug something.  If you
>> suggest me where to look, I can do that when I have time (probably not
>> it nthe next few days).
>
>Some questions come to mind, hopefully one of them will help you:
>
>Are you in recursive edit level, perhaps?

No :(

>When the cursor is shown in that buffer in the echo area, does typing
>C-g or "C-x o" get you out of that, and can you then kill that buffer?
>Or maybe try "C-x b" to switch to a minibuffer in that situation.

The echo area always shows the contents of the *Shell Command Output*
buffer.  When I use the minibuffer, all is well and the minibuffer works
as usual.  As soon as I finish using it, it again displays the *Shell
Command Output* buffer.  The cursor never goes there, C-x o does nothing
as usual if I have a single buffer int he window.

Oh, note that I have two frames open, one running under screen in a
virtual terminal and one on X.  Only the latter frame exhibits the
problem.

However, I have just tried to go to the terminal frame, switch to the
*Shell Command Output* buffer, and now the problem also happens there!

>Do you have some non-nil kill-buffer-hook, and if so, what does that
>do?

(tramp-flush-file-function browse-url-delete-temp-file
 preview-kill-buffer-cleanup rmail-mode-kill-summary
 tramp-delete-temp-file-function uniquify-kill-buffer-function
 vc-kill-buffer-hook)

> What about kill-buffer-query-functions -- any non-nil value for
>that?

(process-kill-buffer-query-function)
 
>What happens if you set debug-on-error non-nil, and then try to kill
>that buffer?  What errors, if any, pop up, and what do they show?

No errors...

>When you attempt to kill the buffer, do you see any messages added to
>*Messages*?

Nothing

>The most promising lead, IMO, is the one about this buffer being shown
>in the echo area: kill-buffer won't kill the current minibuffer
>buffer, so I think you should try to break that link.  Thus the first
>2 questions above are the most probable cause of your trouble.

Unfortunately I had already tried all your suggestions.  I had not
thought about the hooks, but now that I look at them I would say that I
have not set them myself and they look like standard ones.

I can obviously disregard this, kill Emacs and start a fresh one, but
maybe there is a bug lurking somewhere and this is a unique chance to
hunt it down :)

bug#25209: 25.1; can't delete *Shell Command Output*

[Andreas Schwab]

On Dez 15 2016, Francesco Potortì <pot@gnu.org> wrote:

> On a long-running multi-tty Emacs, at one point the *Shell Command
> Output* buffer refuses to go away.
>
> If I try to kill it, nothing happens, whether the current buffer is that
> one or any other one.  The contents of the *Shell Command Output* buffer
> are always visible in the minibuffer.  So, to make it unobtrusive, I
> need to issue an
>  M-! echo -n RET
> every time the *Shell Command Output* buffer is dirtied.

Did you perhaps quit while the output of a shell-command was being
displayed, because it took too long?  In that situation Emacs can end up
in a state where (minibuffer-window) points to the *Shell Command
Output* buffer, and kill-buffer will refuse to kill the buffer.

You can reset the minibuffer window with

(set-window-buffer (minibuffer-window) (get-buffer " *Minibuf-0*"))

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

bug#25209: 25.1; can't delete *Shell Command Output*

[Andreas Schwab]

On Dez 19 2016, Andreas Schwab <schwab@linux-m68k.org> wrote:

> On Dez 15 2016, Francesco Potortì <pot@gnu.org> wrote:
>
>> On a long-running multi-tty Emacs, at one point the *Shell Command
>> Output* buffer refuses to go away.
>>
>> If I try to kill it, nothing happens, whether the current buffer is that
>> one or any other one.  The contents of the *Shell Command Output* buffer
>> are always visible in the minibuffer.  So, to make it unobtrusive, I
>> need to issue an
>>  M-! echo -n RET
>> every time the *Shell Command Output* buffer is dirtied.
>
> Did you perhaps quit while the output of a shell-command was being
> displayed, because it took too long?  In that situation Emacs can end up
> in a state where (minibuffer-window) points to the *Shell Command
> Output* buffer, and kill-buffer will refuse to kill the buffer.

I think the problem is that vertical-motion (as called by
display-message-or-buffer via count-screen-lines) is not properly
protecting against quit when it temporarily modifies the window's
buffer.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

bug#25209: 25.1; can't delete *Shell Command Output*

[Francesco Potortì]

>> On a long-running multi-tty Emacs, at one point the *Shell Command
>> Output* buffer refuses to go away.
>>
>> If I try to kill it, nothing happens, whether the current buffer is that
>> one or any other one.  The contents of the *Shell Command Output* buffer
>> are always visible in the minibuffer.  So, to make it unobtrusive, I
>> need to issue an
>>  M-! echo -n RET
>> every time the *Shell Command Output* buffer is dirtied.
>
>Did you perhaps quit while the output of a shell-command was being
>displayed, because it took too long?

That may well be.

>				       In that situation Emacs can end up
>in a state where (minibuffer-window) points to the *Shell Command
>Output* buffer, and kill-buffer will refuse to kill the buffer.

In *scratch*:

(minibuffer-window)
#<window 2 on *Shell Command Output*>

>You can reset the minibuffer window with
>
>(set-window-buffer (minibuffer-window) (get-buffer " *Minibuf-0*"))

It worked :)

Thanks.

That said, isn't this a bug, and shouldn't it be squashed?

bug#25209: 25.1; can't delete *Shell Command Output*

[Francesco Potortì]

>On Dez 19 2016, Andreas Schwab <schwab@linux-m68k.org> wrote:
>
>> On Dez 15 2016, Francesco Potortì <pot@gnu.org> wrote:
>>
>>> On a long-running multi-tty Emacs, at one point the *Shell Command
>>> Output* buffer refuses to go away.
>>>
>>> If I try to kill it, nothing happens, whether the current buffer is that
>>> one or any other one.  The contents of the *Shell Command Output* buffer
>>> are always visible in the minibuffer.  So, to make it unobtrusive, I
>>> need to issue an
>>>  M-! echo -n RET
>>> every time the *Shell Command Output* buffer is dirtied.
>>
>> Did you perhaps quit while the output of a shell-command was being
>> displayed, because it took too long?  In that situation Emacs can end up
>> in a state where (minibuffer-window) points to the *Shell Command
>> Output* buffer, and kill-buffer will refuse to kill the buffer.
>
>I think the problem is that vertical-motion (as called by
>display-message-or-buffer via count-screen-lines) is not properly
>protecting against quit when it temporarily modifies the window's
>buffer.

I happen to use view-line-mode, if that can be of relevance.

bug#25209: 25.1; can't delete *Shell Command Output*

[Eli Zaretskii]

> Date: Mon, 19 Dec 2016 13:45:56 +0100
> From: Francesco Potortì <pot@gnu.org>
> Cc: 25209@debbugs.gnu.org
> 
> >The most promising lead, IMO, is the one about this buffer being shown
> >in the echo area: kill-buffer won't kill the current minibuffer
> >buffer, so I think you should try to break that link.  Thus the first
> >2 questions above are the most probable cause of your trouble.
> 
> Unfortunately I had already tried all your suggestions.  I had not
> thought about the hooks, but now that I look at them I would say that I
> have not set them myself and they look like standard ones.

I have no doubt that you (or some code in Emacs) somehow caused the
shell output buffer to be displayed in the minibuffer.  Emacs refuses
to kill such buffers, and that's what you see.

> I can obviously disregard this, kill Emacs and start a fresh one, but
> maybe there is a bug lurking somewhere and this is a unique chance to
> hunt it down :)

If there's a bug that causes this, it has done its thing long ago, and
our chances to hunt it down given your situation are pretty much nil.

Thanks.

bug#25209: 25.1; can't delete *Shell Command Output*

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Date: Mon, 19 Dec 2016 15:26:37 +0100
> Cc: 25209@debbugs.gnu.org
> 
> I think the problem is that vertical-motion (as called by
> display-message-or-buffer via count-screen-lines) is not properly
> protecting against quit when it temporarily modifies the window's
> buffer.

I think you are right.  Patches to fix that are welcome.

Thanks.

bug#25209: 25.1; can't delete *Shell Command Output*

[Andreas Schwab]

Fixed on master.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."