GNU bug report logs - #54542
29.0.50; dired can't visit a local directory if another buffer visits an unreachable remote (TRAMP) directory

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Dima Kogan <dima <at> secretsauce.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.0.50; dired can't visit a local directory if another buffer
 visits an unreachable remote (TRAMP) directory
Date: Thu, 24 Mar 2022 00:15:10 -0700

Hi. This sounds convoluted, but it's a real-life bug I hit repeatedly.
Recipe:

1. emacs -Q

2. C-x C-f /ssh:host:directory

   Visit some remote directory via TRAMP. This opens a dired buffer

3. Unplug the network cable. Or walk away from wifi. Or turn off the
   remote host. Optionally, do other stuff with emacs. The bug is hit if
   the buffer in step 2 is open somewhere; doesn't have to be visible

4. C-x C-f /some/local/directory

One would expect step 4 to work just fine because it's a local
directory, so no TRAMP business should affect it, but it does. Step 4
will try to connect to the host in step 2. But that host is gone, so
it'll fail, and step 4 will fail too.

The problem is here:

  (defun dired-find-buffer-nocreate (dirname &optional mode)
      ....
      (let (found (blist dired-buffers))
        ...
        (while blist
            ...
            (with-current-buffer (cdr (car blist))
            ....
                              (expand-file-name
                               (if (consp dired-directory)
                                   (car dired-directory)
                                 dired-directory))))

Here dired is trying to figure out if we're already visiting the
requested directory. In doing so, it loops through all extant dired
buffers, and runs (expand-file-name) on each one. Running
(expand-file-name) on a remote directory will try to contact the host.

I'm not attaching a patch because I'm not 100% sure what's appropriate.
I guess we want to replace

  (expand-file-name dired-directory)

with something like this pseudo-code

  (concat (tramp-host dired-directory)
          (expand-file-name (tramp-filename dired-directory)))

Except, thinking about edge cases: making sure this works with/without
TRAMP, making sure relative directories work right, etc, etc.

Do we already have a function that does this?

Thanks!

Message #8 received at 54542 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Dima Kogan <dima <at> secretsauce.net>
Cc: 54542 <at> debbugs.gnu.org
Subject: Re: bug#54542: 29.0.50; dired can't visit a local directory if
 another buffer visits an unreachable remote (TRAMP) directory
Date: Fri, 25 Mar 2022 17:23:45 +0100

[Message part 1 (text/plain, inline)]

Dima Kogan <dima <at> secretsauce.net> writes:

Hi Dima,

> 1. emacs -Q
>
> 2. C-x C-f /ssh:host:directory
>
>    Visit some remote directory via TRAMP. This opens a dired buffer
>
> 3. Unplug the network cable. Or walk away from wifi. Or turn off the
>    remote host. Optionally, do other stuff with emacs. The bug is hit if
>    the buffer in step 2 is open somewhere; doesn't have to be visible
>
> 4. C-x C-f /some/local/directory
>
> One would expect step 4 to work just fine because it's a local
> directory, so no TRAMP business should affect it, but it does. Step 4
> will try to connect to the host in step 2. But that host is gone, so
> it'll fail, and step 4 will fail too.
>
> The problem is here:
>
>   (defun dired-find-buffer-nocreate (dirname &optional mode)
>       ....
>       (let (found (blist dired-buffers))
>         ...
>         (while blist
>             ...
>             (with-current-buffer (cdr (car blist))
>             ....
>                               (expand-file-name
>                                (if (consp dired-directory)
>                                    (car dired-directory)
>                                  dired-directory))))
>
> Here dired is trying to figure out if we're already visiting the
> requested directory. In doing so, it loops through all extant dired
> buffers, and runs (expand-file-name) on each one. Running
> (expand-file-name) on a remote directory will try to contact the host.
>
> I'm not attaching a patch because I'm not 100% sure what's appropriate.
> I guess we want to replace
>
>   (expand-file-name dired-directory)
>
> with something like this pseudo-code
>
>   (concat (tramp-host dired-directory)
>           (expand-file-name (tramp-filename dired-directory)))
>
> Except, thinking about edge cases: making sure this works with/without
> TRAMP, making sure relative directories work right, etc, etc.
>
> Do we already have a function that does this?

We have already variable non-essential, which shall help for
non-existing / broken connections. While I could reproduce your initial
recipe locally, the attached patch cures it for me. Could you, please,
test?

> Thanks!

Best regards, Michael.

[Message part 2 (text/x-patch, attachment)]

Message #11 received at 54542 <at> debbugs.gnu.org (full text, mbox):

From: Dima Kogan <dima <at> secretsauce.net>
To: Michael Albinus <michael.albinus <at> gmx.de>
Cc: 54542 <at> debbugs.gnu.org
Subject: Re: bug#54542: 29.0.50; dired can't visit a local directory if
 another buffer visits an unreachable remote (TRAMP) directory
Date: Fri, 25 Mar 2022 16:15:34 -0700

Michael Albinus <michael.albinus <at> gmx.de> writes:

> We have already variable non-essential, which shall help for
> non-existing / broken connections. While I could reproduce your
> initial recipe locally, the attached patch cures it for me. Could you,
> please, test?

Hi Michael. Your patch fixes the issue. Thanks for looking into this!

Message #16 received at 54542-done <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: Dima Kogan <dima <at> secretsauce.net>
Cc: 54542-done <at> debbugs.gnu.org
Subject: Re: bug#54542: 29.0.50; dired can't visit a local directory if
 another buffer visits an unreachable remote (TRAMP) directory
Date: Sat, 26 Mar 2022 11:57:59 +0100

Version: 29.1

Dima Kogan <dima <at> secretsauce.net> writes:

Hi Dima,

>> We have already variable non-essential, which shall help for
>> non-existing / broken connections. While I could reproduce your
>> initial recipe locally, the attached patch cures it for me. Could you,
>> please, test?
>
> Hi Michael. Your patch fixes the issue. Thanks for looking into this!

Thanks for the feedback. I've committed this to Emacs master, closing
the bug.

Best regards, Michael.

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