GNU bug report logs - #20659
auto-save-visited-file-name: leaks interlock files and abandons unsaved buffers

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

From: Nicolas Calderon <nicolas.calderon.asselin <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: auto-save-visited-file-name: leaks interlock files and abandons
 unsaved buffers
Date: Tue, 26 May 2015 01:38:54 -0400

Hi,

When auto-save-visited-file-name is set, emacs auto-saves directly to
file rather than a different file (#<filename>#). Unfortunately,
auto-saving does not get rid of the interlock file (symlink from
.#<filename> -> <user>@<host>.<pid>:<uid>). Since the buffer is saved
and not modified (buffer-modified-p is false, as evidenced by the
modline), emacs can be exited without the "Save file?" prompt. Leaving
emacs at this point, without making a proper save (save-buffer),
leaves the interlock files behind modifications directly to the file
rather than auto-saving.

While looking at that, I noticed something a bit more "dangerous".
Normally, auto-save-visited-file-name is only enabled upon restarting
auto-save-mode (http://www.gnu.org/software/emacs/manual/html_node/elisp/Auto_002dSaving.html),
and indeed, if auto-save-visited-file-name is set and auto-save-mode,
emacs keeps saving auto-saves under #<filename># and not directly to
file. After an auto-save though, the file is marked as not modified
(buffer_modified-p is false). At this point, if the user leaves emacs,
their file is not saved and the user is not prompted for saving!!! The
content of the file can still be recovered from the auto-save file.

--
Nicolas Calderon Asselin

Message #6 received at 20659-quiet <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 20659-quiet <at> debbugs.gnu.org
Subject: Re: bug#20659: auto-save-visited-file-name: leaks interlock files and
 abandons unsaved buffers
Date: Thu, 19 Jan 2017 15:35:04 -0500

See bug 25470.

Message #9 received at 20659 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Nicolas Calderon <nicolas.calderon.asselin <at> gmail.com>
Cc: 20659 <at> debbugs.gnu.org
Subject: Re: bug#20659: auto-save-visited-file-name: leaks interlock files
 and abandons unsaved buffers
Date: Sat, 23 Jan 2021 22:45:10 +0100

Nicolas Calderon <nicolas.calderon.asselin <at> gmail.com> writes:

> When auto-save-visited-file-name is set, emacs auto-saves directly to
> file rather than a different file (#<filename>#). Unfortunately,
> auto-saving does not get rid of the interlock file (symlink from
> .#<filename> -> <user>@<host>.<pid>:<uid>). Since the buffer is saved
> and not modified (buffer-modified-p is false, as evidenced by the
> modline), emacs can be exited without the "Save file?" prompt. Leaving
> emacs at this point, without making a proper save (save-buffer),
> leaves the interlock files behind modifications directly to the file
> rather than auto-saving.

(I'm going through old bug reports that unfortunately got no response at
the time.)

I'm not able to reproduce this bug in Emacs 28, and indeed this has all
been rewritten in 2017:

commit 4db844a4532592ed2542c05a1747dad7ed319e15
Author:     Philipp Stephani <phst <at> google.com>
AuthorDate: Sat Apr 22 20:58:38 2017 +0200

    Reimplement auto-saving to visited files
    
    This reacts to confusing behavior of 'auto-save-visited-file-name',
    cf. Bug#25478.

So I'm going to go ahead and guess that this has been fixed by now, and
I'm closing this bug report.  If there are still bugs in this area,
please respond to the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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