Re: Quitting `save-buffer' loses backup file

[Sven Joachim]

Richard M. Stallman wrote:

> I am going through mail that I failed to deal with earlier.
> Please forgive the delay.
>
>     $ echo "foo" > bar ; cp bar bar~
>     $ emacs -Q -f view-hello-file bar
>
>     In Emacs, in the "bar" buffer, type
>
>     M-x insert-buffer RET
>     C-x C-s
>
>     Emacs should display a '*Warning*' buffer now; type C-g to quit.
>     Now `buffer-backed-up' is t, but the backup file bar~ is gone. :-(
>
> When I try it, I find that bar~ exists but bar is gone.
> And buffer-backed-up is nil.

Humm.  This does not look quite right either.  In which directory did you
try this?  It makes a difference if you try in your
temporary-file-directory, since Emacs does not make backups there.

> Does it still fail for you the same as before?

As of the latest Debian snapshot (dated 2005-12-21), yes.  Has anybody
worked on it since then?

Because there had been no response here, I reported the issue to the
Debian bug tracking system and had an interesting discussion with
Romain which can be found at http://bugs.debian.org/343705.

Here is a summary of what Emacs does in the scenario:

(a) Before saving bar, Emacs renames bar to bar~, overwriting the old
    backup in the process, and sets `buffer-backed-up' to t.  This is
    documented in the manual.

(b) Emacs tries to save bar but fails to do so, because the user quits.
    To reduce harm, Emacs renames bar~ back to bar.  But -- and this is
    probably wrong -- Emacs does not set `buffer-backed-up' back to nil.