bug#18141: 24.4.50; saving .gz file breaks file coding

[Vincent Lefevre <vincent@vinc17.net>]

On 2014-08-06 20:32:27 +0300, Eli Zaretskii wrote:
> > (Emacs seems to be confused on files that have several encodings,
> > such as mailboxes)
> 
> It does?  I didn't see that since Emacs 23.1 at the least.

Things may have been fixed. I don't remember exactly. There's also
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13505 that was fixed
not so long ago.

> > and I sometimes hit Ctrl-C in the terminal (from which Emacs was
> > started) to discard any change.
> 
> Then don't do that, if it hurts.

Ctrl-C is standard to interrupt a foreground process. If the process
can't handle that, it should trap SIGINT. Ditto for SIGQUIT. But
processes must handle SIGHUP and SIGTERM gracefully, ditto for various
errors, like an X server crash.

> C-g or M-~ or C-/ in Emacs will discard changes (in different
> scenarios) without any adverse effects, as will killing the buffer
> that visits the modified file. Why brutally abort Emacs by a signal,
> when Emacs gives you better ways to do that?

I haven't see any better way. My goal is to quit Emacs, discarding any
change. Ctrl-C in the terminal is the fastest way to do that.

> > And that's not OK to only leave the backup file,
> > since it can be removed or overwritten pretty quickly, before
> > I notice that the original file is gone.
> 
> Removed or overwritten by whom or what?

By me. I sometimes get rid of all the backup files because I don't need
them, since the original file should have been kept. A backup file is
overwritten if I edit a file of the same name in another directory, and
again, this is normally not a problem.

> > But why isn't the backup done just before the file is actually
> > written?
> 
> It _is_ done "just before", see basic-save-buffer-2.

No, not without r111638: the backup is done before the user is asked
to the provide an encoding, thus not just before the file is written.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)