From: Eli Zaretskii <eliz@gnu.org>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: 18141@debbugs.gnu.org, vincent@vinc17.net, yamaoka@jpl.org
Subject: bug#18141: 24.4.50; saving .gz file breaks file coding
Date: Thu, 07 Aug 2014 18:14:39 +0300 [thread overview]
Message-ID: <83ha1onxgg.fsf@gnu.org> (raw)
In-Reply-To: <jwv61i5xhi4.fsf-monnier+emacsbugs@gnu.org>
> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: rgm@gnu.org, 18141@debbugs.gnu.org, vincent@vinc17.net, yamaoka@jpl.org
> Date: Wed, 06 Aug 2014 20:45:59 -0400
>
> >> > - (let ((coding-system-for-write writecoding)
> >> > - (coding-system-require-warning nil))
> >> > + (let ((coding-system-for-write
> >> > + (if filename-is-magic coding-system-for-write writecoding))
> >> > + (coding-system-require-warning
> >> > + (if filename-is-magic coding-system-require-warning)))
> >> > (write-region nil nil
> >> > buffer-file-name nil t buffer-file-truename)
> >> > (setq success t))
> >> I can vaguely guess why that avoids the problem
> > The problem is the binding of coding-system-for-write based on
> > incorrect interpretation of buffer-file-name. Why that causes the bug
> > was explained in the text you elided. The code avoids the binding,
> > and thus fixes its adverse effects.
>
> Actually, the code doesn't really avoid the binding: there's still
> a let-binding. So the variable's value is still restored when we finish.
Is that a problem, and if so, why?
We do such things in many places. I'm not aware of another way of
making a conditional let-binding of a global variable.
> Also, while I understand that the binding is wrong, I don't understand
> why the "non-binding" is right.
Because that's how it used to work before the offending commit:
write-region calls choose-write-coding-system internally. But it does
so _after_ handing any files with magic names to their handlers.
IOW, the patch I suggested simply refrains from forcing a particular
encoding in case of files that have handlers, like we did before.
> >> but I'm having a hard time seeing why the above is "right".
> > Do you see why the binding is "wrong"?
>
> The other problem I see is with the filename-is-magic condition which
> seems overly general.
Again, that's how write-region always worked. And with magic file
names, this is actually the right approach: Emacs has no idea how to
set up the encoding for such files, so it must delegate that
responsibility to the handler. choose-write-coding-system works only
for local (a.k.a. "non-magic") files, it cannot possibly DTRT for
files that have handlers.
> > As for unintended consequences, I don't see how can any come out of
> > that, since this just restores the code that was working for years.
>
> Hmm... so you're saying this reverts part of the change?
It disables the modified code for files whose names are magic, yes.
> [ I'm not very familiar with this code, in case you haven't noticed yet. ]
That's no crime, surely.
> > Of course, if you have a better suggestion that would be safe enough
> > for the release branch, I'm all ears.
>
> Don't know yet what to do for the release branch, but I suspect reverting
> is the better option since this problem has been with us for many many
> years already.
I agree, obviously.
> As for the right fix: move the backup-generation to a later point.
> This means either to split write-region into several sub-elements that
> basic-save-buffer-2 can call separately. Or to add some kind of hook to
> write-region so basic-save-buffer-2 can use it to create the backup at
> the right time.
Why not move the call to backup-buffer (and surrounding code that
deals with backup complications) from basic-save-buffer-2 to a
separate function, and then call that function directly from
write-region, right before it is about to write the new contents?
While at that, we should IMO make the backup-then-write sequence a
transaction, by using the suitable unwind-protect functions, and
perhaps also make sure that unwind-protect function runs if Emacs is
killed half-way through the sequence, to keep the transaction promise.
next prev parent reply other threads:[~2014-08-07 15:14 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-29 6:59 bug#18141: 24.4.50; saving .gz file breaks file coding Katsumi Yamaoka
2014-07-30 0:10 ` Glenn Morris
2014-07-30 2:36 ` Katsumi Yamaoka
2014-07-30 13:15 ` Katsumi Yamaoka
2014-08-05 8:34 ` Glenn Morris
2014-08-06 14:36 ` Eli Zaretskii
2014-08-06 16:43 ` Vincent Lefevre
2014-08-06 17:32 ` Eli Zaretskii
2014-08-06 19:08 ` Vincent Lefevre
2014-08-06 19:45 ` Eli Zaretskii
2014-08-07 0:31 ` Vincent Lefevre
2014-08-07 12:20 ` Stefan Monnier
2014-08-07 14:23 ` Vincent Lefevre
2014-08-11 1:06 ` Glenn Morris
2014-08-06 17:48 ` Stefan Monnier
2014-08-06 18:10 ` Eli Zaretskii
2014-08-07 0:45 ` Stefan Monnier
2014-08-07 15:14 ` Eli Zaretskii [this message]
2014-08-07 19:08 ` Stefan Monnier
2014-08-07 19:37 ` Eli Zaretskii
2014-08-07 20:43 ` Stefan Monnier
2014-08-08 5:51 ` Eli Zaretskii
2014-08-06 23:45 ` Glenn Morris
2014-08-07 0:03 ` Glenn Morris
2014-08-07 12:14 ` Stefan Monnier
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