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

[Stefan Monnier]

> --- lisp/files.el~0   2014-06-29 06:54:20 +0300
> +++ lisp/files.el     2014-08-06 17:26:42 +0300
> @@ -4835,13 +4835,17 @@
>                                                  (nth 1 setmodes)))
>                (set-file-modes buffer-file-name
>                                (logior (car setmodes) 128))))))
> -     (let (success)
> +     (let ((filename-is-magic (find-file-name-handler buffer-file-name
> +                                                      'write-region))
> +           success)
>         (unwind-protect
>                  ;; Pass in nil&nil rather than point-min&max to indicate
>                  ;; we're saving the buffer rather than just a region.
>                  ;; write-region-annotate-functions may make us of it.
> -           (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, but I'm having a hard
time seeing why the above is "right".  IOW it seems like an ugly
workaround which may itself come with unintended consequences.


        Stefan