bug#22795: 25.0.91; Can't write read only file on w32

[Eli Zaretskii]

> Date: Mon, 29 Feb 2016 13:34:36 -0800
> CC: <22795@debbugs.gnu.org>
> From: "Ota, Takaaki" <Takaaki.Ota@am.sony.com>
> 
> I just tried again with "run -Q" from gdb and the result is the same.
> 24.5 never called sys_rename() and 25.0.91 called sys_rename() with
> two same names.

What about Frename_file? does 24.5 call it in this scenario?

If it doesn't, then please look at the beginning of backup-buffer (in
files.el), make sure it is called in 24.5 in this scenario, and then
please tell what are the values of real-file-name and backup-info in
this part at the beginning of backup-buffer:

        (let* ((real-file-name (file-chase-links buffer-file-name))
               (backup-info (find-backup-file-name real-file-name)))

Also, what are the values of make-backup-files, backup-inhibited, and
buffer-backed-up in the buffer that visits the read-only file?

Btw, is that file under some kind of version control, per chance?

And please make sure, from now on, to test everything in "emacs -Q",
to prevent any customizations from getting in the way of this
investigation.

Thanks.