Problem at backup-buffer for writable files in not writable dirs

[JUAN-LEON Lahoz Garcia]

Hi,

When you edit and save a writable file in a non writable dir, and you
have `backup-by-copying' to nil (the default), backup-buffer fails to
make a backup in the place user has defined with variable
`backup-directory-alist' (because you cannot move files that are in a
not writable dir, despite of file ownership), so it copies it to file
"~/%backup%~".

[ I know having writable files in non writable files is not very
 usual, but I have to edit some conf files in such directories and I
 got this ~/%backup%~ file around all the time ]

IMHO this one-liner patch solves the problem, by detecting this
situation as one of the cases where a copy should be used to backup
the file instead of moving. You may want to review and/or apply it.

Regards
juanleon

--- files.el.ori        Thu Mar 10 09:29:31 2005
+++ files.el    Thu Mar 10 10:02:00 2005
@@ -2686,6 +2686,7 @@
                             backup-by-copying
                             ;; Don't rename a suid or sgid file.
                             (and modes (< 0 (logand modes #o6000)))
+                             (not (file-writable-p (file-name-directory 
real-file-name)))
                             (and backup-by-copying-when-linked
                                  (> (file-nlinks real-file-name) 1))
                             (and (or backup-by-copying-when-mismatch