bug#29440: Tramp put drive_c in the backup file name when backuping in local PC/windows

[Michael Albinus <michael.albinus@gmx.de>]

Shuguang Sun <shuguang@gmail.com> writes:

> Hi,

Hi,

> backup-directory-alist:
>      ("\\.[rR]\\(md\\)?$" . "~/.emacs.d/autosave/Rfiles")
>
> When I open a file in tramp and edit it, the backup file will be and
> was backuped in the local direcory: ~/.emacs.d/autosave/Rfiles
> (c:/Users/username/HOME/.emacs.d/autosave/Rfiles). However the
> backfile is named
> "c:/Users/username/HOME/.emacs.d/autosave/Rfiles/!drive_c!plink!!username@host!!!opt!bee!home!username!test!coxph_bench.r.~2~",
> where "dirve_c" was put in.

I've hijacked a Windows 7 machine today. It runs Emacs 25.1 only, but
this should be good enough. I have prepared a similar setting, with

--8<---------------cut here---------------start------------->8---
backup-directory-alist is a variable defined in `files.el'.
Its value is (("." . "c:/Users/lb01177/AppData/Roaming/.emacs.d/backup"))
--8<---------------cut here---------------end--------------->8---

I have used file "/plink:albinus@192.168.178.30:/home/albinus/tmp/123" as
test file. The interesting function is make-backup-file-name-1, which
I debug.

When I enter line 4422, the (when (memq system-type '(windows-nt ms-dos cygwin))
part, backup-directory is
"c:/Users/lb01177/AppData/Roaming/.emacs.d/backup", and file is still
"/plink:albinus@192.168.178.30:/home/albinus/tmp/123". As expected.

The interesting part is here:

--8<---------------cut here---------------start------------->8---
	      ;; Replace any invalid file-name characters (for the
	      ;; case of backing up remote files).
	      (setq file
		    (expand-file-name (convert-standard-filename file)))
--8<---------------cut here---------------end--------------->8---

(convert-standard-filename file) returns "\\plink!albinus@192.168.178.30!\\home\\albinus\\tmp\\123".
And (expand-file-name ...) returns then "c:/plink!albinus@192.168.178.30!/home/albinus/tmp/123".

Unexpected, indeed. I believe, this must be fixed, because "c:" is
converted to "/drive_c" later on. The final backup name is
"c:/Users/lb01177/AppData/Roaming/.emacs.d/backup/!drive_c!plink!!albinus@192.168.178.30!!!home!albinus!tmp!123.~3~"

Eli?

Best regards, Michael.