dired-do-rename on "." and ".."

[Markus Rost]

Create directories "~/a" "~/b".  Open a dired buffer for "~/a":

===Buffer a=================================================
  /home/rost/a:
  total used in directory 8 available 194651436
  drwxr-xr-x   2 rost     regfacul     4096 Jun  1 22:33 .
  drwx--x--x  62 rost     regfacul     4096 Jun  1 22:33 ..

============================================================

Put cursor on "." and hit key "R" (which runs the command
dired-do-rename).  Answer "~/b" to the prompt:

==> Rename . to: ~/b

I would expect that directory "~/a" would then be renamed to "~/b/a",
as it happens when do (dired-do-rename "~/a" -> "~/b) in a dired
buffer of "~/".  However, instead you get the query

==> Overwrite `/home/rost/b'? [Type yn!q or C-h] 

This makes you suspicious, you quit, and no harm was done.  But
suppose you answer "y".  Then you get an error message:

==> dired-rename-subdir-2: Expected to find `/home/rost/a/./' in
headerline of /home/rost/a/

In fact, directory "~/b" had been deleted and "~/a" has been renamed
to "~/b".  At least if "~/b" was empty.  The dired buffer looks now
like this:

===Buffer a=================================================
  /home/rost/a:
  total used in directory 8 available 194651436
  drwx--x--x  62 rost     regfacul     4096 Jun  1 22:33 ..

============================================================

Typing "g" yields an error:

==> apply: Setting current directory: no such file or directory, ~/a/

If "~/b" is not empty, you get an error:

Move `/home/rost/a/.' to `/home/rost/b' failed:
(file-already-exists File exists /home/rost/a /home/rost/b)

and no harm was done.

I think one should fix this.  The minimum would be to disallow
renaming of ".".  Better perhaps, allow renaming "." to some other
directory, like renaming a subdirectory, and then update the dired
buffer with the new path.


OK, here it comes worse:  Try to rename "..":  Create directory
"~/a/c", open the dired buffer for it, put cursor on "..", hit "R",
and answer "~/b".  You are prompted with

Overwrite `/home/rost'? [Type yn!q or C-h] 

Panic...  Fortunately no harm will done if you answer "y".  Still, one
should fix this and perhaps disallow renaming of "..".