bug#38707: dired-do-rename doesn't check for "/" !

bug#38707: dired-do-rename doesn't check for "/" !

[積丹尼 Dan Jacobson]

R runs the command dired-do-rename (found in dired-mode-map), which is
an interactive autoloaded compiled Lisp function in ‘dired-aux.el’.

But it has a big bug.

Let's say you tell it to rename qqq to "xxx/yyy/zzz/".

And it works.

You get xxx/yyy/zzz/qqq

But if there is no directory zzz,
then one day you will discover you got

xxx/yyy/qqq .

Real "mv" doesn't have this bug.

$ mv k /tmp/p/
mv: cannot create regular file '/tmp/p/': Not a directory

dired-do-rename perhaps under the hood does the "mv" action, but instead
of reporting the failure, tries again with the final slash removed!

emacs-version "26.3"

bug#38707: dired-do-rename doesn't check for "/" !

[Nick Helm]

Dan Jacobson <jidanni@jidanni.org> writes:

> Let's say you tell it to rename qqq to "xxx/yyy/zzz/".
>
> And it works.
>
> You get xxx/yyy/zzz/qqq
>
> But if there is no directory zzz,
> then one day you will discover you got
>
> xxx/yyy/qqq .

I'm not sure this is actually a bug, but it looks like the behaviour
happens because of these lines in dired-do-create-files.

;; rename-file bombs when moving directories unless we do this:
(or into-dir (setq target (directory-file-name target)))

Dired could check for and issue an error in the case where the source is
a file and the target appears to be a non-existent directory. Something
like this perhaps?

--- a/lisp/dired-aux.el	2019-12-23 15:12:26.000000000 +1300
+++ b/lisp/dired-aux.el	2019-12-23 15:18:17.000000000 +1300
@@ -1878,6 +1878,10 @@
 	(apply (car into-dir) operation rfn-list fn-list target (cdr into-dir))
       (if (not (or dired-one-file into-dir))
 	  (error "Marked %s: target must be a directory: %s" operation target))
+      (if (and (not (file-directory-p (car fn-list)))
+               (not (file-directory-p target))
+               (directory-name-p target))
+          (error "%s: Target directory does not exist: %s" operation target))
       ;; rename-file bombs when moving directories unless we do this:
       (or into-dir (setq target (directory-file-name target)))
       (dired-create-files

Nick

bug#38707: dired-do-rename doesn't check for "/" !

[Lars Ingebrigtsen]

Nick Helm <nick@tenpoint.co.nz> writes:

> Dired could check for and issue an error in the case where the source is
> a file and the target appears to be a non-existent directory. Something
> like this perhaps?

[...]

> +      (if (and (not (file-directory-p (car fn-list)))
> +               (not (file-directory-p target))
> +               (directory-name-p target))
> +          (error "%s: Target directory does not exist: %s" operation target))

I think this makes sense, so I've applied it to Emacs 28.1.  However, it
is a slight behavioural change -- previously you could enter, say
"/tmp/bar/" (when moving one file), and it would move the file to the
file "/tmp/bar".

I think the new behaviour is better (i.e., bugging out), but if people
complain for some reason, then it should perhaps be reverted.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no