GNU bug report logs - #21931
25.0.50; behaviour of read-directory-name with double slashes

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Nicolas Richard <youngfrog <at> members.fsf.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.50; behaviour of read-directory-name with double slashes
Date: Mon, 16 Nov 2015 07:27:51 +0100

After I eval:
(let ((default-directory "/tmp"))
  (list (read-directory-name "foo" "/tmp/src/")
        (read-directory-name "foo" "/tmp/src//")
        (read-directory-name "foo" "src/")
        (read-directory-name "foo" "src//")
        (read-directory-name "foo" "foo//src/")
        (read-directory-name "foo" "foo//src//")))
and hit RET RET RET RET, I get :
("/tmp/src/" "/" "src/" "/" "/src/" "/")

Is this intended ?

We could normalize the directory name via expand-file-name in all cases,
e.g. :

modified   lisp/files.el
@@ -648,8 +648,7 @@ read-directory-name
   (unless dir
     (setq dir default-directory))
   (read-file-name prompt dir (or default-dirname
-				 (if initial (expand-file-name initial dir)
-				   dir))
+				 (expand-file-name (or initial "") dir))
 		  mustmatch initial
 		  'file-directory-p))

but the docstring states "Value is not expanded---you must call
`expand-file-name' yourself." so I guess the behaviour is important (and
I guess e.g. for tramp).

Should read-file-name be fixed or should the callers make sure to not
use double slashes ?

In GNU Emacs 25.0.50.1 (i686-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2015-11-14
Repository revision: ed2e7e20ae0945288c98091f308f5460c3453873
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04.3 LTS

Message #8 received at 21931 <at> debbugs.gnu.org (full text, mbox):

From: John Wiegley <jwiegley <at> gmail.com>
To: Nicolas Richard <youngfrog <at> members.fsf.org>
Cc: 21931 <at> debbugs.gnu.org
Subject: Re: bug#21931: 25.0.50;
 behaviour of read-directory-name with double slashes
Date: Fri, 20 Nov 2015 11:19:27 -0800

>>>>> Nicolas Richard <youngfrog <at> members.fsf.org> writes:

> ("/tmp/src/" "/" "src/" "/" "/src/" "/")
> Is this intended ?

What list were you expecting to see? "//" has always meant "start at root" to
mean, ignoring whatever comes prior. This is how C-x C-f works, and it means
you don't have to delete any existing default text in order to begin at root.

John

Message #13 received at 21931-done <at> debbugs.gnu.org (full text, mbox):

From: Nicolas Richard <youngfrog <at> members.fsf.org>
To: John Wiegley <jwiegley <at> gmail.com>
Cc: 21931-done <at> debbugs.gnu.org
Subject: Re: bug#21931: 25.0.50;
 behaviour of read-directory-name with double slashes
Date: Mon, 23 Nov 2015 15:14:59 +0100

John Wiegley writes:
>>>>>> Nicolas Richard <youngfrog <at> members.fsf.org> writes:
>
>> ("/tmp/src/" "/" "src/" "/" "/src/" "/")
>> Is this intended ?
>
> What list were you expecting to see? "//" has always meant "start at root" to
> mean, ignoring whatever comes prior. This is how C-x C-f works, and it means
> you don't have to delete any existing default text in order to begin at root.

Indeed, but when constructing a path via (concat foo "/" bar), it can
happen that the result contains //. If this is then used as arg to
read-directory-name, this leads to an unexpected default.

OTOH (info "(elisp) Directory Names") explicitly says that using concat
for constructing paths in this way is wrong, so I guess that this bug
report is void.

Thanks for looking into it, I close it.

Nico.

Message #16 received at 21931 <at> debbugs.gnu.org (full text, mbox):

From: Michael Albinus <michael.albinus <at> gmx.de>
To: 21931 <at> debbugs.gnu.org
Cc: youngfrog <at> members.fsf.org
Subject: Re: bug#21931: 25.0.50;
 behaviour of read-directory-name with double slashes
Date: Mon, 23 Nov 2015 21:58:28 +0100

Nicolas Richard <youngfrog <at> members.fsf.org> writes:

>> What list were you expecting to see? "//" has always meant "start at root" to
>> mean, ignoring whatever comes prior. This is how C-x C-f works, and it means
>> you don't have to delete any existing default text in order to begin at root.
>
> Indeed, but when constructing a path via (concat foo "/" bar), it can
> happen that the result contains //. If this is then used as arg to
> read-directory-name, this leads to an unexpected default.

(expand-file-name bar foo) is your choice. If you dislike it, take
(concat (directory-file-name foo) "/" bar)

> Thanks for looking into it, I close it.
>
> Nico.

Best regards, Michael.

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