bug#26272: default-directory: Remark that it must be a directory name

[Tino Calancha <tino.calancha@gmail.com>]

On Mon, 27 Mar 2017, Noam Postavsky wrote:

> On Mon, Mar 27, 2017 at 2:26 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>>> From: Noam Postavsky <npostavs@users.sourceforge.net>
>>> Date: Mon, 27 Mar 2017 11:52:21 -0400
>>> Cc: Tino Calancha <tino.calancha@gmail.com>, 26272@debbugs.gnu.org
>>>
>>>>>> Didn't we discuss that at some point in the past?
>>>>> I don't remember it.  Maybe with another person.
>>>>
>>>> No, I meant on emacs-devel, not with you personally.
>>>
>>> This one maybe? (it's about load-path though)
>>> https://lists.gnu.org/archive/html/emacs-devel/2015-10/msg02060.html
>>
>> Yes, but AFAIR it also touched default-directory.
>
> Ah, it seems that code was fixed to be more tolerant: the trailing
> slash in default-directory used to matter for executing processes, but
> not any more: https://lists.gnu.org/archive/html/emacs-devel/2015-10/msg02367.html
Following is not the same but slightly related:
emacs -Q /tmp

I) OK
M-x cd RET /tmp/ RET
M-: (default-directory) RET
=> "/tmp/"

II) OK
M-x cd RET /tmp RET
M-: (default-directory) RET
=> "/tmp/"

III) Wrong
M-x cd RET /tmp// RET
M-: (default-directory) RET
=> "/"

;; Just an issue on interactive calls, as you can see:
M-: (mapcar
      (lambda (x)
        (progn (cd x) default-directory))
      '("/tmp/" "/tmp" "/tmp//")) RET
=> ("/tmp/" "/tmp/" "/tmp/")