Subject: Re: 26.0.60; Problem with mkdir() on root drive (ms-windows)

From: Paul Eggert <[email-masked]>
Date: Tue, 19 Sep 2017 01:50:59 -0700

Thanks for reporting that. I installed the attached patch into the emacs-26 branch.
>From 3c8da733879cd9c9ffd3b4709b596589f79f4fdf Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email-masked]>
Date: Tue, 19 Sep 2017 01:47:39 -0700
Subject: [PATCH] Fix bug with make-directory on MS-Windows root

* lisp/files.el (files--ensure-directory): Treat any error, not
just file-already-exists, as an opportunity to check whether DIR
is already a directory (Bug#28508).
---
 lisp/files.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/files.el b/lisp/files.el
index ff0ab70..0c30d40 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -5337,7 +5337,7 @@ files--ensure-directory
   "Make directory DIR if it is not already a directory.  Return nil."
   (condition-case err
       (make-directory-internal dir)
-    (file-already-exists
+    (error
      (unless (file-directory-p dir)
        (signal (car err) (cdr err))))))
 
-- 
2.7.4