Subject: bug#57353: [PATCH] Fix parse-colon-path with UNC directory names

From: Richard Copley <[email-masked]>
Date: Tue, 23 Aug 2022 12:34:02 +0100

The function `parse-colon-path' changes the leading double slash
in a UNC path component to a single slash:

(let path (mapconcat path-separator "one" "//server/share/dir")
     (parse-colon-path path))
## -> ("one" "/server/share/dir")

A comment in `parse-colon-path' says:

;; Previous implementation used `substitute-in-file-name'
;; which collapse multiple "/" in front.  Do the same for
;; backward compatibility.

However, `substitute-in-file-name' does not do that:

(substitute-in-file-name "//foo/a/b") // -> "//foo/a/b"

There's no reason to do it in `parse-colon-path' either.
From 55eb8c37eeabf11f9fc1ec1f84c64fc234ecf59f Mon Sep 17 00:00:00 2001
From: Richard Copley <[email-masked]>
Date: Tue, 23 Aug 2022 12:11:20 +0100
Subject: [PATCH] Fix parse-colon-path with UNC directory names

* lisp/files.el (parse-colon-path): don't collapse multiple / at
beginning of path component
---
 lisp/files.el | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/lisp/files.el b/lisp/files.el
index cf2a522193..569fd0224e 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -853,13 +853,8 @@ nil (meaning `default-directory') as the associated list element."
   (when (stringp search-path)
     (let ((spath (substitute-env-vars search-path)))
       (mapcar (lambda (f)
-                (if (equal "" f) nil
-                  (let ((dir (file-name-as-directory f)))
-                    ;; Previous implementation used `substitute-in-file-name'
-                    ;; which collapse multiple "/" in front.  Do the same for
-                    ;; backward compatibility.
-                    (if (string-match "\\`/+" dir)
-                        (substring dir (1- (match-end 0))) dir))))
+                (unless (equal "" f)
+                  (file-name-as-directory f)))
               (split-string spath path-separator)))))
 
 (defun cd-absolute (dir)
-- 
2.37.0.windows.1