bug#57102: 29.0.50; Peculiar file-name-split edge case

[Philip Kaludercic <philipk@posteo.net>]

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I am not sure if this is intentional, but the new `file-name-split'
is a bit unintuitive in this edge-case:

   (file-name-split "/")        → ("" "" "")

while

   (file-name-split "/a")       → ("" "a")
   (file-name-split "a/")       → ("a" "")
   (file-name-split "a/b")      → ("a" "b")

another few peculiar cases might be

   (file-name-split "//")       → ("/" "" "")
   (file-name-split "///")      → ("" "" "")
   (file-name-split "////")     → ("" "" "")

as I'd expect '/' (in the first case) to never be part of a file name
(at least on a *nix system).

This all appears to happen only if there is no actual file name to be
found:

   (file-name-split "a/")       → ("a" "")
   (file-name-split "a//")      → ("a" "")
   (file-name-split "a///")     → ("a" "")

One simple solution might just be to remove all empty strings from the
return value of `file-name-split', as to my knowledge empty file names
are now allowed (?):


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diff --git a/lisp/files.el b/lisp/files.el
index 65f9039b33..c5817be8da 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -5170,7 +5170,7 @@ file-name-split
                   (substring dir 0 -1))
                 components)
           (setq filename nil))))
-    components))
+    (delq "" components)))
 
 (defun file-parent-directory (filename)
   "Return the directory name of the parent directory of FILENAME.

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That should take care of all the inconsistencies I see here, and it
would also preserve the usual intuition that "path///to//file"
designates the same path as "path/to/file".

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34, cairo version 1.17.6)
 of 2022-08-01 built on rhea
Repository revision: 47f1cae83c269ea43d6b208e055ce536c017856f
Repository branch: feature/package+vc
System Description: Fedora Linux 36 (Workstation Edition)

Configured using:
 'configure --with-pgtk --with-native-compilation --with-imagemagick'

Configured features:
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