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

[Lars Ingebrigtsen]

Philip Kaludercic <philipk@posteo.net> writes:

> 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")

The logic is that

(equal (string-join (file-name-split foo) "/") foo)

is supposed to be always true.  I see that's not the case in the "/"
case, so that needs fixing.