Re: (expand-file-name "/..")

Marcus Harnisch writes:

 > I think you are getting the even/odd pattern. Beware of path names
 > that have parent references beyond root! This oscillating pattern is
 > particularly annoying when you traversing directory trees to find
 > project root directories or similar tasks.

If (expand-file-name "/..") -> "/.." as currently[1], I see two ways
that we could go.  One is to assume that in fact there is a superroot
(as on Windows, where there is a drive letter before the filesystem
root, but nothing before that, so (expand-file-name "/../..") -> "/.." 
as well.  The alternative would be to assume that it might be "turtles
all the way down," so (expand-file-name "/../..") -> "/../..",
(expand-file-name "/../../..") -> "/../../..", and so on.  I suppose
you prefer the former, but feel free to tell me otherwise.

One thing we could potentially do would be to rethink the
functionality, decide what The Right Thing is based on 25 years of
experience with expand-file-name, implement that and call it
"canonicalize-file-name".  I'm not sure that would be all that
beneficial, though, and I don't know that we have enough non-POSIX-
filesytem-semantics expertise lying around to decide what to do with
it.

Another possibility would be to see if we can hijack URL
canonicalization (which has well-known rules), but I suspect that
doesn't help with Windows, since Windows network servers don't expose
device names as far as I know.


Footnotes: 
[1]  For GNU Emacs compatibility.