please extend wslpath to handle network drives and the Linux filesystem

• Your Windows build number: 10.0.18922.1000

• What you're doing and what's happening:

At the moment, wslpath does not translate Windows paths to WSL paths for network drives, or to Windows paths for WSL paths outside non-network 9p filesystems.

i.e.

$ wslpath -u "Z:\test.txt"
wslpath: Z:\test.txt
[1]    742 exit 1     wslpath -u "Z:\test.txt"

and

$ wslpath -w "/usr/bin"
wslpath: /usr/bin
[1]    796 exit 1     wslpath -w "/usr/bin"

both fail.

• What's wrong / what should be happening instead:

Since both of these files are accessible from WSL, wslpath should transform the names appropriately. In the case of the Windows network drive, presumably this could be done by comparing the UNC name to /proc/mounts, which gets you the relevant mount point if that network location is available in WSL. Going the other way, wslpath could supply UNC names under \wsl$\distro for any WSL file not on a 9p filesystem.

i.e., expected output should be

$ wslpath -u "Z:\test.txt"
/mnt/z/test.txt

and

$ wslpath -w "/usr/bin"
\\wsl$\Debian\usr\bin

I'm busy hacking on getting the equivalent of emacsclient to call up my WSL-side Emacs to edit files from the Windows command prompt, and while I can write code to translate the filenames myself, this really should be part of WSL itself, I think.

Start by locating the wslpath entry point and its existing path-conversion handling, then reproduce the network-drive and /usr/bin examples from the issue. Done means both directions produce the expected /mnt/z and \wsl$\Debian forms for accessible paths, with the existing behavior preserved for other paths.