cp: wrong target path on Windows

I called cp -r W:/ \\Mac\Home\Download\dumb and the program told me W:\id.dat and W:\id.dat are the same file.

Here is some extra infos I got from debugging:

When calling cp -r W:/ \\Mac\Home\Download\dumb, I find something wrong in copydir::Entry::new : all source_relative, source_absolute, descendant and local_to_target are equal to "W:/"

This is because context.root_parent is None so get_local_to_root_parent takes the root of source_absolute. On UNIX system, this is fine because the whole system and devices are accessible from the root / (so it's a unique root system) but in the case of Windows, there are several roots (e.g. A:/, B:/, C:/, even \\ for remote folders).

Note that when calling cp -r W:/* \\Mac\Home\Download\dumb (note the glob star), paths are good because context.root_parent is Some with W:/.

So i think a fix about multiple roots case on Windows, like for example in get_local_to_root_parent when root_parent is None, remove the {Letter}:{Slash} if found.

Start by reading copydir::Entry::new and get_local_to_root_parent, then reproduce cp -r W:/ \\Mac\Home\Download\dumb on Windows. Trace how a missing context.root_parent is converted into a root path, and verify that drive-letter roots remain distinct and the command no longer reports the source and destination as the same file.