UncanonicalizedIter can generate invalid paths if the path has a dash or hyphen within the first 4 characters.

Example, my-tool produces:

• my/-t/my-tool
• my/_t/my-tool
• my/-t/my_tool
• my/_t/my_tool

The second and third paths are invalid because the directory prefix does not match the name of the file.

I think the UncanonicalizedIter needs to iterate over the fs_name before it has been converted to path.