Using the path itself didn't work for me.
Here's what finally worked for me on MacOS:
cd ~/projects
git clone file:///Users/me/projects/myawesomerepo myawesomerepocopy
This also worked:
git clone file://localhost/Users/me/projects/myawesomerepo myawesomerepocopy
The path itself worked if I did this:
git clone --local myawesomerepo myawesomerepocopy