self.outPath
self.sourceInfo.outPath
It would be incorrect to say that the `sourceInfo` has an `outPath` that isn't the root. `sourceInfo` is about the root, whereas only the flake may not be about the root. Thanks Eelco for pointing that out.
self.outPath == ./.
Users expect `self` to refer to the directory where the `flake.nix` file resides.