these 4 derivations will be built:
  /nix/store/0lnha7gx452x59aqmpf49xgc2gbr01gz-Cargo.toml.drv
  /nix/store/irrr91l52cdvh41pyf00h4g0hmx9n05m-source.drv
  /nix/store/mh1snja3j02rv7z6rf0crg9zbsfg3jx1-harmonia-deps-3.2.0.drv
  /nix/store/95nxjvb4xv87dkq01nzhzxsdx19pzxw8-harmonia-llvm-cov-3.2.0.drv