these 4 derivations will be built:
  /nix/store/bgk49y0pqz7ikj9b37k0z9nvnf4dmlsa-Cargo.toml.drv
  /nix/store/g9jad8pzc1iaq8bfpsxamk57kk12rgmw-source.drv
  /nix/store/4afzrqwmhph45ny158ixh1xj01in3snc-harmonia-deps-3.3.0.drv
  /nix/store/jp0jygwlxdi4c4i0frhf9nlli8nlsb5l-harmonia-llvm-cov-3.3.0.drv