these 3 derivations will be built:
  /nix/store/v3kmx5ny5rdaygh70lhl2s123pqmg2x3-source.drv
  /nix/store/8dyid13lk89j6wfl7yqlkd2z54cc6lkk-harmonia-deps-3.3.0.drv
  /nix/store/7078g2l9jz7xkz6lqvfi8q8mb39vasi5-harmonia-llvm-cov-3.3.0.drv