these 3 derivations will be built:
  /nix/store/kk7xnlaw6c8ywhmdbdnr505lbmcvw5h5-source.drv
  /nix/store/8iyswa4sidi2zbq5bhw1psvqyc2m8mpn-harmonia-deps-3.2.0.drv
  /nix/store/nkq99k11mjxdnypiknlyjikxw17h49qw-harmonia-llvm-cov-3.2.0.drv