these 3 derivations will be built:
  /nix/store/sxl4i025kygim1k7jfl15jnzv3rgm7qf-source.drv
  /nix/store/vwjdxjspvbk88mhss5z3y3j4j9sp8ayc-harmonia-deps-3.1.0.drv
  /nix/store/4zm2h2j77ifnc2xryrnc6saks6zp6580-harmonia-llvm-cov-3.1.0.drv