these 3 derivations will be built:
  /nix/store/9plig19aap4910n4wc756gvdi2ylzshc-source.drv
  /nix/store/i4iciicd6c9wwmdg09pfa8hqd6b3kwmb-harmonia-deps-3.3.0.drv
  /nix/store/l3bk5l2y6zhzz6wqc5pbwcqymk9x3n01-harmonia-llvm-cov-3.3.0.drv