these 3 derivations will be built:
  /nix/store/w4gc0s040nvandpn75iny92mldm4mvqd-source.drv
  /nix/store/3nr4kw73ij0hpblwb113jmji1n9clq6m-harmonia-deps-3.3.0.drv
  /nix/store/9mdy29bz2gv5rxx3zjk5hqrwnvbgcvc1-harmonia-llvm-cov-3.3.0.drv