these 3 derivations will be built:
  /nix/store/9wvkcpi2pnc9pbrrwaycdfvvcmqgxg0g-source.drv
  /nix/store/w0xr7wbd0gyjpvp1093d7jwr8799h4xn-harmonia-deps-3.2.0.drv
  /nix/store/753rdhs6v0d8w7jqajln557fdmgy20w7-harmonia-llvm-cov-3.2.0.drv