these 3 derivations will be built:
  /nix/store/l09xdfh9x5zd8k5yz43kqskdzi3d1syy-source.drv
  /nix/store/0p1vfa95izyn2amlak83appjbgmyjrqq-harmonia-deps-3.2.0.drv
  /nix/store/g921r7lphzjzf880l3a5if1iai3bkrdq-harmonia-llvm-cov-3.2.0.drv