these 3 derivations will be built:
  /nix/store/0lazgfhdb0ca62943zprgxqmxvwqmr5k-source.drv
  /nix/store/jgbadqs3f8b7m99vqgrc1nnahz8i8c8r-harmonia-deps-3.1.0.drv
  /nix/store/f6hrjgm5fgjy0182rsd3kfwl6vc9zfvp-harmonia-llvm-cov-3.1.0.drv