these 3 derivations will be built:
  /nix/store/i6q39q0l4z21vw5ah7va0kzy0f5g24f2-source.drv
  /nix/store/s0zq8ll4yqhyirjfqdi87djg0zfkjka5-harmonia-deps-3.3.0.drv
  /nix/store/kcznhz0y4364pk4ksm6zr27qgcs30jm7-harmonia-llvm-cov-3.3.0.drv