these 3 derivations will be built:
  /nix/store/g9ff30a5b6jcakaznbzqbsdqhss5g7yh-source.drv
  /nix/store/8d06v0pfd4h3r0a5nvlpz99rr8ar279c-harmonia-deps-3.2.0.drv
  /nix/store/fw9xk0yw9fjdbyh97rxlys0g88c1q0dc-harmonia-llvm-cov-3.2.0.drv