these 3 derivations will be built:
  /nix/store/1hxqw5qccxvavaj8dgxr9m5kgvs5nmq2-source.drv
  /nix/store/zz5mlyrgf4z729am8kky7qgf8ncfjii2-harmonia-deps-3.2.0.drv
  /nix/store/mwmam7v2k0a1hsxc3psvk2qmg91hsx1v-harmonia-llvm-cov-3.2.0.drv