these 3 derivations will be built:
  /nix/store/i1hh91jp23i0x3qw9wwpgmai5i9ia257-source.drv
  /nix/store/zswd4cn22x5xdb1ip2dxbfd65icdq2wg-harmonia-deps-3.3.0.drv
  /nix/store/9ik366lxnia1a0idd16l72w0nfv31r1q-harmonia-llvm-cov-3.3.0.drv