these 4 derivations will be built:
  /nix/store/cp1wbcaxzyi9xxnmvj3s8vc6fra3yvhm-Cargo.toml.drv
  /nix/store/xfwmpyr8xs5g9s0abws8x08lrm6sfkw7-source.drv
  /nix/store/k4439kv2jc25cw4ypmgdcmwmxpz2rdj8-harmonia-deps-3.3.0.drv
  /nix/store/icw9m5k47jf9qycbb8w2p6rs7vq81826-harmonia-llvm-cov-3.3.0.drv