these 4 derivations will be built:
  /nix/store/4dp0hrhg08c758l6z4gim99n8k6cy1fb-Cargo.toml.drv
  /nix/store/ckbwr5ngj167hbhkmpvdyx0kgicqn8mi-source.drv
  /nix/store/yjsiaiy0c6bjpp4xclvr1pk5yjqcpzs4-harmonia-deps-3.3.0.drv
  /nix/store/nj371gip3x8nw2b6nk7hjvb9agg5s1xn-harmonia-llvm-cov-3.3.0.drv