these 3 derivations will be built:
  /nix/store/44nvg5hi82ja9s8bdcfffb8nqkvlncdz-source.drv
  /nix/store/5k6hb3jsfww7mgg78gr635671l27lv6z-harmonia-deps-3.2.0.drv
  /nix/store/0h1jkswz0bs4msbvnw7av880bkiy77yx-harmonia-llvm-cov-3.2.0.drv