these 3 derivations will be built:
  /nix/store/ak6grplbivcf1ziz9klvhhgjnh5w1z4f-source.drv
  /nix/store/xqdvchcf4g0psp5mmmq83fqwcxq1jajv-harmonia-deps-3.2.0.drv
  /nix/store/qjpbhza8q3qkg0zbz8fmn1zssdjanrf3-harmonia-llvm-cov-3.2.0.drv