these 4 derivations will be built:
  /nix/store/fad1va26ld56zav98s3xxrvpvlyrl0nj-Cargo.toml.drv
  /nix/store/hg7vamkgzcyjiqyps88sxx9k7sj3cxwf-source.drv
  /nix/store/nnm2c9mpkfjhnc1mpj3484zw5ad5hyzx-harmonia-deps-3.3.0.drv
  /nix/store/v5qlihvsvzicnblr44adqfkd8w07b59y-harmonia-llvm-cov-3.3.0.drv