these 3 derivations will be built:
  /nix/store/yhhwq7ld926vv05mnf5kilbxk7v570n4-source.drv
  /nix/store/nw5fnlsrfx7wwrsyq8r3q14l3vfh1rhw-harmonia-deps-3.3.0.drv
  /nix/store/zryp1g4rnfqm012pgya0y9wzviik98yz-harmonia-llvm-cov-3.3.0.drv