these 3 derivations will be built:
  /nix/store/9624vjplwf2c1dr95sz0h9n41n750m6x-source.drv
  /nix/store/02cln2gj0a61bc0a3zmf5a7g5iab3pmp-harmonia-deps-3.1.0.drv
  /nix/store/r8vbix8cfg35avqx5i8qbs7s6h0fy043-harmonia-llvm-cov-3.1.0.drv