these 4 derivations will be built:
  /nix/store/740465pji8glkglw9x5s449wsipv1qd0-Cargo.toml.drv
  /nix/store/xxirs8i6q7mx1n3mnia59rm29pv7m973-source.drv
  /nix/store/1989abb1qnzmpfx4cdc4w94rndmjvn6y-harmonia-deps-3.2.0.drv
  /nix/store/g52mq3fcd5jqr46y2z4m0pyydb7pgby1-harmonia-llvm-cov-3.2.0.drv