these 2 derivations will be built:
  /nix/store/6gjz0f64sd05jx8x1rciv1di15xl5a0g-lean-ctx-3.9.20-vendor.drv
  /nix/store/nx21zzjl90wv9zgzrh1r7bydlsj4yi70-lean-ctx-3.9.20.drv