these 2 derivations will be built:
  /nix/store/757bvzrklb3n8hncd1sa3f5ml3v8hpbs-nix-source-patched-source.drv
  /nix/store/k9fa6xpwm1ddnbxf3b2hjjhvpnafdka2-equal-contents-trivial-patch-does-not-change-source-contents.drv