these 2 derivations will be built:
  /nix/store/9wpj3wav8xja5i7a54pdpz0zyxvcyk39-nix-source-patched-source.drv
  /nix/store/a7h3rrwhaabf33zhc4kr1shmjphyjcnz-equal-contents-trivial-patch-does-not-change-source-contents.drv