these 2 derivations will be built:
  /nix/store/16zdb8pnjrcidzh5ypng5rgqa3q6i20l-nix-source-patched-source.drv
  /nix/store/xv5rhdyd88sk0hymj850iyrs9npnz3a0-equal-contents-trivial-patch-does-not-change-source-contents.drv