these 2 derivations will be built:
  /nix/store/g1p2ndy7d1dp3qabrr03j5vsfjkg474m-nix-source-patched-source.drv
  /nix/store/i0dv1h2riim92i40ajx4yina95yv4yis-equal-contents-trivial-patch-does-not-change-source-contents.drv