these 2 derivations will be built:
  /nix/store/x4n3q03vi6d4y4fb6jwwv9ajpb4z74v8-nix-source-patched-source.drv
  /nix/store/v71ajpxp51b5chdf0pygyisj2x54h90g-equal-contents-trivial-patch-does-not-change-source-contents.drv