anchor.diff:        # Tar up the layer and throw it into 'layer.tar'.
         echo "Packing layer..."
         mkdir $out
  -      tar -C layer --mtime=0 -cf $out/layer.tar .
  +      tar -C layer --mtime="@$SOURCE_DATE_EPOCH" -cf $out/layer.tar .
   
         # Compute a checksum of the tarball.
         echo "Computing layer checksum..."
  
positive.code: 
          echo "Packing layer..."
          mkdir $out
          tar -C layer --mtime=0 -cf $out/layer.tar .
  
          # Compute the tar checksum and add it to the output json.
          echo "Computing checksum..."
  
negative.code:         echo "Adding contents..."
          for item in ${toString contents}; do
            echo "Adding $item..."
            rsync -ak --chown=0:0 $item/ layer/
          done
        '';
  
  