anchor.diff:      + ''
         chmod 755 "$out"
       '';
  -} // removeAttrs args [ "stripRoot" "extraPostFetch" ])).overrideAttrs (x: {
  +} // removeAttrs args [ "stripRoot" "extraPostFetch" "extension" ])).overrideAttrs (x: {
     # Hackety-hack: we actually need unzip hooks, too
     nativeBuildInputs = x.nativeBuildInputs ++ [ unzip ];
   })
  
positive.code:       mkdir "$unpackDir"
        cd "$unpackDir"
  
        renamed="$TMPDIR/${basename}"
        mv "$downloadedFile" "$renamed"
        unpackFile "$renamed"
      ''
  
negative.code: , urls ? []
  , extraPostFetch ? ""
  , name ? "source"
  , # Allows to set the extension for the intermediate downloaded
    # file. This can be used as a hint for the unpackCmdHooks to select
    # an appropriate unpacking tool.
    extension ? null
  , ... } @ args:
  
  (fetchurl (let
    tmpFilename =
      if extension != null
      then "download.${extension}"
      else baseNameOf (if url != "" then url else builtins.head urls);
  in {
    inherit name;
  
  