anchor.diff:  , # Name of the file.  If empty, use the basename of `url' (or of the
     # first element of `urls').
     name ? ""
  +
  +  # for versioned downloads optionally take pname + version.
  +  # if name is set that is preferred
  +, pname ? ""
  +, version ? ""
   
   , # SRI hash.
     hash ? ""
  
positive.code: 
    inherit meta;
    passthru = { inherit url; } // passthru;
  }
  
negative.code:     else throw "fetchurl requires a hash for fixed-output derivation: ${lib.concatStringsSep ", " urls_}";
  in
  
  stdenvNoCC.mkDerivation ((
    if (pname != "" && version != "") then
      { inherit pname version; }
    else
      { name =
        if showURLs then "urls"
        else if name != "" then name
        else baseNameOf (toString (builtins.head urls_));
      }
  ) // {
    builder = ./builder.sh;
  
    nativeBuildInputs = [ curl ] ++ nativeBuildInputs;
  