anchor.diff:  
     inherit meta;
     passthru = { inherit url; } // passthru;
  -}
  +})
  
positive.code: , # Name of the file.  If empty, use the basename of `url' (or of the
    # first element of `urls').
    name ? ""
  
  , # SRI hash.
    hash ? ""
  
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;
  