anchor.diff:  { stdenv, buildPythonPackage, fetchFromGitHub, pythonOlder, isPy27
  -, backports_functools_lru_cache, configparser, futures, future, jedi, pluggy, python-jsonrpc-server
  +, backports_functools_lru_cache, configparser, futures, future, jedi, pluggy, python-jsonrpc-server, flake8
   , pytest, mock, pytestcov, coverage, setuptools
   , # Allow building a limited set of providers, e.g. ["pycodestyle"].
     providers ? ["*"]
  
positive.code: 
  buildPythonPackage rec {
    pname = "python-language-server";
    version = "0.28.3";
  
    src = fetchFromGitHub {
      owner = "palantir";
      repo = "python-language-server";
      rev = version;
      sha256 = "16d8i43r75h0cijggkkmmpnycn29wlbjp63mgg3s4nbrxfa96x2k";
    };
  
    # The tests require all the providers, disable otherwise.
  
negative.code:     HOME=$TEMPDIR pytest
    '';
  
    propagatedBuildInputs = [ setuptools jedi pluggy future python-jsonrpc-server flake8 ]
      ++ stdenv.lib.optional (withProvider "autopep8") autopep8
      ++ stdenv.lib.optional (withProvider "mccabe") mccabe
      ++ stdenv.lib.optional (withProvider "pycodestyle") pycodestyle
  