python/hooks: restore catchConflictHook for python<3.10

import pkg_resources

import collections

import sys

do_abort = False

packages = collections.defaultdict(list)

for f in sys.path:

    for req in pkg_resources.find_distributions(f):

        if req not in packages[req.project_name]:

            # some exceptions inside buildPythonPackage

            if req.project_name in ['setuptools', 'pip', 'wheel']:

                continue

            packages[req.project_name].append(req)

for name, duplicates in packages.items():

    if len(duplicates) > 1:

        do_abort = True

        print("Found duplicated packages in closure for dependency '{}': ".format(name))

        for dup in duplicates:

            print("  " + repr(dup))

if do_abort:

    print("")

    print(

        'Package duplicates found in closure, see above. Usually this '

        'happens if two packages depend on different version '

        'of the same dependency.')

    sys.exit(1)

  pythonCatchConflictsHook = callPackage ({ makePythonHook, setuptools }:

    makePythonHook {

      name = "python-catch-conflicts-hook";

      substitutions = {

      substitutions = let

        useLegacyHook = lib.versionOlder python.version "3.10";

      in {

        inherit pythonInterpreter pythonSitePackages;

        catchConflicts=../catch_conflicts/catch_conflicts.py;

        catchConflicts = if useLegacyHook then

          ../catch_conflicts/catch_conflicts_py2.py

        else

          ../catch_conflicts/catch_conflicts.py;

      } // lib.optionalAttrs useLegacyHook {

        inherit setuptools;

      };

    } ./python-catch-conflicts-hook.sh) {};