docs: def walk_revctrl(dirname='', ff=''):
      """Return files found by the file-finder 'ff'.
      """
      file_finder = None
      items = []
  
      if not ff:
          distutils.log.error('No file-finder passed to walk_revctrl')
          sys.exit(1)
  
      for ep in pkg_resources.iter_entry_points('setuptools.file_finders'):
          if ff == ep.name:
              distutils.log.info('using %s file-finder', ep.name)
              file_finder = ep.load()
              finder_items = []
              with pythonpath_off():
                  for item in file_finder(dirname):
                      if not basename(item).startswith(('.svn', '.hg', '.git')):
                          finder_items.append(item)
              distutils.log.info('%d files found', len(finder_items))
              items.extend(finder_items)
  
      if file_finder is None:
          distutils.log.error('Failed to load %s file-finder; setuptools-%s extension missing?',
              ff, 'subversion' if ff == 'svn' else ff)
          sys.exit(1)
  
      # Returning a non-empty list prevents egg_info from reading the
      # existing SOURCES.txt
      return items or ['']