docs: def search_json_indexed_directory(directory):
          """Return a search function for searching a directory of packages, which has an index.json file
          created by the `mp install file` command.
  
          This will only search the issued index; it will not return results for the source index
          """
  
          from metapack.index import SearchIndex, search_index_file
  
          idx = SearchIndex(search_index_file())
  
          def _search_function(url):
  
              packages = idx.search(url, format='issued')
  
              if not packages:
                  return None
  
              package = packages.pop(0)
  
              try:
                  resource_str = '#' + url.target_file if url.fragment[0] else ''
  
                  return parse_app_url(package['url'] + resource_str, downloader=url.downloader)
              except KeyError as e:
                  return None
  
          return _search_function