code: function augmentConfigExtended(
    stylelint /*: stylelint$internalApi*/,
    cosmiconfigResultArg /*: ?{
       config: stylelint$config,
       filepath: string,
     }*/
  ) /*: Promise<?{ config: stylelint$config, filepath: string }>*/ {
    const cosmiconfigResult = cosmiconfigResultArg; // Lock in for Flow
  
    if (!cosmiconfigResult) return Promise.resolve(null);
  
    const configDir = path.dirname(cosmiconfigResult.filepath || "");
    const cleanedConfig = _.omit(cosmiconfigResult.config, "ignoreFiles");
  
    return augmentConfigBasic(stylelint, cleanedConfig, configDir).then(
      augmentedConfig => {
        return {
          config: augmentedConfig,
          filepath: cosmiconfigResult.filepath
        };
      }
    );
  }
docs: Extended configs need to be run through augmentConfigBasic but do not need the full treatment. Things like pluginFunctions will be resolved and added by the parent config.