function generateImportNames(ast: BabelNode): {
  importAll: string,
  importDefault: string,
} {
  let importDefault;
  let importAll;

  traverse(ast, {
    Program(path) {
      importAll = path.scope.generateUid('$$_IMPORT_ALL');
      importDefault = path.scope.generateUid('$$_IMPORT_DEFAULT');

      path.stop();
    },
  });

  return {
    importAll: nullthrows(importAll),
    importDefault: nullthrows(importDefault),
  };
}
Select unused names for "metroImportDefault" and "metroImportAll", by
calling "generateUid".