==================
Immediately-invoked block closure (IIFE) is a function_expression callee
==================

void main() {
  var x = (){ return 1; }();
}

---

(program
  (function_signature
    (void_type)
    (identifier)
    (formal_parameter_list))
  (function_body
    (block
      (local_variable_declaration
        (initialized_variable_definition
          (inferred_type)
          (identifier)
          (function_expression
            (formal_parameter_list)
            (function_expression_body
              (block
                (return_statement
                  (decimal_integer_literal)))))
          (selector
            (argument_part
              (arguments))))))))
