SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "async_foo"
    PARAM_LIST
      L_PAREN "("
      PARAM
        WILDCARD_PAT
          UNDERSCORE "_"
        COLON ":"
        WHITESPACE " "
        IMPL_TRAIT_TYPE
          IMPL_KW "impl"
          WHITESPACE " "
          TYPE_BOUND_LIST
            TYPE_BOUND
              ASYNC_KW "async"
              WHITESPACE " "
              PATH_TYPE
                PATH
                  PATH_SEGMENT
                    NAME_REF
                      IDENT "Fn"
                    PARENTHESIZED_ARG_LIST
                      L_PAREN "("
                      TYPE_ARG
                        REF_TYPE
                          AMP "&"
                          PATH_TYPE
                            PATH
                              PATH_SEGMENT
                                NAME_REF
                                  IDENT "i32"
                      R_PAREN ")"
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        R_CURLY "}"
  WHITESPACE "\n"
