code: def parse_directive(lexer: Lexer, is_const: bool) -> DirectiveNode:
      
      start = lexer.token
      expect_token(lexer, TokenKind.AT)
      return DirectiveNode(
          name=parse_name(lexer),
          arguments=parse_arguments(lexer, is_const),
          loc=loc(lexer, start),
      )
docs: Directive[Const]: @ Name Arguments[?Const]?