code: private function parseConstArgument()
      {
          $start = $this->lexer->token;
          $name  = $this->parseName();
  
          $this->expect(Token::COLON);
          $value = $this->parseConstValue();
  
          return new ArgumentNode([
              'name'  => $name,
              'value' => $value,
              'loc'   => $this->loc($start),
          ]);
      }
docs: @return ArgumentNode
  
  @throws SyntaxError