anchor.diff:        return new ListExpression(expressions, ListSeparator.comma,
             span: scanner.spanFrom(start));
       } finally {
  -      _inParentheses = false;
  +      _inParentheses = wasInParentheses;
       }
     }
   
  
positive.code:     }
      scanner.expectChar($rparen);
  
      return new ArgumentInvocation(positional, named, scanner.spanFrom(start),
          rest: rest, keywordRest: keywordRest);
    }
  
negative.code: 
    /// Consumes a parenthesized expression.
    Expression _parentheses() {
      var wasInParentheses = _inParentheses;
      _inParentheses = true;
      try {
        var start = scanner.state;
        scanner.expectChar($lparen);
        whitespace();
  