anchor.diff:    /// The token for the 'external' keyword, or `null` if the constructor is not
     /// external.
     @override
  -  Token? externalKeyword;
  +  final Token? externalKeyword;
   
     /// The token for the 'const' keyword, or `null` if the constructor is not a
     /// const constructor.
  
positive.code: class ReturnStatementImpl extends StatementImpl implements ReturnStatement {
    /// The token representing the 'return' keyword.
    @override
    Token returnKeyword;
  
    /// The expression computing the value to be returned, or `null` if no
    /// explicit value was provided.
  
negative.code: abstract class ForEachPartsImpl extends ForLoopPartsImpl
      implements ForEachParts {
    @override
    final Token inKeyword;
  
    /// The expression evaluated to produce the iterator.
    ExpressionImpl _iterable;
  