anchor.diff:  
     String getSelectedUri(UriBasedDirective node) {
       return LazyDirective.getSelectedUri(node);
  -  }
  -
  -  String getStringContent(LinkedNode node) {
  -    return node.simpleStringLiteral_value;
     }
   
     TypeName getSuperclass(AstNode node) {
  
positive.code:     throw UnimplementedError('${node.runtimeType}');
    }
  
    bool isMethod(LinkedNode node) {
      return node.kind == LinkedNodeKind.methodDeclaration;
    }
  
    bool isSetter(AstNode node) {
      if (node is FunctionDeclaration) {
        return node.isSetter;
  
negative.code:     throw StateError('Expected to find $indexInLibrary part directive.');
    }
  
    static NullabilitySuffix _nullabilitySuffix(EntityRefNullabilitySuffix data) {
      switch (data) {
        case EntityRefNullabilitySuffix.starOrIrrelevant:
  