anchor.diff:    NormalNamer(this.prefix);
   }
   
  +class FakePrintingConstant extends Constant {
  +  final String id;
  +  FakePrintingConstant(this.id);
  +
  +  @override
  +  accept(ConstantVisitor v) {}
  +
  +  @override
  +  acceptReference(Visitor v) {}
  +
  +  @override
  +  DartType getType(TypeEnvironment types) => null;
  +
  +  @override
  +  void visitChildren(Visitor v) {}
  +
  +  @override
  +  String toString() {
  +    return "FakePrintingConstant[$id]";
  +  }
  +}
  +
   class ConstantNamer extends RecursiveVisitor<Null> with Namer<Constant> {
     final String prefix;
     ConstantNamer(this.prefix);
   
     String getName(Constant constant) {
  -    if (!map.containsKey(constant)) {
  -      // Name everything in post-order visit of DAG.
  -      constant.visitChildren(this);
  -    }
  -    return super.getName(constant);
  +    try {
  +      if (!map.containsKey(constant)) {
  +        // Name everything in post-order visit of DAG.
  +        constant.visitChildren(this);
  +      }
  +      return super.getName(constant);
  +    } catch (e) {
  +      // Partial dill. Name anyway.
  +      String id = "${constant.runtimeType.toString()}";
  +      return super.getName(new FakePrintingConstant(id));
  +    }
     }
   
     defaultConstantReference(Constant constant) {
  
positive.code:     writeConstantReference(node);
      writeSpaced('=');
      writeClassReferenceFromReference(node.classReference);
      if (!node.classNode.typeParameters.isEmpty) {
        writeSymbol('<');
        writeList(node.typeArguments, writeType);
        writeSymbol('>');
      }
      writeSymbol(' {');
      writeList(node.fieldValues.entries, (entry) {
        writeWord('${entry.key.asField.name.name}');
        writeSymbol(':');
        writeConstantReference(entry.value);
      });
  
negative.code: library kernel.ast_to_text;
  
  import 'dart:core' hide MapEntry;
  import 'dart:core' as core show MapEntry;
  
  import 'dart:convert' show json;
  
  import 'package:kernel/type_environment.dart' show TypeEnvironment;
  
  import '../ast.dart';
  import '../import_table.dart';
  