anchor.diff:  import 'dart:async';
   
  -import 'package:analyzer/dart/constant/value.dart';
   import 'package:analyzer/dart/element/element.dart';
   import 'package:analyzer/dart/element/visitor.dart';
   import 'package:build/build.dart';
  
positive.code: class DeepEqualityVisitor extends SimpleElementVisitor {
    static const deepEqualityKey = const _UniqueKey(
        'asset:compiled_mirrors/lib/compiled_mirrors.dart', 'CompileMirror');
    final classElementToPublicFields = <ClassElement, FieldElement>{};
  
    DeepEqualityVisitor();
  
  
negative.code:     var library = resolver.getLibrary(inputId);
      log.warning(
          'Investigating library ${library.exportNamespace.definedNames.keys}');
      var visitor = new DeepEqualityVisitor();
      library.visitChildren(visitor);
      if (visitor.descriptionGenerators.isNotEmpty) {
        // write output.
        var outStr = "import 'package:${inputId.package}/${inputId.path}';\n";
        for (var generator in visitor.descriptionGenerators) {
          outStr += '\n';
          outStr += generator.generatedCode;
        }
        log.warning(outStr);
        buildStep.writeAsString(outputId, outStr);
      }
    }
  
    @override
  