anchor.diff:          // Check and schedule the latest stable version of each package.
           final Query packageQuery = _db.query(Package)..order('-updated');
           await for (Package p in packageQuery.run()) {
  -          if (await _requiresUpdate(p.name, p.latestVersion)) {
  +          if (await _requiresUpdate(p.name, p.latestVersion,
  +              retryFailed: true)) {
               yield new Task(p.name, p.latestVersion, p.updated);
             }
   
  
positive.code:     }
    }
  
    Future<bool> _requiresUpdate(
        String packageName, String packageVersion) async {
      final List<PackageVersionAnalysis> list = await _db.lookup([
        _db.emptyKey
            .append(PackageAnalysis, id: packageName)
  
negative.code: import 'package:logging/logging.dart';
  
  import '../frontend/models.dart';
  import '../shared/analyzer_service.dart' show AnalysisStatus;
  import '../shared/task_scheduler.dart';
  import '../shared/task_sources.dart';
  import '../shared/utils.dart';
  