anchor.diff:      hide AnalysisError, Element, ElementKind;
   import 'package:analyzer_plugin/src/utilities/change_builder/change_builder_dart.dart';
   import 'package:analyzer_plugin/src/utilities/string_utilities.dart';
  +import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
   import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
   import 'package:analyzer_plugin/utilities/fixes/fixes.dart' hide FixContributor;
   import 'package:analyzer_plugin/utilities/range_factory.dart';
  
positive.code:     if (newText == null) {
        return;
      }
      var changeBuilder = _newDartChangeBuilder();
      await changeBuilder.addFileEdit(pubspecFile.path,
          (DartFileEditBuilder builder) {
        builder.addSimpleReplacement(new SourceRange(offset, length), newText);
      });
      _addFixFromBuilder(changeBuilder, DartFixKind.UPDATE_SDK_CONSTRAINTS);
  
negative.code:     }
    }
  
    void _addFixFromBuilder(ChangeBuilder builder, FixKind kind,
        {List args: null, bool importsOnly: false}) {
      SourceChange change = builder.sourceChange;
      if (change.edits.isEmpty && !importsOnly) {
  