anchor.diff:  // Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
   // for details. All rights reserved. Use of this source code is governed by a
   // BSD-style license that can be found in the LICENSE file.
  -
  -import 'dart:collection';
   
   import 'package:analyzer/dart/analysis/features.dart';
   import 'package:analyzer/dart/ast/ast.dart';
  
positive.code:   }
  
    @override
    visitExpression(Expression e) {
      _assertLegacyType(e.staticType);
      _assertLegacyType(e.staticParameterElement?.type);
      super.visitExpression(e);
    }
  
    @override
  
negative.code: /// nodes, have legacy types, and asserts that the legacy types are deep legacy
  /// types.
  class LegacyTypeAsserter extends GeneralizingAstVisitor {
    Set<DartType> _visitedTypes = {};
  
    LegacyTypeAsserter({bool requireIsDebug = true}) {
      if (requireIsDebug) {
  