anchor.diff:    /// [ClassElement] is analogous to [InheritingContainer].
     ClassElement get element => super.element;
   
  -  // TODO(srawlins): To make final, remove public getter, setter, rename to be
  -  // public, and add `final` modifier.
  -  DefinedElementType _supertype;
  -  DefinedElementType get supertype => _supertype;
  -
  -  @Deprecated('Field intended to be final; setter will be removed as early as '
  -      'Dartdoc 1.0.0')
  -  set supertype(DefinedElementType value) => _supertype = value;
  +  final DefinedElementType supertype;
   
     InheritingContainer(
         ClassElement element, Library library, PackageGraph packageGraph)
  -      : _supertype = element.supertype?.element?.supertype == null
  +      : supertype = element.supertype?.element?.supertype == null
               ? null
               : ElementType.from(element.supertype, library, packageGraph),
           super(element, library, packageGraph);
  
positive.code: // 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.
  
  
negative.code: 
    List<TypeParameter> _typeParameters;
  
    @override
    List<TypeParameter> get typeParameters {
      _typeParameters ??= element.typeParameters.map((f) {
  