anchor.diff:  
     @override
     void visitExtensionDeclaration(ExtensionDeclaration node) {
  -    if (!isInLibFolder) return;
  -
       if (node.name == null || isPrivate(node.name)) {
         return;
       }
  
positive.code:   @override
    void registerNodeProcessors(
        NodeLintRegistry registry, LinterContext context) {
      final visitor = _Visitor(this, context);
      registry.addClassDeclaration(this, visitor);
      registry.addClassTypeAlias(this, visitor);
  
negative.code:   }
  
    void _visitClassOrMixin(ClassOrMixinDeclaration node) {
      if (isPrivate(node.name)) return;
  
      check(node);
  