anchor.diff:    final TypeEnvironmentStructure _environment;
     final TypeRecipe _recipe;
     final bool metadata;
  -  final bool hackTypeVariablesToAny;
   
     final List<FunctionTypeVariable> functionTypeVariables = [];
     final Set<TypeVariableType> typeVariables = {};
  
positive.code:   @override
    jsAst.Literal encodeGroundRecipe(ModularEmitter emitter, TypeRecipe recipe) {
      return _RecipeGenerator(this, emitter, null, recipe).run().recipe;
    }
  
    @override
    jsAst.Literal encodeRecipeWithVariablesReplaceByAny(
        ModularEmitter emitter, DartType dartType) {
      return _RecipeGenerator(this, emitter, null, TypeExpressionRecipe(dartType),
              hackTypeVariablesToAny: true)
          .run()
          .recipe;
    }
  
    @override
  
negative.code: 
    @override
    void visitTypeVariableType(TypeVariableType type, _) {
      TypeEnvironmentStructure environment = _environment;
      if (environment is SingletonTypeEnvironmentStructure) {
        if (type == environment.variable) {
  