anchor.diff:  
     @override
     void visitTypeVariableType(TypeVariableType type, _) {
  -    if (hackTypeVariablesToAny) {
  -      // Emit 'any' type.
  -      _emitExtensionOp(Recipe.pushAnyExtension);
  -      return;
  -    }
  -
       TypeEnvironmentStructure environment = _environment;
       if (environment is SingletonTypeEnvironmentStructure) {
         if (type == environment.variable) {
  
positive.code: 
    _RecipeGenerator(
        this._encoder, this._emitter, this._environment, this._recipe,
        {this.metadata = false, this.hackTypeVariablesToAny = false});
  
    JClosedWorld get _closedWorld => _encoder._closedWorld;
    NativeBasicData get _nativeData => _encoder._nativeData;
  
negative.code:   final TypeEnvironmentStructure _environment;
    final TypeRecipe _recipe;
    final bool metadata;
  
    final List<FunctionTypeVariable> functionTypeVariables = [];
    final Set<TypeVariableType> typeVariables = {};
  