anchor.diff:    void _preVisit(AssignedVariables<Node, Var> assignedVariables) {}
   
     @override
  -  Type _visit(Harness h) {
  +  Type _visit(Harness h, Type context) {
       return h._typeAnalyzer.analyzeThis(this);
     }
   }
  
positive.code:   late final Type neverType = Type('Never');
  
    late final Type nullType = Type('Null');
  
    _MiniAstTypeAnalyzer(this._harness);
  
  
negative.code:   }
  
    @override
    Type _visit(Harness h, Type context) {
      var type = h._typeAnalyzer.analyzeExpression(target);
      h._flow.forwardExpression(this, target);
      Type.withComparisonsAllowed(() {
  