anchor.diff:            name: fieldInfo.name, parent: parentNode, type: vm.NodeType.other);
         newField.size = fieldInfo.size;
         parentNode.children[newField.name] = newField;
  +      vm.ProgramInfoNode? fieldNode = infoNodesByName[newField.name];
  +      assert(fieldNode == null, "encountered field with duplicated name");
         infoNodesByName[newField.name] = newField;
         outputInfo.add(newField);
       }
  
positive.code:         name: libraryName, parent: parentNode, type: vm.NodeType.libraryNode);
      newLibrary.size = libraryInfo.size;
      parentNode.children[newLibrary.name] = newLibrary;
      infoNodesByName[newLibrary.name] = newLibrary;
      outputInfo.add(newLibrary);
    }
  
negative.code:           parent: parentNode,
            type: vm.NodeType.other);
        newClassType.size = classTypeInfo.size;
        vm.ProgramInfoNode? classTypeNode = infoNodesByName[newClassType.name];
        assert(
            classTypeNode == null, "encountered classType with duplicated name");
        infoNodesByName[newClassType.name] = newClassType;
        outputInfo.add(newClassType);
      }
  