Checklist

• I have verified that that issue exists against themaster branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to thediscussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to bein the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

classExampleSerializer(serializers.Serializer):a=serializers.CharField(required=True)b=serializers.CharField(required=False)classAnotherSerializer(serializers.Serializer):c=serializers.CharField(required=True)d=serializers.CharField(required=False)classExampleViewSet(ModelViewSet):serializer_class=ExampleSerializer@detail_route(methods=['post'],serializer_class=AnotherSerializer)defcustom_action(self,request,pk):returnsuper(ExampleSerializer,self).retrieve(self,request)

Expected behavior

Fieldsc andd fromAnotherSerializer in generated schema.

Actual behavior

Fieldsa andb fromExampleSerializer - serializer of viewset itself.