Fixed #30657 -- Allowed customizing Field's descriptors with a descriptor_class attribute.

Allows model fields to override the descriptor class used on the model
instance attribute.

tests/field_subclassing/fields.py

@@ -1,6 +1,26 @@
 from django.db import models
+from django.db.models.query_utils import DeferredAttribute
 
 
 class CustomTypedField(models.TextField):
     def db_type(self, connection):
         return 'custom_field'
+
+
+class CustomDeferredAttribute(DeferredAttribute):
+    def __get__(self, instance, cls=None):
+        self._count_call(instance, 'get')
+        return super().__get__(instance, cls)
+
+    def __set__(self, instance, value):
+        self._count_call(instance, 'set')
+        instance.__dict__[self.field.attname] = value
+
+    def _count_call(self, instance, get_or_set):
+        count_attr = '_%s_%s_count' % (self.field.attname, get_or_set)
+        count = getattr(instance, count_attr, 0)
+        setattr(instance, count_attr, count + 1)
+
+
+class CustomDescriptorField(models.CharField):
+    descriptor_class = CustomDeferredAttribute