Refs #25550 -- Removed support for direct assignment to the reverse side of a related set.

django/db/models/fields/related_descriptors.py

@@ -510,28 +510,16 @@ class ReverseManyToOneDescriptor(object):
         return self.related_manager_cls(instance)
 
     def _get_set_deprecation_msg_params(self):
-        return (  # RemovedInDjango20Warning
+        return (
             'reverse side of a related set',
             self.rel.get_accessor_name(),
         )
 
     def __set__(self, instance, value):
-        """
-        Set the related objects through the reverse relation.
-
-        With the example above, when setting ``parent.children = children``:
-
-        - ``self`` is the descriptor managing the ``children`` attribute
-        - ``instance`` is the ``parent`` instance
-        - ``value`` is the ``children`` sequence on the right of the equal sign
-        """
-        warnings.warn(
-            'Direct assignment to the %s is deprecated due to the implicit '
-            'save() that happens. Use %s.set() instead.' % self._get_set_deprecation_msg_params(),
-            RemovedInDjango20Warning, stacklevel=2,
+        raise TypeError(
+            'Direct assignment to the %s is prohibited. Use %s.set() instead.'
+            % self._get_set_deprecation_msg_params(),
         )
-        manager = self.__get__(instance)
-        manager.set(value)
 
 
 def create_reverse_many_to_one_manager(superclass, rel):
@@ -772,7 +760,7 @@ class ManyToManyDescriptor(ReverseManyToOneDescriptor):
         )
 
     def _get_set_deprecation_msg_params(self):
-        return (  # RemovedInDjango20Warning
+        return (
             '%s side of a many-to-many set' % ('reverse' if self.reverse else 'forward'),
             self.rel.get_accessor_name() if self.reverse else self.field.name,
         )