Fixed #37016 -- Avoided propagating invalid arguments from When() to Q().

Author: varunkasyap

django/db/models/expressions.py

@@ -12,7 +12,7 @@
 from django.db import DatabaseError, NotSupportedError, connection
 from django.db.models import fields
 from django.db.models.constants import LOOKUP_SEP
-from django.db.models.query_utils import Q
+from django.db.models.query_utils import PROHIBITED_FILTER_KWARGS, Q
 from django.utils.deconstruct import deconstructible
 from django.utils.functional import cached_property, classproperty
 from django.utils.hashable import make_hashable
@@ -1640,6 +1640,9 @@ class When(Expression):
 
     def __init__(self, condition=None, then=None, **lookups):
         if lookups:
+            if invalid_kwargs := PROHIBITED_FILTER_KWARGS.intersection(lookups):
+                invalid_str = ", ".join(f"'{k}'" for k in sorted(invalid_kwargs))
+                raise TypeError(f"The following kwargs are invalid: {invalid_str}")
             if condition is None:
                 condition, lookups = Q(**lookups), None
             elif getattr(condition, "conditional", False):

django/db/models/query.py

@@ -29,7 +29,7 @@
 from django.db.models.expressions import Case, DatabaseDefault, F, OrderBy, Value, When
 from django.db.models.fetch_modes import FETCH_ONE
 from django.db.models.functions import Cast, Trunc
-from django.db.models.query_utils import FilteredRelation, Q
+from django.db.models.query_utils import PROHIBITED_FILTER_KWARGS, FilteredRelation, Q
 from django.db.models.sql.constants import GET_ITERATOR_CHUNK_SIZE, ROW_COUNT
 from django.db.models.utils import (
     AltersData,
@@ -46,8 +46,6 @@
 # The maximum number of items to display in a QuerySet.__repr__
 REPR_OUTPUT_SIZE = 20
 
-PROHIBITED_FILTER_KWARGS = frozenset(["_connector", "_negated"])
-
 
 class BaseIterable:
     def __init__(

django/db/models/query_utils.py

@@ -21,6 +21,8 @@
 
 logger = logging.getLogger("django.db.models")
 
+PROHIBITED_FILTER_KWARGS = frozenset(["_connector", "_negated"])
+
 # PathInfo is used when converting lookups (fk__somecol). The contents
 # describe the relation in Model terms (model Options and Fields for both
 # sides of the relation. The join_field is the field backing the relation.

tests/expressions_case/tests.py

@@ -1668,6 +1668,11 @@ def test_invalid_when_constructor_args(self):
         with self.assertRaisesMessage(TypeError, msg):
             When()
 
+    def test_when_rejects_invalid_arguments(self):
+        msg = "The following kwargs are invalid: '_connector', '_negated'"
+        with self.assertRaisesMessage(TypeError, msg):
+            When(_negated=True, _connector="evil")
+
     def test_empty_q_object(self):
         msg = "An empty Q() can't be used as a When() condition."
         with self.assertRaisesMessage(ValueError, msg):