Fixed #25367 -- Allowed boolean expressions in QuerySet.filter() and exclude().

This allows using expressions that have an output_field that is a
BooleanField to be used directly in a queryset filters, or in the
When() clauses of a Case() expression.

Thanks Josh Smeaton, Tim Graham, Simon Charette, Mariusz Felisiak, and
Adam Johnson for reviews.

Co-Authored-By: NyanKiyoshi <hello@vanille.bid>

tests/expressions/tests.py

@@ -37,7 +37,7 @@ class BasicExpressionsTests(TestCase):
             ceo=Employee.objects.create(firstname="Joe", lastname="Smith", salary=10)
         )
         cls.foobar_ltd = Company.objects.create(
-            name="Foobar Ltd.", num_employees=3, num_chairs=4,
+            name="Foobar Ltd.", num_employees=3, num_chairs=4, based_in_eu=True,
             ceo=Employee.objects.create(firstname="Frank", lastname="Meyer", salary=20)
         )
         cls.max = Employee.objects.create(firstname='Max', lastname='Mustermann', salary=30)
@@ -83,6 +83,14 @@ class BasicExpressionsTests(TestCase):
             2,
         )
 
+    def test_filtering_on_q_that_is_boolean(self):
+        self.assertEqual(
+            Company.objects.filter(
+                ExpressionWrapper(Q(num_employees__gt=3), output_field=models.BooleanField())
+            ).count(),
+            2,
+        )
+
     def test_filter_inter_attribute(self):
         # We can filter on attribute relationships on same model obj, e.g.
         # find companies where the number of employees is greater
@@ -642,6 +650,56 @@ class BasicExpressionsTests(TestCase):
         with self.assertRaisesMessage(FieldError, "Cannot resolve keyword 'nope' into field."):
             list(Company.objects.filter(ceo__pk=F('point_of_contact__nope')))
 
+    def test_exists_in_filter(self):
+        inner = Company.objects.filter(ceo=OuterRef('pk')).values('pk')
+        qs1 = Employee.objects.filter(Exists(inner))
+        qs2 = Employee.objects.annotate(found=Exists(inner)).filter(found=True)
+        self.assertCountEqual(qs1, qs2)
+        self.assertFalse(Employee.objects.exclude(Exists(inner)).exists())
+        self.assertCountEqual(qs2, Employee.objects.exclude(~Exists(inner)))
+
+    def test_subquery_in_filter(self):
+        inner = Company.objects.filter(ceo=OuterRef('pk')).values('based_in_eu')
+        self.assertSequenceEqual(
+            Employee.objects.filter(Subquery(inner)),
+            [self.foobar_ltd.ceo],
+        )
+
+    def test_case_in_filter_if_boolean_output_field(self):
+        is_ceo = Company.objects.filter(ceo=OuterRef('pk'))
+        is_poc = Company.objects.filter(point_of_contact=OuterRef('pk'))
+        qs = Employee.objects.filter(
+            Case(
+                When(Exists(is_ceo), then=True),
+                When(Exists(is_poc), then=True),
+                default=False,
+                output_field=models.BooleanField(),
+            ),
+        )
+        self.assertSequenceEqual(qs, [self.example_inc.ceo, self.foobar_ltd.ceo, self.max])
+
+    def test_boolean_expression_combined(self):
+        is_ceo = Company.objects.filter(ceo=OuterRef('pk'))
+        is_poc = Company.objects.filter(point_of_contact=OuterRef('pk'))
+        self.gmbh.point_of_contact = self.max
+        self.gmbh.save()
+        self.assertSequenceEqual(
+            Employee.objects.filter(Exists(is_ceo) | Exists(is_poc)),
+            [self.example_inc.ceo, self.foobar_ltd.ceo, self.max],
+        )
+        self.assertSequenceEqual(
+            Employee.objects.filter(Exists(is_ceo) & Exists(is_poc)),
+            [self.max],
+        )
+        self.assertSequenceEqual(
+            Employee.objects.filter(Exists(is_ceo) & Q(salary__gte=30)),
+            [self.max],
+        )
+        self.assertSequenceEqual(
+            Employee.objects.filter(Exists(is_poc) | Q(salary__lt=15)),
+            [self.example_inc.ceo, self.max],
+        )
+
 
 class IterableLookupInnerExpressionsTests(TestCase):
     @classmethod