Removed join() promote kwarg

The join promote=True was over-aggressive in select_related handling.
After that was removed, the only other user was query.combine(). That
use case is very easy to handle locally, so there is no more need for
the join(promote=True) flag.

Refs #19849.

tests/regressiontests/select_related_regress/tests.py

@@ -139,3 +139,26 @@ class SelectRelatedRegressTests(TestCase):
         self.assertEqual(troy.name, 'Troy Buswell')
         self.assertEqual(troy.value, 42)
         self.assertEqual(troy.state.name, 'Western Australia')
+
+    def test_null_join_promotion(self):
+        australia = Country.objects.create(name='Australia')
+        active = ClientStatus.objects.create(name='active')
+
+        wa = State.objects.create(name="Western Australia", country=australia)
+        bob = Client.objects.create(name='Bob', status=active)
+        jack = Client.objects.create(name='Jack', status=active, state=wa)
+        qs = Client.objects.filter(state=wa).select_related('state')
+        with self.assertNumQueries(1):
+            self.assertEqual(list(qs), [jack])
+            self.assertEqual(qs[0].state, wa)
+            # The select_related join wasn't promoted as there was already an
+            # existing (even if trimmed) inner join to state.
+            self.assertFalse('LEFT OUTER' in str(qs.query))
+        qs = Client.objects.select_related('state').order_by('name')
+        with self.assertNumQueries(1):
+            self.assertEqual(list(qs), [bob, jack])
+            self.assertIs(qs[0].state, None)
+            self.assertEqual(qs[1].state, wa)
+            # The select_related join was promoted as there is already an
+            # existing join.
+            self.assertTrue('LEFT OUTER' in str(qs.query))