Fixed #29897 -- Fixed autodetector's swappable MTI dependency resolution.

Thanks Steven Ganz for the detailed report.

django/db/migrations/autodetector.py

@@ -345,6 +345,9 @@ class MigrationAutodetector:
             dependency_graph = {op: set() for op in ops}
             for op in ops:
                 for dep in op._auto_deps:
+                    # Resolve intra-app dependencies to handle circular
+                    # references involving a swappable model.
+                    dep = self._resolve_dependency(dep)[0]
                     if dep[0] == app_label:
                         for op2 in ops:
                             if self.check_dependency(op2, dep):

tests/migrations/test_autodetector.py

@@ -2348,6 +2348,18 @@ class AutodetectorTests(TestCase):
         self.assertOperationTypes(changes, 'a', 0, ["CreateModel"])
         self.assertMigrationDependencies(changes, 'a', 0, [])
 
+    @override_settings(AUTH_USER_MODEL='a.User')
+    def test_swappable_circular_multi_mti(self):
+        with isolate_lru_cache(apps.get_swappable_settings_name):
+            parent = ModelState('a', 'Parent', [
+                ('user', models.ForeignKey(settings.AUTH_USER_MODEL, models.CASCADE))
+            ])
+            child = ModelState('a', 'Child', [], bases=('a.Parent',))
+            user = ModelState('a', 'User', [], bases=(AbstractBaseUser, 'a.Child'))
+            changes = self.get_changes([], [parent, child, user])
+        self.assertNumberMigrations(changes, 'a', 1)
+        self.assertOperationTypes(changes, 'a', 0, ['CreateModel', 'CreateModel', 'CreateModel', 'AddField'])
+
     @mock.patch('django.db.migrations.questioner.MigrationQuestioner.ask_not_null_addition',
                 side_effect=AssertionError("Should not have prompted for not null addition"))
     def test_add_blank_textfield_and_charfield(self, mocked_ask_method):