[1.9.x] Fixed #25922 -- Fixed migrate --fake-initial detection of many-to-many tables.

Backport of fa9ce4e9a6 from master

tests/migrations/test_executor.py

@@ -301,6 +301,65 @@ class ExecutorTests(MigrationTestBase):
         self.assertTableNotExists("migrations_author")
         self.assertTableNotExists("migrations_tribble")
 
+    @override_settings(
+        MIGRATION_MODULES={
+            "migrations": "migrations.test_add_many_to_many_field_initial",
+        },
+    )
+    def test_detect_soft_applied_add_field_manytomanyfield(self):
+        """
+        executor.detect_soft_applied() detects ManyToManyField tables from an
+        AddField operation. This checks the case of AddField in a migration
+        with other operations (0001) and the case of AddField in its own
+        migration (0002).
+        """
+        tables = [
+            # from 0001
+            "migrations_project",
+            "migrations_task",
+            "migrations_project_tasks",
+            # from 0002
+            "migrations_task_projects",
+        ]
+        executor = MigrationExecutor(connection)
+        # Create the tables for 0001 but make it look like the migration hasn't
+        # been applied.
+        executor.migrate([("migrations", "0001_initial")])
+        executor.migrate([("migrations", None)], fake=True)
+        for table in tables[:3]:
+            self.assertTableExists(table)
+        # Table detection sees 0001 is applied but not 0002.
+        migration = executor.loader.get_migration("migrations", "0001_initial")
+        self.assertEqual(executor.detect_soft_applied(None, migration)[0], True)
+        migration = executor.loader.get_migration("migrations", "0002_initial")
+        self.assertEqual(executor.detect_soft_applied(None, migration)[0], False)
+
+        # Create the tables for both migrations but make it look like neither
+        # has been applied.
+        executor.loader.build_graph()
+        executor.migrate([("migrations", "0001_initial")], fake=True)
+        executor.migrate([("migrations", "0002_initial")])
+        executor.loader.build_graph()
+        executor.migrate([("migrations", None)], fake=True)
+        # Table detection sees 0002 is applied.
+        migration = executor.loader.get_migration("migrations", "0002_initial")
+        self.assertEqual(executor.detect_soft_applied(None, migration)[0], True)
+
+        # Leave the tables for 0001 except the many-to-many table. That missing
+        # table should cause detect_soft_applied() to return False.
+        with connection.schema_editor() as editor:
+            for table in tables[2:]:
+                editor.execute(editor.sql_delete_table % {"table": table})
+        migration = executor.loader.get_migration("migrations", "0001_initial")
+        self.assertEqual(executor.detect_soft_applied(None, migration)[0], False)
+
+        # Cleanup by removing the remaining tables.
+        with connection.schema_editor() as editor:
+            for table in tables[:2]:
+                editor.execute(editor.sql_delete_table % {"table": table})
+        for table in tables:
+            self.assertTableNotExists(table)
+
     @override_settings(
         INSTALLED_APPS=[
             "migrations.migrations_test_apps.lookuperror_a",