Fixed #27142, #27110 -- Made makemigrations consistency checks respect database routers.

Partially reverted refs #27054 except for one of the tests as this
solution supersedes that one.

Thanks Shai Berger for the review.

tests/migrations/test_commands.py

@@ -22,6 +22,7 @@ from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import force_text
 
 from .models import UnicodeModel, UnserializableModel
+from .routers import TestRouter
 from .test_base import MigrationTestBase
 
 
@@ -597,14 +598,14 @@ class MakeMigrationsTests(MigrationTestBase):
                 init_file = os.path.join(migration_dir, '__init__.py')
                 self.assertTrue(os.path.exists(init_file))
 
-    def test_makemigrations_other_datbase_is_readonly(self):
+    def test_makemigrations_consistency_checks_respect_routers(self):
         """
-        makemigrations ignores the non-default database if it's read-only.
+        The history consistency checks in makemigrations respect
+        settings.DATABASE_ROUTERS.
         """
         def patched_ensure_schema(migration_recorder):
-            from django.db import connections
             if migration_recorder.connection is connections['other']:
-                raise MigrationSchemaMissing()
+                raise MigrationSchemaMissing('Patched')
             else:
                 return mock.DEFAULT
 
@@ -612,11 +613,33 @@ class MakeMigrationsTests(MigrationTestBase):
         apps.register_model('migrations', UnicodeModel)
         with mock.patch.object(
                 MigrationRecorder, 'ensure_schema',
-                autospec=True, side_effect=patched_ensure_schema):
+                autospec=True, side_effect=patched_ensure_schema) as ensure_schema:
             with self.temporary_migration_module() as migration_dir:
                 call_command("makemigrations", "migrations", verbosity=0)
                 initial_file = os.path.join(migration_dir, "0001_initial.py")
                 self.assertTrue(os.path.exists(initial_file))
+                self.assertEqual(ensure_schema.call_count, 1)  # 'default' is checked
+
+                # Router says not to migrate 'other' so consistency shouldn't
+                # be checked.
+                with self.settings(DATABASE_ROUTERS=['migrations.routers.TestRouter']):
+                    call_command('makemigrations', 'migrations', verbosity=0)
+                self.assertEqual(ensure_schema.call_count, 2)  # 'default' again
+
+                # With a router that doesn't prohibit migrating 'other',
+                # consistency is checked.
+                with self.settings(DATABASE_ROUTERS=['migrations.routers.EmptyRouter']):
+                    with self.assertRaisesMessage(MigrationSchemaMissing, 'Patched'):
+                        call_command('makemigrations', 'migrations', verbosity=0)
+                self.assertEqual(ensure_schema.call_count, 4)  # 'default' and 'other'
+
+                # With a router that doesn't allow migrating on any database,
+                # no consistency checks are made.
+                with self.settings(DATABASE_ROUTERS=['migrations.routers.TestRouter']):
+                    with mock.patch.object(TestRouter, 'allow_migrate', return_value=False) as allow_migrate:
+                        call_command('makemigrations', 'migrations', verbosity=0)
+                allow_migrate.assert_called_with('other', 'migrations')
+                self.assertEqual(ensure_schema.call_count, 4)
 
     def test_failing_migration(self):
         # If a migration fails to serialize, it shouldn't generate an empty file. #21280