Fixed #27054 -- Fixed makemigrations crash with a read-only database.

tests/migrations/test_commands.py

@@ -12,7 +12,9 @@ from django.core.management import CommandError, call_command
 from django.db import (
     ConnectionHandler, DatabaseError, connection, connections, models,
 )
-from django.db.migrations.exceptions import InconsistentMigrationHistory
+from django.db.migrations.exceptions import (
+    InconsistentMigrationHistory, MigrationSchemaMissing,
+)
 from django.db.migrations.recorder import MigrationRecorder
 from django.test import ignore_warnings, mock, override_settings
 from django.utils import six
@@ -595,6 +597,27 @@ 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):
+        """
+        makemigrations ignores the non-default database if it's read-only.
+        """
+        def patched_ensure_schema(migration_recorder):
+            from django.db import connections
+            if migration_recorder.connection is connections['other']:
+                raise MigrationSchemaMissing()
+            else:
+                return mock.DEFAULT
+
+        self.assertTableNotExists('migrations_unicodemodel')
+        apps.register_model('migrations', UnicodeModel)
+        with mock.patch.object(
+                MigrationRecorder, 'ensure_schema',
+                autospec=True, side_effect=patched_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))
+
     def test_failing_migration(self):
         # If a migration fails to serialize, it shouldn't generate an empty file. #21280
         apps.register_model('migrations', UnserializableModel)