Fixed #23560 -- Fixed MigrationWrite to handle builtin types without imports.

Thanks Tim Graham for the review.

django/db/migrations/writer.py

@@ -352,7 +352,10 @@ class MigrationWriter(object):
                     return string, set(imports)
             if hasattr(value, "__module__"):
                 module = value.__module__
-                return "%s.%s" % (module, value.__name__), set(["import %s" % module])
+                if module == six.moves.builtins.__name__:
+                    return value.__name__, set()
+                else:
+                    return "%s.%s" % (module, value.__name__), set(["import %s" % module])
         # Other iterables
         elif isinstance(value, collections.Iterable):
             imports = set()

docs/releases/1.7.1.txt

@@ -83,3 +83,6 @@ Bugfixes
 * Coerced the ``related_name`` model field option to unicode during migration
   generation to generate migrations that work with both Python 2 and 3
   (:ticket:`23455`).
+
+* Fixed ``MigrationWriter`` to handle builtin types without imports
+  (:ticket:`23560`).

tests/migrations/test_writer.py

@@ -81,6 +81,11 @@ class WriterTests(TestCase):
         self.assertSerializedEqual(set([2, 3, "eighty"]))
         self.assertSerializedEqual({"lalalala": ["yeah", "no", "maybe"]})
         self.assertSerializedEqual(_('Hello'))
+        # Builtins
+        self.assertSerializedEqual([list, tuple, dict, set])
+        string, imports = MigrationWriter.serialize([list, tuple, dict, set])
+        self.assertEqual(string, "[list, tuple, dict, set]")
+        self.assertEqual(imports, set())
         # Functions
         with six.assertRaisesRegex(self, ValueError, 'Cannot serialize function: lambda'):
             self.assertSerializedEqual(lambda x: 42)