Fixed #19401 -- Ensure that swappable model references are case insensitive.

This is necessary because get_model() checks are case insensitive, and if the swapable check isn't, the
swappable logic gets tied up in knots with models that are partially swapped out.

Thanks to chris@cogdon.org for the report and extensive analysis, and Preston for his work on the draft patch.

django/db/models/options.py

@@ -213,11 +213,24 @@ class Options(object):
         """
         Has this model been swapped out for another? If so, return the model
         name of the replacement; otherwise, return None.
+
+        For historical reasons, model name lookups using get_model() are
+        case insensitive, so we make sure we are case insensitive here.
         """
         if self.swappable:
-            model_label = '%s.%s' % (self.app_label, self.object_name)
+            model_label = '%s.%s' % (self.app_label, self.object_name.lower())
             swapped_for = getattr(settings, self.swappable, None)
-            if swapped_for not in (None, model_label):
+            if swapped_for:
+                try:
+                    swapped_label, swapped_object = swapped_for.split('.')
+                except ValueError:
+                    # setting not in the format app_label.model_name
+                    # raising ImproperlyConfigured here causes problems with
+                    # test cleanup code - instead it is raised in get_user_model
+                    # or as part of validation.
+                    return swapped_for
+
+                if '%s.%s' % (swapped_label, swapped_object.lower()) not in (None, model_label):
                     return swapped_for
         return None
     swapped = property(_swapped)

tests/regressiontests/swappable_models/tests.py

@@ -9,6 +9,8 @@ from django.db.models.loading import cache
 from django.test import TestCase
 from django.test.utils import override_settings
 
+from regressiontests.swappable_models.models import Article
+
 
 class SwappableModelTests(TestCase):
     def setUp(self):
@@ -44,3 +46,13 @@ class SwappableModelTests(TestCase):
                        for ct in ContentType.objects.all()]
         self.assertIn(('swappable_models', 'alternatearticle'), apps_models)
         self.assertNotIn(('swappable_models', 'article'), apps_models)
+
+    @override_settings(TEST_ARTICLE_MODEL='swappable_models.article')
+    def test_case_insensitive(self):
+        "Model names are case insensitive. Check that model swapping honors this."
+        try:
+            Article.objects.all()
+        except AttributeError:
+            self.fail('Swappable model names should be case insensitive.')
+
+        self.assertIsNone(Article._meta.swapped)