[1.8.x] Fixed #25686 -- Fixed crash on routers without an allow_migrate() method.

Thanks Simon Charette for review.

django/db/utils.py

@@ -326,30 +326,35 @@ class ConnectionRouter(object):
                     method = router.allow_migrate
                 except AttributeError:
                     method = router.allow_syncdb
+                    has_deprecated_signature = True
                     warnings.warn(
                         'Router.allow_syncdb has been deprecated and will stop working in Django 1.9. '
                         'Rename the method to allow_migrate.',
                         RemovedInDjango19Warning, stacklevel=2)
+                else:
+                    if HAS_INSPECT_SIGNATURE:
+                        sig = inspect.signature(method)
+                        has_deprecated_signature = not any(
+                            p.kind == inspect.Parameter.VAR_KEYWORD for p in sig.parameters.values()
+                        )
+                    else:
+                        argspec = inspect.getargspec(method)
+                        has_deprecated_signature = len(argspec.args) == 3 and not argspec.keywords
+                    if has_deprecated_signature:
+                        # Raised here because allow_syncdb has to be called with
+                        # the deprecated signature but shouldn't show this
+                        # warning (only the deprecated method one)
+                        warnings.warn(
+                            "The signature of allow_migrate has changed from "
+                            "allow_migrate(self, db, model) to "
+                            "allow_migrate(self, db, app_label, model_name=None, **hints). "
+                            "Support for the old signature will be removed in Django 1.10.",
+                            RemovedInDjango110Warning)
             except AttributeError:
                 # If the router doesn't have a method, skip to the next one.
                 continue
 
-            if HAS_INSPECT_SIGNATURE:
-                sig = inspect.signature(router.allow_migrate)
-                has_deprecated_signature = not any(
-                    p.kind == inspect.Parameter.VAR_KEYWORD for p in sig.parameters.values()
-                )
-            else:
-                argspec = inspect.getargspec(router.allow_migrate)
-                has_deprecated_signature = len(argspec.args) == 3 and not argspec.keywords
-
             if has_deprecated_signature:
-                warnings.warn(
-                    "The signature of allow_migrate has changed from "
-                    "allow_migrate(self, db, model) to "
-                    "allow_migrate(self, db, app_label, model_name=None, **hints). "
-                    "Support for the old signature will be removed in Django 1.10.",
-                    RemovedInDjango110Warning)
                 model = hints.get('model')
                 allow = None if model is None else method(db, model)
             else:

docs/releases/1.8.7.txt

@@ -12,4 +12,5 @@ Bugfixes
 * Fixed a crash of the debug view during the autumn DST change when
   :setting:`USE_TZ` is ``False`` and ``pytz`` is installed.
 
-* ...
+* Fixed a regression in 1.8.6 that caused database routers without an
+  ``allow_migrate()`` method to crash (:ticket:`25686`).

tests/multiple_database/tests.py

@@ -956,6 +956,27 @@ class RouterTestCase(TestCase):
                 self.assertTrue(router.allow_migrate('default', 'app_label'))
                 self.assertEqual(force_text(recorded.pop().message), msg)
 
+    def test_allow_syncdb_deprecation(self):
+        class LegacyRouter(object):
+            def allow_syncdb(self, db, model):
+                assert db == 'default'
+                assert model is User
+                return True
+
+        with override_settings(DATABASE_ROUTERS=[LegacyRouter()]):
+            with warnings.catch_warnings(record=True) as recorded:
+                warnings.filterwarnings('always')
+                msg = (
+                    "Router.allow_syncdb has been deprecated and will stop "
+                    "working in Django 1.9. Rename the method to allow_migrate."
+                )
+                self.assertTrue(router.allow_migrate_model('default', User))
+                self.assertEqual(force_text(recorded.pop().message), msg)
+                self.assertEqual(recorded, [])
+
+                self.assertTrue(router.allow_migrate('default', 'app_label'))
+                self.assertEqual(force_text(recorded.pop().message), msg)
+
     def test_partial_router(self):
         "A router can choose to implement a subset of methods"
         dive = Book.objects.using('other').create(title="Dive into Python",