Fix #62 -- Address crash of system checks with empty migrations directory.

Author: oliverhaas

CHANGELOG.rst

@@ -1,3 +1,11 @@
+1.2.2
+=====
+
+:release-date: not-released
+
+- Address crash of system checks when an installed app has an empty
+  `migrations` directory. (#62)
+
 1.2.1
 =====
 

syzygy/checks.py

@@ -30,6 +30,10 @@ def check_migrations(app_configs, **kwargs):
         except ImportError:
             # This is not the place to deal with migration issues.
             continue
+        if module.__file__ is None:
+            # Skip empty migration folders, which can happen
+            # for example when switching between branches.
+            continue
         directory = os.path.dirname(module.__file__)
         migration_names = set()
         for name in os.listdir(directory):

tests/test_checks.py

@@ -29,3 +29,10 @@ def test_ambiguous_stage(self):
                 id="migrations.0001",
             ),
         )
+
+    def test_empty_migration_folder(self):
+        with self.settings(MIGRATION_MODULES={"tests": "tests.test_migrations.empty"}):
+            checks = run_checks(
+                app_configs=[apps.get_app_config("tests")], tags={"migrations"}
+            )
+        self.assertEqual(len(checks), 0)

tests/test_migrations/empty/.gitkeep

@@ -0,0 +1 @@
+