Fixed #23406 -- Allowed migrations to be loaded from .pyc files.

5 files changed, 53 insertions, 11 deletions

diff --git a/django/db/migrations/loader.py b/django/db/migrations/loader.py
index c4d26d1186..4147cc3f09 100644
--- a/django/db/migrations/loader.py
+++ b/django/db/migrations/loader.py
@@ -1,4 +1,4 @@
-import os
+import pkgutil
 import sys
 from importlib import import_module, reload
 
@@ -97,17 +97,20 @@ class MigrationLoader:
                 if was_loaded:
                     reload(module)
             self.migrated_apps.add(app_config.label)
-            directory = os.path.dirname(module.__file__)
-            # Scan for .py files
-            migration_names = set()
-            for name in os.listdir(directory):
-                if name.endswith(".py"):
-                    import_name = name.rsplit(".", 1)[0]
-                    if import_name[0] not in "_.~":
-                        migration_names.add(import_name)
-            # Load them
+            migration_names = {name for _, name, is_pkg in pkgutil.iter_modules(module.__path__) if not is_pkg}
+            # Load migrations
             for migration_name in migration_names:
-                migration_module = import_module("%s.%s" % (module_name, migration_name))
+                migration_path = '%s.%s' % (module_name, migration_name)
+                try:
+                    migration_module = import_module(migration_path)
+                except ImportError as e:
+                    if 'bad magic number' in str(e):
+                        raise ImportError(
+                            "Couldn't import %r as it appears to be a stale "
+                            ".pyc file." % migration_path
+                        ) from e
+                    else:
+                        raise
                 if not hasattr(migration_module, "Migration"):
                     raise BadMigrationError(
                         "Migration %s in app %s has no Migration class" % (migration_name, app_config.label)
diff --git a/docs/releases/2.1.txt b/docs/releases/2.1.txt
index 463fad0b6c..2b1d6dabdc 100644
--- a/docs/releases/2.1.txt
+++ b/docs/releases/2.1.txt
@@ -194,6 +194,8 @@ Migrations
 
 * Added support for serialization of ``functools.partialmethod`` objects.
 
+* To support frozen environments, migrations may be loaded from ``.pyc`` files.
+
 Models
 ~~~~~~
 
@@ -366,6 +368,9 @@ Miscellaneous
   with such passwords from requesting a password reset. Audit your code to
   confirm that your usage of these APIs don't rely on the old behavior.
 
+* Since migrations are now loaded from ``.pyc`` files, you might need to delete
+  them if you're working in a mixed Python 2 and Python 3 environment.
+
 .. _deprecated-features-2.1:
 
 Features deprecated in 2.1
diff --git a/tests/migrations/test_loader.py b/tests/migrations/test_loader.py
index e0e7e3d258..eade230640 100644
--- a/tests/migrations/test_loader.py
+++ b/tests/migrations/test_loader.py
@@ -1,3 +1,6 @@
+import compileall
+import os
+
 from django.db import connection, connections
 from django.db.migrations.exceptions import (
     AmbiguityError, InconsistentMigrationHistory, NodeNotFoundError,
@@ -6,6 +9,8 @@ from django.db.migrations.loader import MigrationLoader
 from django.db.migrations.recorder import MigrationRecorder
 from django.test import TestCase, modify_settings, override_settings
 
+from .test_base import MigrationTestBase
+
 
 class RecorderTests(TestCase):
     """
@@ -494,3 +499,32 @@ class LoaderTests(TestCase):
             ('app1', '4_auto'),
         }
         self.assertEqual(plan, expected_plan)
+
+
+class PycLoaderTests(MigrationTestBase):
+
+    def test_valid(self):
+        """
+        To support frozen environments, MigrationLoader loads .pyc migrations.
+        """
+        with self.temporary_migration_module(module='migrations.test_migrations') as migration_dir:
+            # Compile .py files to .pyc files and delete .py files.
+            compileall.compile_dir(migration_dir, force=True, quiet=1, legacy=True)
+            for name in os.listdir(migration_dir):
+                if name.endswith('.py'):
+                    os.remove(os.path.join(migration_dir, name))
+            loader = MigrationLoader(connection)
+            self.assertIn(('migrations', '0001_initial'), loader.disk_migrations)
+
+    def test_invalid(self):
+        """
+        MigrationLoader reraises ImportErrors caused by "bad magic number" pyc
+        files with a more helpful message.
+        """
+        with self.temporary_migration_module(module='migrations.test_migrations_bad_pyc'):
+            msg = (
+                "Couldn't import '\w+.migrations.0001_initial' as it appears "
+                "to be a stale .pyc file."
+            )
+            with self.assertRaisesRegex(ImportError, msg):
+                MigrationLoader(connection)
diff --git a/tests/migrations/test_migrations_bad_pyc/0001_initial.pyc b/tests/migrations/test_migrations_bad_pyc/0001_initial.pyc
new file mode 100644
index 0000000000..07854f4aeb
--- /dev/null
+++ b/tests/migrations/test_migrations_bad_pyc/0001_initial.pyc
diff --git a/tests/migrations/test_migrations_bad_pyc/__init__.py b/tests/migrations/test_migrations_bad_pyc/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/migrations/test_migrations_bad_pyc/__init__.py