Fixed #25109 -- Stopped silencing explicitly specified migration modules import errors.

Thanks Tim for the review.

4 files changed, 28 insertions, 6 deletions

diff --git a/django/db/migrations/loader.py b/django/db/migrations/loader.py
index 262378d1dc..c78aaed573 100644
--- a/django/db/migrations/loader.py
+++ b/django/db/migrations/loader.py
@@ -54,11 +54,16 @@ class MigrationLoader(object):
 
     @classmethod
     def migrations_module(cls, app_label):
+        """
+        Return the path to the migrations module for the specified app_label
+        and a boolean indicating if the module is specified in
+        settings.MIGRATION_MODULE.
+        """
         if app_label in settings.MIGRATION_MODULES:
-            return settings.MIGRATION_MODULES[app_label]
+            return settings.MIGRATION_MODULES[app_label], True
         else:
             app_package_name = apps.get_app_config(app_label).name
-            return '%s.%s' % (app_package_name, MIGRATIONS_MODULE_NAME)
+            return '%s.%s' % (app_package_name, MIGRATIONS_MODULE_NAME), False
 
     def load_disk(self):
         """
@@ -69,7 +74,7 @@ class MigrationLoader(object):
         self.migrated_apps = set()
         for app_config in apps.get_app_configs():
             # Get the migrations module directory
-            module_name = self.migrations_module(app_config.label)
+            module_name, explicit = self.migrations_module(app_config.label)
             if module_name is None:
                 self.unmigrated_apps.add(app_config.label)
                 continue
@@ -79,7 +84,8 @@ class MigrationLoader(object):
             except ImportError as e:
                 # I hate doing this, but I don't want to squash other import errors.
                 # Might be better to try a directory check directly.
-                if "No module named" in str(e) and MIGRATIONS_MODULE_NAME in str(e):
+                if ((explicit and self.ignore_no_migrations) or (
+                        not explicit and "No module named" in str(e) and MIGRATIONS_MODULE_NAME in str(e))):
                     self.unmigrated_apps.add(app_config.label)
                     continue
                 raise
diff --git a/django/db/migrations/questioner.py b/django/db/migrations/questioner.py
index 593e0ace3b..df08508a10 100644
--- a/django/db/migrations/questioner.py
+++ b/django/db/migrations/questioner.py
@@ -37,7 +37,7 @@ class MigrationQuestioner(object):
             app_config = apps.get_app_config(app_label)
         except LookupError:         # It's a fake app.
             return self.defaults.get("ask_initial", False)
-        migrations_import_path = MigrationLoader.migrations_module(app_config.label)
+        migrations_import_path, _ = MigrationLoader.migrations_module(app_config.label)
         if migrations_import_path is None:
             # It's an application with migrations disabled.
             return self.defaults.get("ask_initial", False)
diff --git a/django/db/migrations/writer.py b/django/db/migrations/writer.py
index 137f83dbc0..7c39cdc931 100644
--- a/django/db/migrations/writer.py
+++ b/django/db/migrations/writer.py
@@ -221,7 +221,7 @@ class MigrationWriter(object):
 
     @property
     def basedir(self):
-        migrations_package_name = MigrationLoader.migrations_module(self.migration.app_label)
+        migrations_package_name, _ = MigrationLoader.migrations_module(self.migration.app_label)
 
         if migrations_package_name is None:
             raise ValueError(
diff --git a/tests/migrations/test_loader.py b/tests/migrations/test_loader.py
index b8c2cd8142..5b31fcbd2c 100644
--- a/tests/migrations/test_loader.py
+++ b/tests/migrations/test_loader.py
@@ -205,6 +205,22 @@ class LoaderTests(TestCase):
         self.assertEqual(migration_loader.migrated_apps, set())
         self.assertEqual(migration_loader.unmigrated_apps, {'migrated_app'})
 
+    @override_settings(
+        INSTALLED_APPS=['migrations.migrations_test_apps.migrated_app'],
+        MIGRATION_MODULES={'migrated_app': 'missing-module'},
+    )
+    def test_explicit_missing_module(self):
+        """
+        If a MIGRATION_MODULES override points to a missing module, the error
+        raised during the importation attempt should be propagated unless
+        `ignore_no_migrations=True`.
+        """
+        with self.assertRaisesMessage(ImportError, 'missing-module'):
+            migration_loader = MigrationLoader(connection)
+        migration_loader = MigrationLoader(connection, ignore_no_migrations=True)
+        self.assertEqual(migration_loader.migrated_apps, set())
+        self.assertEqual(migration_loader.unmigrated_apps, {'migrated_app'})
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_squashed"})
     def test_loading_squashed(self):
         "Tests loading a squashed migration"