Fixed #35724 -- Tested migration commands handling of distributed namespace packages.

Also increased coverage of module_loading.py.

tests/migrations/test_commands.py

@@ -4,6 +4,7 @@ import io
 import os
 import shutil
 import sys
+from pathlib import Path
 from unittest import mock
 
 from django.apps import apps
@@ -21,7 +22,7 @@ from django.db.backends.utils import truncate_name
 from django.db.migrations.exceptions import InconsistentMigrationHistory
 from django.db.migrations.recorder import MigrationRecorder
 from django.test import TestCase, override_settings, skipUnlessDBFeature
-from django.test.utils import captured_stdout
+from django.test.utils import captured_stdout, extend_sys_path
 from django.utils import timezone
 from django.utils.version import get_docs_version
 
@@ -1729,6 +1730,25 @@ class MakeMigrationsTests(MigrationTestBase):
             call_command("makemigrations", stdout=out)
         self.assertIn("0001_initial.py", out.getvalue())
 
+    def test_makemigrations_no_init_ambiguous(self):
+        """
+        Migration directories without an __init__.py file are not allowed if
+        there are multiple namespace search paths that resolve to them.
+        """
+        out = io.StringIO()
+        with self.temporary_migration_module(
+            module="migrations.test_migrations_no_init"
+        ) as migration_dir:
+            # Copy the project directory into another place under sys.path.
+            app_dir = Path(migration_dir).parent
+            os.remove(app_dir / "__init__.py")
+            project_dir = app_dir.parent
+            dest = project_dir.parent / "other_dir_in_path"
+            shutil.copytree(project_dir, dest)
+            with extend_sys_path(str(dest)):
+                call_command("makemigrations", stdout=out)
+        self.assertEqual("No changes detected\n", out.getvalue())
+
     def test_makemigrations_migrations_announce(self):
         """
         makemigrations announces the migration at the default verbosity level.

tests/migrations/test_writer.py

@@ -22,7 +22,8 @@ from django.core.validators import EmailValidator, RegexValidator
 from django.db import migrations, models
 from django.db.migrations.serializer import BaseSerializer
 from django.db.migrations.writer import MigrationWriter, OperationWriter
-from django.test import SimpleTestCase
+from django.test import SimpleTestCase, override_settings
+from django.test.utils import extend_sys_path
 from django.utils.deconstruct import deconstructible
 from django.utils.functional import SimpleLazyObject
 from django.utils.timezone import get_default_timezone, get_fixed_timezone
@@ -954,6 +955,29 @@ class WriterTests(SimpleTestCase):
                 writer = MigrationWriter(migration)
                 self.assertEqual(writer.path, expected_path)
 
+    @override_settings(
+        MIGRATION_MODULES={"namespace_app": "namespace_app.migrations"},
+        INSTALLED_APPS=[
+            "migrations.migrations_test_apps.distributed_app_location_2.namespace_app"
+        ],
+    )
+    def test_migration_path_distributed_namespace(self):
+        base_dir = os.path.dirname(os.path.dirname(__file__))
+        test_apps_dir = os.path.join(base_dir, "migrations", "migrations_test_apps")
+        expected_msg = (
+            "Could not locate an appropriate location to create "
+            "migrations package namespace_app.migrations. Make sure the toplevel "
+            "package exists and can be imported."
+        )
+        with extend_sys_path(
+            os.path.join(test_apps_dir, "distributed_app_location_1"),
+            os.path.join(test_apps_dir, "distributed_app_location_2"),
+        ):
+            migration = migrations.Migration("0001_initial", "namespace_app")
+            writer = MigrationWriter(migration)
+            with self.assertRaisesMessage(ValueError, expected_msg):
+                writer.path
+
     def test_custom_operation(self):
         migration = type(
             "Migration",