Fixed #21060 -- Refactored admin's autodiscover method to make it reusable.

We want to be able to use it for instance for discovering `tasks.py` modules
inside the INSTALLED_APPS.

This commit therefore moves the logic to `autodiscover_modules` method in
django.utils.module_loading.

django/contrib/admin/__init__.py

@@ -7,35 +7,8 @@ from django.contrib.admin.sites import AdminSite, site
 from django.contrib.admin.filters import (ListFilter, SimpleListFilter,
     FieldListFilter, BooleanFieldListFilter, RelatedFieldListFilter,
     ChoicesFieldListFilter, DateFieldListFilter, AllValuesFieldListFilter)
+from django.utils.module_loading import autodiscover_modules
 
 
 def autodiscover():
-    """
-    Auto-discover INSTALLED_APPS admin.py modules and fail silently when
-    not present. This forces an import on them to register any admin bits they
-    may want.
-    """
-
-    import copy
-    from importlib import import_module
-    from django.conf import settings
-    from django.utils.module_loading import module_has_submodule
-
-    for app in settings.INSTALLED_APPS:
-        mod = import_module(app)
-        # Attempt to import the app's admin module.
-        try:
-            before_import_registry = copy.copy(site._registry)
-            import_module('%s.admin' % app)
-        except:
-            # Reset the model registry to the state before the last import as
-            # this import will have to reoccur on the next request and this
-            # could raise NotRegistered and AlreadyRegistered exceptions
-            # (see #8245).
-            site._registry = before_import_registry
-
-            # Decide whether to bubble up this error. If the app just
-            # doesn't have an admin module, we can ignore the error
-            # attempting to import it, otherwise we want it to bubble up.
-            if module_has_submodule(mod, 'admin'):
-                raise
+    autodiscover_modules('admin', register_to=site)

django/utils/module_loading.py

 from __future__ import absolute_import  # Avoid importing `importlib` from this package.
 
+import copy
 import imp
 from importlib import import_module
 import os
@@ -34,6 +35,43 @@ def import_by_path(dotted_path, error_prefix=''):
     return attr
 
 
+def autodiscover_modules(*args, **kwargs):
+    """
+    Auto-discover INSTALLED_APPS modules and fail silently when
+    not present. This forces an import on them to register any admin bits they
+    may want.
+
+    You may provide a register_to keyword parameter as a way to access a
+    registry. This register_to object must have a _registry instance variable
+    to access it.
+    """
+    from django.conf import settings
+
+    register_to = kwargs.get('register_to')
+    for app in settings.INSTALLED_APPS:
+        mod = import_module(app)
+        # Attempt to import the app's module.
+        try:
+            if register_to:
+                before_import_registry = copy.copy(register_to._registry)
+
+            for module_to_search in args:
+                import_module('%s.%s' % (app, module_to_search))
+        except:
+            # Reset the model registry to the state before the last import as
+            # this import will have to reoccur on the next request and this
+            # could raise NotRegistered and AlreadyRegistered exceptions
+            # (see #8245).
+            if register_to:
+                register_to._registry = before_import_registry
+
+            # Decide whether to bubble up this error. If the app just
+            # doesn't have an admin module, we can ignore the error
+            # attempting to import it, otherwise we want it to bubble up.
+            if module_has_submodule(mod, module_to_search):
+                raise
+
+
 def module_has_submodule(package, module_name):
     """See if 'module' is in 'package'."""
     name = ".".join([package.__name__, module_name])

tests/utils_tests/test_module/__init__.py

+class SiteMock(object):
+    _registry = {}
+site = SiteMock()

tests/utils_tests/test_module/another_bad_module.py

+from . import site
+content = 'Another Bad Module'
+
+site._registry.update({
+    'foo': 'bar',
+})
+
+raise Exception('Some random exception.')

tests/utils_tests/test_module/another_good_module.py

+content = 'Another Good Module'

tests/utils_tests/test_module_loading.py

@@ -6,7 +6,10 @@ import unittest
 from zipimport import zipimporter
 
 from django.core.exceptions import ImproperlyConfigured
-from django.utils.module_loading import import_by_path, module_has_submodule
+from django.test import SimpleTestCase
+from django.test.utils import override_settings
+from django.utils import six
+from django.utils.module_loading import autodiscover_modules, import_by_path, module_has_submodule
 from django.utils._os import upath
 
 
@@ -130,6 +133,32 @@ class ModuleImportTestCase(unittest.TestCase):
         self.assertIsNotNone(traceback.tb_next.tb_next,
             'Should have more than the calling frame in the traceback.')
 
+@override_settings(INSTALLED_APPS=('utils_tests.test_module',))
+class AutodiscoverModulesTestCase(SimpleTestCase):
+
+    def test_autodiscover_modules_found(self):
+        autodiscover_modules('good_module')
+
+    def test_autodiscover_modules_not_found(self):
+        autodiscover_modules('missing_module')
+
+    def test_autodiscover_modules_found_but_bad_module(self):
+        with six.assertRaisesRegex(self, ImportError, "No module named '?a_package_name_that_does_not_exist'?"):
+            autodiscover_modules('bad_module')
+
+    def test_autodiscover_modules_several_one_bad_module(self):
+        with six.assertRaisesRegex(self, ImportError, "No module named '?a_package_name_that_does_not_exist'?"):
+            autodiscover_modules('good_module', 'bad_module')
+
+    def test_autodiscover_modules_several_found(self):
+        autodiscover_modules('good_module', 'another_good_module')
+
+    def test_validate_registry_keeps_intact(self):
+        from .test_module import site
+        with six.assertRaisesRegex(self, Exception, "Some random exception."):
+            autodiscover_modules('another_bad_module', register_to=site)
+        self.assertEqual(site._registry, {})
+
 
 class ProxyFinder(object):
     def __init__(self):