Stop testing for inclusion in INSTALLED_APPS.

Removed some exception masking in the comments app that was harmful and
couldn't be preserved easily.

django/contrib/admin/templatetags/admin_static.py

@@ -1,9 +1,9 @@
-from django.conf import settings
+from django.core.apps import app_cache
 from django.template import Library
 
 register = Library()
 
-if 'django.contrib.staticfiles' in settings.INSTALLED_APPS:
+if app_cache.has_app('django.contrib.staticfiles'):
     from django.contrib.staticfiles.templatetags.staticfiles import static
 else:
     from django.templatetags.static import static

django/contrib/comments/__init__.py

@@ -2,6 +2,7 @@ from importlib import import_module
 import warnings
 from django.conf import settings
 from django.core import urlresolvers
+from django.core.apps import app_cache
 from django.core.exceptions import ImproperlyConfigured
 from django.contrib.comments.models import Comment
 from django.contrib.comments.forms import CommentForm
@@ -14,20 +15,12 @@ def get_comment_app():
     """
     Get the comment app (i.e. "django.contrib.comments") as defined in the settings
     """
-    # Make sure the app's in INSTALLED_APPS
-    comments_app = get_comment_app_name()
-    if comments_app not in settings.INSTALLED_APPS:
-        raise ImproperlyConfigured("The COMMENTS_APP (%r) "\
-                                   "must be in INSTALLED_APPS" % settings.COMMENTS_APP)
-
-    # Try to import the package
     try:
-        package = import_module(comments_app)
-    except ImportError as e:
-        raise ImproperlyConfigured("The COMMENTS_APP setting refers to "\
-                                   "a non-existing package. (%s)" % e)
-
-    return package
+        app_config = app_cache.get_app_config(get_comment_app_name().rpartition(".")[2])
+    except LookupError:
+        raise ImproperlyConfigured("The COMMENTS_APP (%r) "
+                                   "must be in INSTALLED_APPS" % settings.COMMENTS_APP)
+    return app_config.app_module
 
 def get_comment_app_name():
     """

django/contrib/messages/tests/base.py

@@ -1,4 +1,4 @@
-from unittest import skipIf
+from unittest import skipUnless
 
 from django import http
 from django.conf import settings, global_settings
@@ -7,14 +7,15 @@ from django.contrib.messages.api import MessageFailure
 from django.contrib.messages.constants import DEFAULT_LEVELS
 from django.contrib.messages.storage import default_storage, base
 from django.contrib.messages.storage.base import Message
+from django.core.apps import app_cache
 from django.core.urlresolvers import reverse
 from django.test.utils import override_settings
 from django.utils.translation import ugettext_lazy
 
 
 def skipUnlessAuthIsInstalled(func):
-    return skipIf(
-        'django.contrib.auth' not in settings.INSTALLED_APPS,
+    return skipUnless(
+        app_cache.has_app('django.contrib.auth'),
         "django.contrib.auth isn't installed")(func)
 
 
@@ -219,8 +220,6 @@ class BaseTests(object):
             self.assertContains(response, msg)
 
     @override_settings(
-        INSTALLED_APPS=filter(
-            lambda app: app != 'django.contrib.messages', settings.INSTALLED_APPS),
         MIDDLEWARE_CLASSES=filter(
             lambda m: 'MessageMiddleware' not in m, settings.MIDDLEWARE_CLASSES),
         TEMPLATE_CONTEXT_PROCESSORS=filter(
@@ -233,6 +232,7 @@ class BaseTests(object):
         Tests that, when the middleware is disabled, an exception is raised
         when one attempts to store a message.
         """
+        with app_cache._without_app('django.contrib.messages'):
             data = {
                 'messages': ['Test message %d' % x for x in range(5)],
             }
@@ -244,8 +244,6 @@ class BaseTests(object):
                                   data, follow=True)
 
     @override_settings(
-        INSTALLED_APPS=filter(
-            lambda app: app != 'django.contrib.messages', settings.INSTALLED_APPS),
         MIDDLEWARE_CLASSES=filter(
             lambda m: 'MessageMiddleware' not in m, settings.MIDDLEWARE_CLASSES),
         TEMPLATE_CONTEXT_PROCESSORS=filter(
@@ -258,6 +256,7 @@ class BaseTests(object):
         Tests that, when the middleware is disabled, an exception is not
         raised if 'fail_silently' = True
         """
+        with app_cache._without_app('django.contrib.messages'):
             data = {
                 'messages': ['Test message %d' % x for x in range(5)],
                 'fail_silently': True,

django/contrib/redirects/middleware.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 from django.conf import settings
 from django.contrib.redirects.models import Redirect
 from django.contrib.sites.models import get_current_site
+from django.core.apps import app_cache
 from django.core.exceptions import ImproperlyConfigured
 from django import http
 
@@ -14,7 +15,7 @@ class RedirectFallbackMiddleware(object):
     response_redirect_class = http.HttpResponsePermanentRedirect
 
     def __init__(self):
-        if 'django.contrib.sites' not in settings.INSTALLED_APPS:
+        if not app_cache.has_app('django.contrib.sites'):
             raise ImproperlyConfigured(
                 "You cannot use RedirectFallbackMiddleware when "
                 "django.contrib.sites is not installed."

django/contrib/redirects/tests.py

@@ -1,6 +1,7 @@
 from django import http
 from django.conf import settings
 from django.contrib.sites.models import Site
+from django.core.apps import app_cache
 from django.core.exceptions import ImproperlyConfigured
 from django.test import TestCase
 from django.test.utils import override_settings
@@ -56,10 +57,8 @@ class RedirectTests(TestCase):
         response = self.client.get('/initial')
         self.assertEqual(response.status_code, 410)
 
-    @override_settings(
-        INSTALLED_APPS=[app for app in settings.INSTALLED_APPS
-                        if app != 'django.contrib.sites'])
     def test_sites_not_installed(self):
+        with app_cache._without_app('django.contrib.sites'):
             with self.assertRaises(ImproperlyConfigured):
                 RedirectFallbackMiddleware()
 

django/contrib/sitemaps/tests/test_flatpages.py

@@ -3,13 +3,14 @@ from __future__ import unicode_literals
 from unittest import skipUnless
 
 from django.conf import settings
+from django.core.apps import app_cache
 
 from .base import SitemapTestsBase
 
 
 class FlatpagesSitemapTests(SitemapTestsBase):
 
-    @skipUnless("django.contrib.flatpages" in settings.INSTALLED_APPS,
+    @skipUnless(app_cache.has_app('django.contrib.flatpages'),
                 "django.contrib.flatpages app not installed.")
     def test_flatpage_sitemap(self):
         "Basic FlatPage sitemap test"

django/contrib/sitemaps/tests/test_http.py

@@ -118,7 +118,7 @@ class HTTPSitemapTests(SitemapTestsBase):
 """ % date.today()
             self.assertXMLEqual(response.content.decode('utf-8'), expected_content)
 
-    @skipUnless("django.contrib.sites" in settings.INSTALLED_APPS,
+    @skipUnless(app_cache.has_app('django.contrib.sites'),
                 "django.contrib.sites app not installed.")
     def test_sitemap_get_urls_no_site_1(self):
         """

django/core/apps/cache.py

@@ -298,6 +298,18 @@ class AppCache(object):
         models[model_name] = model
         self._get_models_cache.clear()
 
+    def has_app(self, app_name):
+        """
+        Returns the application config if one is registered and None otherwise.
+
+        It's safe to call this method at import time, even while the app cache
+        is being populated. It returns None for apps that aren't loaded yet.
+        """
+        app_config = self.app_configs.get(app_name.rpartition(".")[2])
+        if app_config is not None and app_config.name != app_name:
+            app_config = None
+        return app_config
+
     def has_model(self, app_label, model_name):
         """
         Returns the model class if one is registered and None otherwise.

django/test/client.py

@@ -10,6 +10,7 @@ from io import BytesIO
 
 from django.conf import settings
 from django.contrib.auth import authenticate, login, logout, get_user_model
+from django.core.apps import app_cache
 from django.core.handlers.base import BaseHandler
 from django.core.handlers.wsgi import WSGIRequest
 from django.core.signals import (request_started, request_finished,
@@ -389,7 +390,7 @@ class Client(RequestFactory):
         """
         Obtains the current session variables.
         """
-        if 'django.contrib.sessions' in settings.INSTALLED_APPS:
+        if app_cache.has_app('django.contrib.sessions'):
             engine = import_module(settings.SESSION_ENGINE)
             cookie = self.cookies.get(settings.SESSION_COOKIE_NAME, None)
             if cookie:
@@ -550,7 +551,7 @@ class Client(RequestFactory):
         """
         user = authenticate(**credentials)
         if (user and user.is_active and
-                'django.contrib.sessions' in settings.INSTALLED_APPS):
+                app_cache.has_app('django.contrib.sessions')):
             engine = import_module(settings.SESSION_ENGINE)
 
             # Create a fake request that goes through request middleware

tests/comment_tests/tests/test_app_api.py

@@ -2,6 +2,7 @@ from django.conf import settings
 from django.contrib import comments
 from django.contrib.comments.models import Comment
 from django.contrib.comments.forms import CommentForm
+from django.core.apps import app_cache
 from django.core.exceptions import ImproperlyConfigured
 from django.test.utils import override_settings
 from django.utils import six
@@ -15,14 +16,6 @@ class CommentAppAPITests(CommentTestCase):
     def testGetCommentApp(self):
         self.assertEqual(comments.get_comment_app(), comments)
 
-    @override_settings(
-        COMMENTS_APP='missing_app',
-        INSTALLED_APPS=list(settings.INSTALLED_APPS) + ['missing_app'],
-    )
-    def testGetMissingCommentApp(self):
-        with six.assertRaisesRegex(self, ImproperlyConfigured, 'missing_app'):
-            comments.get_comment_app()
-
     def testGetForm(self):
         self.assertEqual(comments.get_form(), CommentForm)
 
@@ -42,14 +35,16 @@ class CommentAppAPITests(CommentTestCase):
         self.assertEqual(comments.get_approve_url(c), "/approve/12345/")
 
 
-@override_settings(
-    COMMENTS_APP='comment_tests.custom_comments',
-    INSTALLED_APPS=list(settings.INSTALLED_APPS) + [
-        'comment_tests.custom_comments'],
-)
+@override_settings(COMMENTS_APP='comment_tests.custom_comments')
 class CustomCommentTest(CommentTestCase):
     urls = 'comment_tests.urls'
 
+    def setUp(self):
+        self._with_custom_comments = app_cache._begin_with_app('comment_tests.custom_comments')
+
+    def tearDown(self):
+        app_cache._end_with_app(self._with_custom_comments)
+
     def testGetCommentApp(self):
         from comment_tests import custom_comments
         self.assertEqual(comments.get_comment_app(), custom_comments)