settings: Add new DEBUG_RATE_LIMITING setting.

This exists primarily in order to allow us to mock settings.DEBUG for
the purposes of rate limiting, without actually mocking
settings.DEBUG, which I suspect Django never intended one to do, and
thus caused some very strange test failures (see
https://github.com/zulip/zulip/pull/776 for details).

zerver/decorator.py

@@ -466,7 +466,8 @@ def client_is_exempt_from_rate_limiting(request):
     # Don't rate limit requests from Django that come from our own servers,
     # and don't rate-limit dev instances
     return ((request.client and request.client.name.lower() == 'internal')
-           and (is_local_addr(request.META['REMOTE_ADDR']) or settings.DEBUG))
+           and (is_local_addr(request.META['REMOTE_ADDR']) or
+                settings.DEBUG_RATE_LIMITING))
 
 def internal_notify_view(view_func):
     # type: (ViewFuncT) -> ViewFuncT

zerver/tests/test_decorators.py

@@ -263,7 +263,7 @@ class RateLimitTestCase(TestCase):
         with self.settings(RATE_LIMITING=True):
             with mock.patch('zerver.decorator.rate_limit_user') as rate_limit_mock:
                 with self.errors_disallowed():
-                    with self.settings(DEBUG=True):
+                    with self.settings(DEBUG_RATE_LIMITING=True):
                         self.assertEqual(f(req), 'some value')
 
         self.assertFalse(rate_limit_mock.called)

zproject/settings.py

@@ -404,6 +404,7 @@ CACHES = {
 RATE_LIMITING_RULES = [
     (60, 100),     # 100 requests max every minute
     ]
+DEBUG_RATE_LIMITING = DEBUG
 
 ########################################################################
 # SECURITY SETTINGS