Fix bug in flush_user_profile().

Every time we updated a UserProfile object, we were calling
delete_display_recipient_cache(), which churns the cache and
does an extra database hop to find subscriptions.  This was
due to saying `updated_fields` instead of `update_fields`.

This made us prone to cache churn for fields like UserProfile.pointer
that are fairly volatile.

Now we use the helper function changed().  To prevent the
opposite problem, we use all the fields that could invalidate
the cache.

zerver/lib/cache.py

@@ -401,8 +401,7 @@ def flush_user_profile(sender, **kwargs):
     if changed(['is_active']):
         cache_delete(active_user_ids_cache_key(user_profile.realm_id))
 
-    if kwargs.get('updated_fields') is None or \
-            'email' in kwargs['update_fields']:
+    if changed(['email', 'full_name', 'short_name', 'id', 'is_mirror_dummy']):
         delete_display_recipient_cache(user_profile)
 
     # Invalidate our bots_in_realm info dict if any bot has

zerver/tests/test_home.py

@@ -178,7 +178,7 @@ class HomeTest(ZulipTestCase):
             with patch('zerver.lib.cache.cache_set') as cache_mock:
                 result = self._get_home_page(stream='Denmark')
 
-        self.assert_length(queries, 41)
+        self.assert_length(queries, 40)
         self.assert_length(cache_mock.call_args_list, 10)
 
         html = result.content.decode('utf-8')

zerver/tests/test_messages.py

@@ -2412,7 +2412,7 @@ class SoftDeactivationMessageTest(ZulipTestCase):
         self.assertNotEqual(idle_user_msg_list[-1].content, message)
         with queries_captured() as queries:
             maybe_catch_up_soft_deactivated_user(long_term_idle_user)
-        self.assert_length(queries, 8)
+        self.assert_length(queries, 7)
         self.assertFalse(long_term_idle_user.long_term_idle)
         self.assertEqual(last_realm_audit_log_entry(
             'user_soft_activated').modified_user, long_term_idle_user)

zerver/tests/test_signup.py

@@ -324,7 +324,7 @@ class LoginTest(ZulipTestCase):
         with queries_captured() as queries:
             self.register(self.nonreg_email('test'), "test")
         # Ensure the number of queries we make is not O(streams)
-        self.assert_length(queries, 68)
+        self.assert_length(queries, 67)
         user_profile = self.nonreg_user('test')
         self.assertEqual(get_session_dict_user(self.client.session), user_profile.id)
         self.assertFalse(user_profile.enable_stream_desktop_notifications)

zerver/tests/test_users.py

@@ -38,6 +38,7 @@ from zerver.lib.stream_topic import StreamTopicTarget
 from django.conf import settings
 
 import datetime
+import mock
 import os
 import sys
 import time
@@ -260,6 +261,21 @@ class UserProfileTest(ZulipTestCase):
         self.assertEqual(dct[hamlet.id], self.example_email("hamlet"))
         self.assertEqual(dct[othello.id], self.example_email("othello"))
 
+    def test_cache_invalidation(self):
+        # type: () -> None
+        hamlet = self.example_user('hamlet')
+        with mock.patch('zerver.lib.cache.delete_display_recipient_cache') as m:
+            hamlet.full_name = 'Hamlet Junior'
+            hamlet.save(update_fields=["full_name"])
+
+        self.assertTrue(m.called)
+
+        with mock.patch('zerver.lib.cache.delete_display_recipient_cache') as m:
+            hamlet.long_term_idle = True
+            hamlet.save(update_fields=["long_term_idle"])
+
+        self.assertFalse(m.called)
+
 class ActivateTest(ZulipTestCase):
     def test_basics(self):
         # type: () -> None