lint: Ban general use of user_profile.save().

This often can cause minor caching problems.

Obviously, it'd be better if we had access to the AST and thus could
do this rule for UserProfile objects in general.

tools/linter_lib/custom_check.py

@@ -241,6 +241,14 @@ def build_custom_checkers(by_lang):
          'description': '@login_required is unsupported; use @zulip_login_required',
          'good_lines': ['@zulip_login_required', '# foo @login_required'],
          'bad_lines': ['@login_required', ' @login_required']},
+        {'pattern': '^user_profile[.]save[(][)]',
+         'description': 'Always pass update_fields when saving user_profile objects',
+         'exclude_line': set([
+             ('zerver/lib/actions.py', "user_profile.save()  # Can't use update_fields because of how the foreign key works."),
+         ]),
+         'exclude': set(['zerver/tests', 'zerver/lib/create_user.py']),
+         'good_lines': ['user_profile.save(update_fields=["pointer"])'],
+         'bad_lines': ['user_profile.save()']},
         {'pattern': '^[^"]*"[^"]*"%\(',
          'description': 'Missing space around "%"',
          'good_lines': ['"%s" % ("foo")', '"%s" % (foo)'],

zerver/lib/actions.py

@@ -2529,7 +2529,7 @@ def check_change_full_name(user_profile, full_name_raw, acting_user):
 def do_change_bot_owner(user_profile, bot_owner, acting_user):
     # type: (UserProfile, UserProfile, UserProfile) -> None
     user_profile.bot_owner = bot_owner
-    user_profile.save()
+    user_profile.save()  # Can't use update_fields because of how the foreign key works.
     event_time = timezone_now()
     RealmAuditLog.objects.create(realm=user_profile.realm, acting_user=acting_user,
                                  modified_user=user_profile, event_type='bot_owner_changed',

zerver/views/email_log.py

@@ -88,9 +88,10 @@ def generate_all_emails(request):
     user_profile = get_user(registered_email, realm)
     result = client.get(url)
     assert result.status_code == 200
-    # Reset the email value
+
+    # Reset the email value so we can run this again
     user_profile.email = registered_email
-    user_profile.save()
+    user_profile.save(update_fields=['email'])
 
     # Follow up day1 day2 emails
     enqueue_welcome_emails(user_profile)