compose_views: Add `savepoint=False` to avoid creating savepoints.

'compose_views' is used inside an outer db transaction created in
'update_user_group_backend'.

`transaction.atomic()` block in 'compose_views' resulted in
savepoint creation.

This commit adds `savepoint=False` to avoid that.

zerver/tests/test_subs.py

@@ -9,6 +9,7 @@ from unittest import mock
 import orjson
 from django.conf import settings
 from django.core.exceptions import ValidationError
+from django.db import transaction
 from django.http import HttpResponse
 from django.utils.timezone import now as timezone_now
 from typing_extensions import override
@@ -4016,7 +4017,9 @@ class SubscriptionRestApiTest(ZulipTestCase):
         def thunk2() -> HttpResponse:
             raise JsonableError("random failure")
 
-        with self.assertRaises(JsonableError):
+        with transaction.atomic(), self.assertRaises(JsonableError):
+            # The atomic() wrapper helps to avoid JsonableError breaking
+            # the test's transaction.
             compose_views([thunk1, thunk2])
 
         user_profile = self.example_user("hamlet")

zerver/transaction_tests/test_user_groups.py

@@ -28,7 +28,6 @@ def dev_update_subgroups(
     assert BARRIER is not None
     try:
         with (
-            transaction.atomic(),
             mock.patch("zerver.lib.user_groups.access_user_group_for_update") as m,
         ):
 

zerver/views/streams.py

@@ -468,7 +468,7 @@ def compose_views(thunks: list[Callable[[], HttpResponse]]) -> dict[str, Any]:
     """
 
     json_dict: dict[str, Any] = {}
-    with transaction.atomic():
+    with transaction.atomic(savepoint=False):
         for thunk in thunks:
             response = thunk()
             json_dict.update(orjson.loads(response.content))

zerver/views/user_groups.py

@@ -468,6 +468,7 @@ def remove_subgroups_from_group_backend(
 
 @require_member_or_admin
 @typed_endpoint
+@transaction.atomic(durable=True)
 def update_subgroups_of_user_group(
     request: HttpRequest,
     user_profile: UserProfile,