Raise an exception when getting state at an outlier (#12191)

It seems like calling `_get_state_group_for_events` for an event where the
state is unknown is an error. Accordingly, let's raise an exception rather than
silently returning an empty result.

tests/handlers/test_federation.py

@@ -20,17 +20,17 @@ from twisted.test.proto_helpers import MemoryReactor
 from synapse.api.constants import EventTypes
 from synapse.api.errors import AuthError, Codes, LimitExceededError, SynapseError
 from synapse.api.room_versions import RoomVersions
-from synapse.events import EventBase
+from synapse.events import EventBase, make_event_from_dict
 from synapse.federation.federation_base import event_from_pdu_json
 from synapse.logging.context import LoggingContext, run_in_background
 from synapse.rest import admin
 from synapse.rest.client import login, room
 from synapse.server import HomeServer
-from synapse.types import create_requester
 from synapse.util import Clock
 from synapse.util.stringutils import random_string
 
 from tests import unittest
+from tests.test_utils import event_injection
 
 logger = logging.getLogger(__name__)
 
@@ -39,7 +39,7 @@ def generate_fake_event_id() -> str:
     return "$fake_" + random_string(43)
 
 
-class FederationTestCase(unittest.HomeserverTestCase):
+class FederationTestCase(unittest.FederatingHomeserverTestCase):
     servlets = [
         admin.register_servlets,
         login.register_servlets,
@@ -219,40 +219,76 @@ class FederationTestCase(unittest.HomeserverTestCase):
         # create the room
         user_id = self.register_user("kermit", "test")
         tok = self.login("kermit", "test")
-        requester = create_requester(user_id)
 
         room_id = self.helper.create_room_as(room_creator=user_id, tok=tok)
+        room_version = self.get_success(self.store.get_room_version(room_id))
 
-        ev1 = self.helper.send(room_id, "first message", tok=tok)
+        # we need a user on the remote server to be a member, so that we can send
+        # extremity-causing events.
+        self.get_success(
+            event_injection.inject_member_event(
+                self.hs, room_id, f"@user:{self.OTHER_SERVER_NAME}", "join"
+            )
+        )
+
+        send_result = self.helper.send(room_id, "first message", tok=tok)
+        ev1 = self.get_success(
+            self.store.get_event(send_result["event_id"], allow_none=False)
+        )
+        current_state = self.get_success(
+            self.store.get_events_as_list(
+                (self.get_success(self.store.get_current_state_ids(room_id))).values()
+            )
+        )
 
         # Create "many" backward extremities. The magic number we're trying to
         # create more than is 5 which corresponds to the number of backward
         # extremities we slice off in `_maybe_backfill_inner`
+        federation_event_handler = self.hs.get_federation_event_handler()
         for _ in range(0, 8):
-            event_handler = self.hs.get_event_creation_handler()
-            event, context = self.get_success(
-                event_handler.create_event(
-                    requester,
+            event = make_event_from_dict(
+                self.add_hashes_and_signatures(
                     {
+                        "origin_server_ts": 1,
                         "type": "m.room.message",
                         "content": {
                             "msgtype": "m.text",
                             "body": "message connected to fake event",
                         },
                         "room_id": room_id,
-                        "sender": user_id,
+                        "sender": f"@user:{self.OTHER_SERVER_NAME}",
+                        "prev_events": [
+                            ev1.event_id,
+                            # We're creating an backward extremity each time thanks
+                            # to this fake event
+                            generate_fake_event_id(),
+                        ],
+                        # lazy: *everything* is an auth event
+                        "auth_events": [ev.event_id for ev in current_state],
+                        "depth": ev1.depth + 1,
                     },
-                    prev_event_ids=[
-                        ev1["event_id"],
-                        # We're creating an backward extremity each time thanks
-                        # to this fake event
-                        generate_fake_event_id(),
-                    ],
+                    room_version,
+                ),
+                room_version,
+            )
+
+            # we poke this directly into _process_received_pdu, to avoid the
+            # federation handler wanting to backfill the fake event.
+            self.get_success(
+                federation_event_handler._process_received_pdu(
+                    self.OTHER_SERVER_NAME, event, state=current_state
                 )
             )
-            self.get_success(
-                event_handler.handle_new_client_event(requester, event, context)
+
+        # we should now have 8 backwards extremities.
+        backwards_extremities = self.get_success(
+            self.store.db_pool.simple_select_list(
+                "event_backward_extremities",
+                keyvalues={"room_id": room_id},
+                retcols=["event_id"],
             )
+        )
+        self.assertEqual(len(backwards_extremities), 8)
 
         current_depth = 1
         limit = 100