Fix bug in EventContext.deserialize. (matrix-org#7393)

This caused `prev_state_ids` to be incorrect if the state event was not
replacing an existing state entry.

changelog.d/7393.bugfix

@@ -0,0 +1 @@
+Fix bug in `EventContext.deserialize`.

synapse/events/snapshot.py

@@ -322,11 +322,14 @@ def _fill_out_state(self):
         self._current_state_ids = yield self._storage.state.get_state_ids_for_group(
             self.state_group
         )
-        if self._prev_state_id and self._event_state_key is not None:
+        if self._event_state_key is not None:
             self._prev_state_ids = dict(self._current_state_ids)
 
             key = (self._event_type, self._event_state_key)
-            self._prev_state_ids[key] = self._prev_state_id
+            if self._prev_state_id:
+                self._prev_state_ids[key] = self._prev_state_id
+            else:
+                self._prev_state_ids.pop(key, None)
         else:
             self._prev_state_ids = self._current_state_ids
 

tests/events/test_snapshot.py

@@ -0,0 +1,100 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.events.snapshot import EventContext
+from synapse.rest import admin
+from synapse.rest.client.v1 import login, room
+
+from tests import unittest
+from tests.test_utils.event_injection import create_event
+
+
+class TestEventContext(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def prepare(self, reactor, clock, hs):
+        self.store = hs.get_datastore()
+        self.storage = hs.get_storage()
+
+        self.user_id = self.register_user("u1", "pass")
+        self.user_tok = self.login("u1", "pass")
+        self.room_id = self.helper.create_room_as(tok=self.user_tok)
+
+    def test_serialize_deserialize_msg(self):
+        """Test that an EventContext for a message event is the same after
+        serialize/deserialize.
+        """
+
+        event, context = create_event(
+            self.hs, room_id=self.room_id, type="m.test", sender=self.user_id,
+        )
+
+        self._check_serialize_deserialize(event, context)
+
+    def test_serialize_deserialize_state_no_prev(self):
+        """Test that an EventContext for a state event (with not previous entry)
+        is the same after serialize/deserialize.
+        """
+        event, context = create_event(
+            self.hs,
+            room_id=self.room_id,
+            type="m.test",
+            sender=self.user_id,
+            state_key="",
+        )
+
+        self._check_serialize_deserialize(event, context)
+
+    def test_serialize_deserialize_state_prev(self):
+        """Test that an EventContext for a state event (which replaces a
+        previous entry) is the same after serialize/deserialize.
+        """
+        event, context = create_event(
+            self.hs,
+            room_id=self.room_id,
+            type="m.room.member",
+            sender=self.user_id,
+            state_key=self.user_id,
+            content={"membership": "leave"},
+        )
+
+        self._check_serialize_deserialize(event, context)
+
+    def _check_serialize_deserialize(self, event, context):
+        serialized = self.get_success(context.serialize(event, self.store))
+
+        d_context = EventContext.deserialize(self.storage, serialized)
+
+        self.assertEqual(context.state_group, d_context.state_group)
+        self.assertEqual(context.rejected, d_context.rejected)
+        self.assertEqual(
+            context.state_group_before_event, d_context.state_group_before_event
+        )
+        self.assertEqual(context.prev_group, d_context.prev_group)
+        self.assertEqual(context.delta_ids, d_context.delta_ids)
+        self.assertEqual(context.app_service, d_context.app_service)
+
+        self.assertEqual(
+            self.get_success(context.get_current_state_ids()),
+            self.get_success(d_context.get_current_state_ids()),
+        )
+        self.assertEqual(
+            self.get_success(context.get_prev_state_ids()),
+            self.get_success(d_context.get_prev_state_ids()),
+        )

tests/test_utils/event_injection.py

@@ -14,12 +14,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Optional
+from typing import Optional, Tuple
 
 import synapse.server
 from synapse.api.constants import EventTypes
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.events import EventBase
+from synapse.events.snapshot import EventContext
 from synapse.types import Collection
 
 from tests.test_utils import get_awaitable_result
@@ -75,6 +76,23 @@ def inject_event(
     """
     test_reactor = hs.get_reactor()
 
+    event, context = create_event(hs, room_version, prev_event_ids, **kwargs)
+
+    d = hs.get_storage().persistence.persist_event(event, context)
+    test_reactor.advance(0)
+    get_awaitable_result(d)
+
+    return event
+
+
+def create_event(
+    hs: synapse.server.HomeServer,
+    room_version: Optional[str] = None,
+    prev_event_ids: Optional[Collection[str]] = None,
+    **kwargs
+) -> Tuple[EventBase, EventContext]:
+    test_reactor = hs.get_reactor()
+
     if room_version is None:
         d = hs.get_datastore().get_room_version_id(kwargs["room_id"])
         test_reactor.advance(0)
@@ -89,8 +107,4 @@ def inject_event(
     test_reactor.advance(0)
     event, context = get_awaitable_result(d)
 
-    d = hs.get_storage().persistence.persist_event(event, context)
-    test_reactor.advance(0)
-    get_awaitable_result(d)
-
-    return event
+    return event, context