Fix bug which caused rejected events to be stored with the wrong room state (#6320)

Fixes a bug where rejected events were persisted with the wrong state group.

Also fixes an occasional internal-server-error when receiving events over
federation which are rejected and (possibly because they are
backwards-extremities) have no prev_group.

Fixes #6289.

1 files changed, 50 insertions, 11 deletions

diff --git a/tests/test_state.py b/tests/test_state.py
index 38246555bd..176535947a 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -21,6 +21,7 @@ from synapse.api.auth import Auth
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.room_versions import RoomVersions
 from synapse.events import FrozenEvent
+from synapse.events.snapshot import EventContext
 from synapse.state import StateHandler, StateResolutionHandler
 
 from tests import unittest
@@ -198,16 +199,22 @@ class StateTestCase(unittest.TestCase):
 
         self.store.register_events(graph.walk())
 
-        context_store = {}
+        context_store = {}  # type: dict[str, EventContext]
 
         for event in graph.walk():
             context = yield self.state.compute_event_context(event)
             self.store.register_event_context(event, context)
             context_store[event.event_id] = context
 
-        prev_state_ids = yield context_store["D"].get_prev_state_ids(self.store)
+        ctx_c = context_store["C"]
+        ctx_d = context_store["D"]
+
+        prev_state_ids = yield ctx_d.get_prev_state_ids(self.store)
         self.assertEqual(2, len(prev_state_ids))
 
+        self.assertEqual(ctx_c.state_group, ctx_d.state_group_before_event)
+        self.assertEqual(ctx_d.state_group_before_event, ctx_d.state_group)
+
     @defer.inlineCallbacks
     def test_branch_basic_conflict(self):
         graph = Graph(
@@ -241,12 +248,19 @@ class StateTestCase(unittest.TestCase):
             self.store.register_event_context(event, context)
             context_store[event.event_id] = context
 
-        prev_state_ids = yield context_store["D"].get_prev_state_ids(self.store)
+        # C ends up winning the resolution between B and C
+
+        ctx_c = context_store["C"]
+        ctx_d = context_store["D"]
 
+        prev_state_ids = yield ctx_d.get_prev_state_ids(self.store)
         self.assertSetEqual(
             {"START", "A", "C"}, {e_id for e_id in prev_state_ids.values()}
         )
 
+        self.assertEqual(ctx_c.state_group, ctx_d.state_group_before_event)
+        self.assertEqual(ctx_d.state_group_before_event, ctx_d.state_group)
+
     @defer.inlineCallbacks
     def test_branch_have_banned_conflict(self):
         graph = Graph(
@@ -292,11 +306,18 @@ class StateTestCase(unittest.TestCase):
             self.store.register_event_context(event, context)
             context_store[event.event_id] = context
 
-        prev_state_ids = yield context_store["E"].get_prev_state_ids(self.store)
+        # C ends up winning the resolution between C and D because bans win over other
+        # changes
+
+        ctx_c = context_store["C"]
+        ctx_e = context_store["E"]
 
+        prev_state_ids = yield ctx_e.get_prev_state_ids(self.store)
         self.assertSetEqual(
             {"START", "A", "B", "C"}, {e for e in prev_state_ids.values()}
         )
+        self.assertEqual(ctx_c.state_group, ctx_e.state_group_before_event)
+        self.assertEqual(ctx_e.state_group_before_event, ctx_e.state_group)
 
     @defer.inlineCallbacks
     def test_branch_have_perms_conflict(self):
@@ -360,12 +381,20 @@ class StateTestCase(unittest.TestCase):
             self.store.register_event_context(event, context)
             context_store[event.event_id] = context
 
-        prev_state_ids = yield context_store["D"].get_prev_state_ids(self.store)
+        # B ends up winning the resolution between B and C because power levels
+        # win over other changes.
 
+        ctx_b = context_store["B"]
+        ctx_d = context_store["D"]
+
+        prev_state_ids = yield ctx_d.get_prev_state_ids(self.store)
         self.assertSetEqual(
             {"A1", "A2", "A3", "A5", "B"}, {e for e in prev_state_ids.values()}
         )
 
+        self.assertEqual(ctx_b.state_group, ctx_d.state_group_before_event)
+        self.assertEqual(ctx_d.state_group_before_event, ctx_d.state_group)
+
     def _add_depths(self, nodes, edges):
         def _get_depth(ev):
             node = nodes[ev]
@@ -390,13 +419,16 @@ class StateTestCase(unittest.TestCase):
 
         context = yield self.state.compute_event_context(event, old_state=old_state)
 
-        current_state_ids = yield context.get_current_state_ids(self.store)
+        prev_state_ids = yield context.get_prev_state_ids(self.store)
+        self.assertCountEqual((e.event_id for e in old_state), prev_state_ids.values())
 
-        self.assertEqual(
-            set(e.event_id for e in old_state), set(current_state_ids.values())
+        current_state_ids = yield context.get_current_state_ids(self.store)
+        self.assertCountEqual(
+            (e.event_id for e in old_state), current_state_ids.values()
         )
 
-        self.assertIsNotNone(context.state_group)
+        self.assertIsNotNone(context.state_group_before_event)
+        self.assertEqual(context.state_group_before_event, context.state_group)
 
     @defer.inlineCallbacks
     def test_annotate_with_old_state(self):
@@ -411,11 +443,18 @@ class StateTestCase(unittest.TestCase):
         context = yield self.state.compute_event_context(event, old_state=old_state)
 
         prev_state_ids = yield context.get_prev_state_ids(self.store)
+        self.assertCountEqual((e.event_id for e in old_state), prev_state_ids.values())
 
-        self.assertEqual(
-            set(e.event_id for e in old_state), set(prev_state_ids.values())
+        current_state_ids = yield context.get_current_state_ids(self.store)
+        self.assertCountEqual(
+            (e.event_id for e in old_state + [event]), current_state_ids.values()
         )
 
+        self.assertIsNotNone(context.state_group_before_event)
+        self.assertNotEqual(context.state_group_before_event, context.state_group)
+        self.assertEqual(context.state_group_before_event, context.prev_group)
+        self.assertEqual({("state", ""): event.event_id}, context.delta_ids)
+
     @defer.inlineCallbacks
     def test_trivial_annotate_message(self):
         prev_event_id = "prev_event_id"