Pass leave from remote invite rejection down Sliding Sync (#18375)

Fixes #17753 


### Dev notes

The `sliding_sync_membership_snapshots` and `sliding_sync_joined_rooms`
database tables were added in
https://github.com/element-hq/synapse/pull/17512

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---------

Co-authored-by: Erik Johnston <erik@matrix.org>
Co-authored-by: Olivier 'reivilibre <oliverw@matrix.org>
Co-authored-by: Eric Eastwood <erice@element.io>

1 files changed, 58 insertions, 0 deletions

diff --git a/tests/rest/client/sliding_sync/test_sliding_sync.py b/tests/rest/client/sliding_sync/test_sliding_sync.py

index f3cf2111ec..dcec5b4cf0 100644
--- a/tests/rest/client/sliding_sync/test_sliding_sync.py
+++ b/tests/rest/client/sliding_sync/test_sliding_sync.py
@@ -790,6 +790,64 @@ class SlidingSyncTestCase(SlidingSyncBase):
             exact=True,
         )
 
+    def test_reject_remote_invite(self) -> None:
+        """Test that rejecting a remote invite comes down incremental sync"""
+
+        user_id = self.register_user("user1", "pass")
+        user_tok = self.login(user_id, "pass")
+
+        # Create a remote room invite (out-of-band membership)
+        room_id = "!room:remote.server"
+        self._create_remote_invite_room_for_user(user_id, None, room_id)
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [(EventTypes.Member, StateValues.ME)],
+                    "timeline_limit": 3,
+                }
+            }
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=user_tok)
+        # We should see the room (like normal)
+        self.assertIncludes(
+            set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+            {room_id},
+            exact=True,
+        )
+
+        # Reject the remote room invite
+        self.helper.leave(room_id, user_id, tok=user_tok)
+
+        # Sync again after rejecting the invite
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user_tok)
+
+        # The fix to add the leave event to incremental sync when rejecting a remote
+        # invite relies on the new tables to work.
+        if self.use_new_tables:
+            # We should see the newly_left room
+            self.assertIncludes(
+                set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+                {room_id},
+                exact=True,
+            )
+            # We should see the leave state for the room so clients don't end up with stuck
+            # invites
+            self.assertIncludes(
+                {
+                    (
+                        state["type"],
+                        state["state_key"],
+                        state["content"].get("membership"),
+                    )
+                    for state in response_body["rooms"][room_id]["required_state"]
+                },
+                {(EventTypes.Member, user_id, Membership.LEAVE)},
+                exact=True,
+            )
+
     def test_ignored_user_invites_initial_sync(self) -> None:
         """
         Make sure we ignore invites if they are from one of the `m.ignored_user_list` on