From bd9821f7f17916deec9266483e26b69cd5ce2b3b Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Tue, 4 Jan 2022 16:10:05 +0000
Subject: Better error messages from `get_create_event_for_room` (#11638)

"Unknown room" can mean a multitude of things here. To help with debugging, add
some more words to the exception text.
---
 changelog.d/11638.misc                  | 1 +
 synapse/storage/databases/main/state.py | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/11638.misc

diff --git a/changelog.d/11638.misc b/changelog.d/11638.misc
new file mode 100644
index 0000000000..76dfb56bda
--- /dev/null
+++ b/changelog.d/11638.misc
@@ -0,0 +1 @@
+Improve the error messages from  `get_create_event_for_room`.
diff --git a/synapse/storage/databases/main/state.py b/synapse/storage/databases/main/state.py
index 7e5a6aae18..2fb3e65192 100644
--- a/synapse/storage/databases/main/state.py
+++ b/synapse/storage/databases/main/state.py
@@ -177,11 +177,15 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
             NotFoundError if the room is unknown
         """
         state_ids = await self.get_current_state_ids(room_id)
+
+        if not state_ids:
+            raise NotFoundError(f"Current state for room {room_id} is empty")
+
         create_id = state_ids.get((EventTypes.Create, ""))
 
         # If we can't find the create event, assume we've hit a dead end
         if not create_id:
-            raise NotFoundError("Unknown room %s" % (room_id,))
+            raise NotFoundError(f"No create event in current state for room {room_id}")
 
         # Retrieve the room's create event and return
         create_event = await self.get_event(create_id)
-- 
cgit 1.4.1