Fix error when sending message into deleted room. (#15235)

When a room is deleted in Synapse we remove the event forward
extremities in the room, so if (say a bot) tries to send a message into
the room we error out due to not being able to calculate prev events for
the new event *before* we check if the sender is in the room.

Fixes #8094

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py
index 9dbb778679..eb50086c50 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -402,6 +402,21 @@ class DeleteRoomTestCase(unittest.HomeserverTestCase):
         # Assert we can no longer peek into the room
         self._assert_peek(self.room_id, expect_code=403)
 
+    def test_room_delete_send(self) -> None:
+        """Test that sending into a deleted room returns a 403"""
+        channel = self.make_request(
+            "DELETE",
+            self.url,
+            content={},
+            access_token=self.admin_user_tok,
+        )
+
+        self.assertEqual(200, channel.code, msg=channel.json_body)
+
+        self.helper.send(
+            self.room_id, "test message", expect_code=403, tok=self.other_user_tok
+        )
+
     def _is_blocked(self, room_id: str, expect: bool = True) -> None:
         """Assert that the room is blocked or not"""
         d = self.store.is_room_blocked(room_id)