Make minor clarifications to the error messages given when we fail to join a room via any server.

changelog.d/13160.misc

@@ -0,0 +1 @@
+Make minor clarifications to the error messages given when we fail to join a room via any server.

synapse/federation/federation_client.py

@@ -686,6 +686,12 @@ async def _try_destination_list(
         if failover_errcodes is None:
             failover_errcodes = ()
 
+        if not destinations:
+            # Give a bit of a clearer message if no servers were specified at all.
+            raise SynapseError(
+                502, f"Failed to {description} via any server: No servers specified."
+            )
+
         for destination in destinations:
             if destination == self.server_name:
                 continue
@@ -735,7 +741,7 @@ async def _try_destination_list(
                     "Failed to %s via %s", description, destination, exc_info=True
                 )
 
-        raise SynapseError(502, "Failed to %s via any server" % (description,))
+        raise SynapseError(502, f"Failed to {description} via any server")
 
     async def make_membership_event(
         self,

synapse/handlers/room_member.py

@@ -1581,7 +1581,11 @@ async def _remote_join(
         ]
 
         if len(remote_room_hosts) == 0:
-            raise SynapseError(404, "No known servers")
+            raise SynapseError(
+                404,
+                "Can't join remote room because no servers "
+                "that are in the room have been provided.",
+            )
 
         check_complexity = self.hs.config.server.limit_remote_rooms.enabled
         if (