issue #14: fix crash when creating deduplicating and priority queue

The priority queue behaviour implementation makes assumptions on the
format of the returned information.

Therefore, appending additional information to the returned one will
cause priority queues to crash.

This patch prevents returning the cache status when priority queues
are enabled.

Signed-off-by: Matteo Cafasso <[email protected]>

Author: noxdafox

lib/rabbit_message_deduplication_queue.ex

@@ -329,9 +329,11 @@ defmodule RabbitMQ.MessageDeduplicationPlugin.Queue do
   end
 
   def info(:backing_queue_status, dqstate(queue: queue, queue_state: qs)) do
+    amqqueue(arguments: args) = queue
     queue_info = passthrough do: info(:backing_queue_status, qs)
+    priority = Common.rabbit_argument(args, "x-max-priority", default: false)
 
-    if duplicate?(queue) do
+    if duplicate?(queue) and !priority do
       [message_deduplication_cache_info: cache_info(queue)] ++ queue_info
     else
       queue_info