Function queue_args 

pub fn queue_args(config: &QueueConfig) -> FieldTable

Declaration arguments for the main queue q.

• x-message-ttl when QueueConfig::message_ttl is set (in whole milliseconds, rounded up, at least 1).
• x-max-priority when QueueConfig::max_priority is Some, so deferred jobs can come back ahead of the backlog.

Both are declaration arguments, which RabbitMQ refuses to change on an existing queue (PRECONDITION_FAILED, which closes the declaring channel). Adding x-max-priority to a queue that predates this feature therefore requires deleting the queue or setting max_priority = 0.