Amqpx.Queue.message_count

You're seeing just the function message_count, go back to Amqpx.Queue module for more information.
Link to this function

message_count(channel, queue)

Specs

message_count(Amqpx.Channel.t(), Amqpx.Basic.queue()) :: integer() | no_return()

Returns the number of messages that are ready for delivery (e.g. not pending acknowledgements) in the queue.