amqqueue_process: adopt new is_duplicate backing queue callback

As the de-duplication plugin is the only adopter of the `is_duplicate`
callback, we now use a simpler signature.

When a message is deemed duplicated, we discard it and re-route it to
dead letter exchange.

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

Author: noxdafox

deps/rabbit/src/rabbit_amqqueue_process.erl

@@ -722,8 +722,10 @@ maybe_deliver_or_enqueue(Delivery = #delivery{message = Message},
             %% Drop publish and nack to publisher
             send_reject_publish(Delivery, State);
         _ ->
-            case BQ:is_duplicate(Message, BQS) of
-                {true, State1} ->
+            {IsDuplicate, BQS1} = BQ:is_duplicate(Message, BQS),
+            State1 = State#q{backing_queue_state = BQS1},
+            case IsDuplicate of
+                true ->
                     %% Publish to DLX
                     _ = with_dlx(
                           DLX,
@@ -741,8 +743,8 @@ maybe_deliver_or_enqueue(Delivery = #delivery{message = Message},
                           end),
                     %% Drop publish and nack to publisher
                     send_reject_publish(Delivery, State1);
-                %% Enqueue and maybe drop head later
-                {false, State1} ->
+                false ->
+                    %% Enqueue and maybe drop head later
                     deliver_or_enqueue(Delivery, Delivered, State1)
             end
     end.