Take policy-configured max-priority into account

Part of #1590.

Author: michaelklishin

src/rabbit_amqqueue_process.erl

@@ -382,6 +382,7 @@ process_args_policy(State = #q{q                   = Q,
          {<<"message-ttl">>,             fun res_min/2, fun init_ttl/2},
          {<<"max-length">>,              fun res_min/2, fun init_max_length/2},
          {<<"max-length-bytes">>,        fun res_min/2, fun init_max_bytes/2},
+         {<<"max-priority">>,            fun res_arg/2, fun init_max_priority/2},
          {<<"overflow">>,                fun res_arg/2, fun init_overflow/2},
          {<<"queue-mode">>,              fun res_arg/2, fun init_queue_mode/2}],
       drop_expired_msgs(
@@ -426,6 +427,9 @@ init_max_bytes(MaxBytes, State) ->
     {_Dropped, State1} = maybe_drop_head(State#q{max_bytes = MaxBytes}),
     State1.
 
+init_max_priority(_MaxPriority, State) ->
+    State.
+
 init_overflow(undefined, State) ->
     State;
 init_overflow(Overflow, State) ->

src/rabbit_priority_queue.erl

@@ -28,6 +28,8 @@
                     {requires,    pre_boot},
                     {enables,     kernel_ready}]}).
 
+-import(rabbit_misc, [pget/2]).
+
 -export([enable/0]).
 
 -export([start/2, stop/1]).
@@ -43,6 +45,8 @@
          info/2, invoke/3, is_duplicate/2, set_queue_mode/2,
          zip_msgs_and_acks/4, handle_info/2]).
 
+-export([max_priority/1, priorities/1]).
+
 -record(state, {bq, bqss, max_priority}).
 -record(passthrough, {bq, bqs}).
 
@@ -125,9 +129,19 @@ collapse_recovery(QNames, DupNames, Recovery) ->
                               end, dict:new(), lists:zip(DupNames, Recovery)),
     [dict:fetch(Name, NameToTerms) || Name <- QNames].
 
-priorities(#amqqueue{arguments = Args}) ->
-    Ints = [long, short, signedint, byte, unsignedbyte, unsignedshort, unsignedint],
+max_priority(Q = #amqqueue{arguments = Args}) ->
     case rabbit_misc:table_lookup(Args, <<"x-max-priority">>) of
+        {Type, RequestedMax} -> {Type, RequestedMax};
+        undefined            ->
+            case rabbit_policy:effective_definition(Q) of
+                undefined -> undefined;
+                Proplist  -> {unsignedbyte, pget(<<"max-priority">>, Proplist)}
+            end
+    end.
+
+priorities(Q) ->
+    Ints = [long, short, signedint, byte, unsignedbyte, unsignedshort, unsignedint],
+    case max_priority(Q) of
         {Type, RequestedMax} ->
             case lists:member(Type, Ints) of
                 false -> none;