Merge pull request #308 from basho/gh267-2.x

Backport fix from #306 into 2.x branch

Reviewed-by: macintux

src/lager.erl

@@ -210,7 +210,16 @@ stop_trace(Backend, Filter, Level) ->
 stop_trace({Backend, Filter, Level}) ->
     stop_trace(Backend, Filter, Level).
 
-stop_trace_int({Backend, _Filter, _Level} = Trace) ->
+%% Important: validate_trace_filters orders the arguments of
+%% trace tuples differently than the way outside callers have
+%% the trace tuple.
+%%
+%% That is to say, outside they are represented as 
+%% `{Backend, Filter, Level}'
+%%
+%% and when they come back from validation, they're
+%% `{Filter, Level, Backend}'
+stop_trace_int({_Filter, _Level, Backend} = Trace) ->
     {Level, Traces} = lager_config:get(loglevel),
     NewTraces =  lists:delete(Trace, Traces),
     _ = lager_util:trace_filter([ element(1, T) || T <- NewTraces ]),

test/lager_test_backend.erl

@@ -489,6 +489,24 @@ lager_test_() ->
                         ok
                 end
             },
+            {"stopped trace stops and removes its event handler (gh#267)",
+                fun() ->
+                        StartHandlers = gen_event:which_handlers(lager_event),
+                        {_, T0} = lager_config:get(loglevel),
+                        ?assertEqual([], T0),
+                        {ok, Test} = lager:trace_file("/tmp/test", [{vhost, test}]),
+                        MidHandlers = gen_event:which_handlers(lager_event),
+                        ?assertEqual(length(StartHandlers)+1, length(MidHandlers)),
+                        {_, T1} = lager_config:get(loglevel),
+                        ?assertEqual(1, length(T1)),
+                        ok = lager:stop_trace(Test),
+                        {_, T2} = lager_config:get(loglevel),
+                        ?assertEqual([], T2),
+                        EndHandlers = gen_event:which_handlers(lager_event),
+                        ?assertEqual(StartHandlers, EndHandlers),
+                        ok
+                end
+            },
             {"record printing works",
                 fun() ->
                         print_state(),