Fix mango native proc crash (#1067)

Don't crash on receiving cast stop

When soft limit is reached couch_proc_manager
evicts idle processes by casting on them `stop`
message. Since mango_native_proc doesn't handle
this message it results to its crash with
`invalid_cast` reason.

2 files changed, 36 insertions, 2 deletions

diff --git a/src/mango/src/mango_idx_text.erl b/src/mango/src/mango_idx_text.erl
index 369e2cd08..29b4441a1 100644
--- a/src/mango/src/mango_idx_text.erl
+++ b/src/mango/src/mango_idx_text.erl
@@ -330,7 +330,7 @@ indexable_fields(Fields, {op_not, {ExistsQuery, Arg}}) when is_tuple(Arg) ->
     Fields0 = indexable_fields(Fields, ExistsQuery),
     indexable_fields(Fields0, Arg);
 % forces "$exists" : false to use _all_docs
-indexable_fields(Fields, {op_not, {ExistsQuery, false}}) ->
+indexable_fields(_, {op_not, {_, false}}) ->
     [];
 
 indexable_fields(Fields, {op_insert, Arg}) when is_binary(Arg) ->
diff --git a/src/mango/src/mango_native_proc.erl b/src/mango/src/mango_native_proc.erl
index 61d79b7ec..7a3420193 100644
--- a/src/mango/src/mango_native_proc.erl
+++ b/src/mango/src/mango_native_proc.erl
@@ -113,6 +113,9 @@ handle_cast(garbage_collect, St) ->
     erlang:garbage_collect(),
     {noreply, St};
 
+handle_cast(stop, St) ->
+    {stop, normal, St};
+
 handle_cast(Msg, St) ->
     {stop, {invalid_cast, Msg}, St}.
 
@@ -363,4 +366,35 @@ validate_index_info(IndexInfo) ->
             [invalid_index | Results0]
         end
     end, [], IdxTypes),
-    lists:member(valid_index, Results).
\ No newline at end of file
+    lists:member(valid_index, Results).
+
+
+-ifdef(TEST).
+
+-include_lib("eunit/include/eunit.hrl").
+
+handle_garbage_collect_cast_test() ->
+    Pid = self(),
+    {_, TracerRef} = spawn_monitor(fun() ->
+        erlang:trace(Pid, true, [garbage_collection]),
+        receive {trace, Pid, gc_start, _} ->
+            erlang:trace(Pid, false, [garbage_collection]),
+            exit(gc_start)
+        end
+    end),
+    erlang:yield(),
+    ?assertEqual({noreply, []}, handle_cast(garbage_collect, [])),
+    receive
+        {'DOWN', TracerRef, _, _, Msg} -> ?assertEqual(gc_start, Msg)
+    after 1000 ->
+        erlang:error({assertion_failed, [{module, ?MODULE}, {line, ?LINE},
+            {expected, gc_start}, {reason, timeout}]})
+    end.
+
+handle_stop_cast_test() ->
+    ?assertEqual({stop, normal, []}, handle_cast(stop, [])).
+
+handle_invalid_cast_test() ->
+    ?assertEqual({stop, {invalid_cast, random}, []}, handle_cast(random, [])).
+
+-endif.