added test case for dbg opt pred_has_facts

Summary: Added a test case for prev diffs in stack, to ensure we get warnings in ``` userQueryResults_diagnostics``` when ``` queryDebugOptions_pred_has_facts = True``` , if db has no facts of the predicate

Reviewed By: josefs

Differential Revision: D65818386

fbshipit-source-id: deed56aada2e77fbf0a38152b7605f8d3125090e

glean/hs/Glean/Query/Thrift/Internal.hs

@@ -32,6 +32,7 @@ module Glean.Query.Thrift.Internal
   , displayQuery
   , decodeResults
   , justCheck
+  , dbgPredHasFacts
   ) where
 
 import Control.Exception
@@ -222,6 +223,12 @@ justCheck (Query q) = Query q'
   q' = q { userQuery_options = Just (fromMaybe def (userQuery_options q))
   { userQueryOptions_just_check = True } }
 
+dbgPredHasFacts :: Query a -> Query a
+dbgPredHasFacts (Query q) = Query q'
+  where
+  q' = q { userQuery_options = Just (fromMaybe def (userQuery_options q))
+  { userQueryOptions_debug = def {queryDebugOptions_pred_has_facts = True}}}
+
 reportUserQueryStats :: Thrift.UserQueryStats -> IO ()
 reportUserQueryStats stats =
   vlog 1 $ showUserQueryStats stats