Add streaming support to GHC debug brick

This is accomplished by a new tracing module GHC.Debug.StreamedTrace that is able to produce results incrementally.

client/src/GHC/Debug/Retainers.hs

@@ -24,14 +24,12 @@ import Control.Monad.State
 import GHC.Debug.Trace
 import GHC.Debug.Types.Graph
 import Control.Monad
+import GHC.Debug.StreamedTrace
 
 import qualified Data.Set as Set
 import Control.Monad.RWS
 import Data.Word
-
-addOne :: a -> (Maybe Int, [a]) -> (Maybe Int, [a])
-addOne _ (Just 0, cp) = (Just 0, cp)
-addOne cp (n, cps)    = (subtract 1 <$> n, cp : cps)
+import Data.List.NonEmpty ( NonEmpty(..) )
 
 data EraRange
   = EraRange { startEra :: Word64, endEra :: Word64} -- inclusive
@@ -100,27 +98,27 @@ matchesFilter filter ptr sc parents = case filter of
 findRetainersOf :: Maybe Int
                 -> [ClosurePtr]
                 -> [ClosurePtr]
-                -> DebugM [[ClosurePtr]]
+                -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOf limit cps bads =
   findRetainers limit (AddressFilter (`Set.member` bad_set)) cps
   where
     bad_set = Set.fromList bads
 
 findRetainersOfConstructor :: Maybe Int
-                           -> [ClosurePtr] -> String -> DebugM [[ClosurePtr]]
+                           -> [ClosurePtr] -> String -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOfConstructor limit rroots con_name =
   findRetainers limit (ConstructorDescFilter ((== con_name) . name)) rroots
 
 findRetainersOfConstructorExact
   :: Maybe Int
-  -> [ClosurePtr] -> String -> DebugM [[ClosurePtr]]
+  -> [ClosurePtr] -> String -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOfConstructorExact limit rroots clos_name =
   findRetainers limit (InfoSourceFilter ((== clos_name) . infoName)) rroots
 
 findRetainersOfEra
   :: Maybe Int
   -> EraRange
-  -> [ClosurePtr] -> DebugM [[ClosurePtr]]
+  -> [ClosurePtr] -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOfEra limit eras rroots =
   findRetainers limit filter rroots
   where
@@ -128,7 +126,7 @@ findRetainersOfEra limit eras rroots =
 
 findRetainersOfArrWords
   :: Maybe Int
-  -> [ClosurePtr] -> Size -> DebugM [[ClosurePtr]]
+  -> [ClosurePtr] -> Size -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOfArrWords limit rroots lim =
   findRetainers limit filter rroots
   where
@@ -138,7 +136,7 @@ findRetainersOfArrWords limit rroots lim =
 
 findRetainersOfInfoTable
   :: Maybe Int
-  -> [ClosurePtr] -> InfoTablePtr -> DebugM [[ClosurePtr]]
+  -> [ClosurePtr] -> InfoTablePtr -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
 findRetainersOfInfoTable limit rroots info_ptr =
   findRetainers limit (InfoPtrFilter (== info_ptr)) rroots
 
@@ -148,28 +146,26 @@ findRetainersOfInfoTable limit rroots info_ptr =
 -- such as 10.
 findRetainers :: Maybe Int
   -> ClosureFilter
-  -> [ClosurePtr] -> DebugM [[ClosurePtr]]
-findRetainers limit filter rroots = (\(_, r, _) -> snd r) <$> runRWST (traceFromM funcs rroots) [] (limit, [])
+  -> [ClosurePtr] -> DebugM (ResultStream (NonEmpty ClosurePtr) () (Maybe ()))
+findRetainers limit filter rroots = traceStreamResults rroots limit [] funcs
   where
-    funcs = justClosures closAccum
+    funcs = justStreamClosures closAccum
     -- Add clos
     closAccum  :: ClosurePtr
                -> SizedClosure
-               -> RWST [ClosurePtr] () (Maybe Int, [[ClosurePtr]]) DebugM ()
-               -> RWST [ClosurePtr] () (Maybe Int, [[ClosurePtr]]) DebugM ()
-    closAccum _ (noSize -> WeakClosure {}) _ = return ()
-    closAccum cp sc k = do
-      ctx <- ask
-      b <- lift $ matchesFilter filter cp sc ctx
-      if b
-      then do
-        modify' (addOne (cp: ctx))
-        local (cp:) k
-      else do
-        (lim, _) <- get
-        case lim of
-          Just 0 -> return ()
-          _ -> local (cp:) k
+               -> Maybe Int
+               -> [ClosurePtr]
+               -> DebugM (Step (Maybe Int) [ClosurePtr] (NonEmpty ClosurePtr) ())
+    closAccum _ (noSize -> WeakClosure {}) l _ = return $ Step Nothing (Prune l)
+    closAccum cp sc remaining ctx
+      | Just r <- remaining
+      , r <= 0 = return $ Step Nothing (End ())
+      | otherwise = do
+        b <- matchesFilter filter cp sc ctx
+        let next = Continue (if b then (subtract 1 <$> remaining) else remaining) (cp:ctx)
+        if b
+        then return $ Step (Just (cp:|ctx))  next
+        else return $ Step Nothing next
 
 addLocationToStack :: [ClosurePtr] -> DebugM [(SizedClosureP, Maybe SourceInformation)]
 addLocationToStack r = do