Fix #16392: revertCAFs in external interpreter when necessary

We revert CAFs when loading/adding modules in ghci (presumably to refresh
execution states and to allow for object code to be unloaded from the runtime).
However, with `-fexternal-interpreter` enabled, we are only doing it in the
ghci process instead of the external interpreter process where the cafs are
allocated and computed. This makes sure that revertCAFs is done in the
appropriate process no matter if that flag is present or not.

2 files changed, 9 insertions, 1 deletions

diff --git a/libraries/ghci/GHCi/Message.hs b/libraries/ghci/GHCi/Message.hs
index 959942e858..319eebdfc0 100644
--- a/libraries/ghci/GHCi/Message.hs
+++ b/libraries/ghci/GHCi/Message.hs
@@ -61,6 +61,7 @@ import System.IO.Error
 data Message a where
   -- | Exit the iserv process
   Shutdown :: Message ()
+  RtsRevertCAFs :: Message ()
 
   -- RTS Linker -------------------------------------------
 
@@ -485,7 +486,9 @@ getMessage = do
       33 -> Msg <$> (AddSptEntry <$> get <*> get)
       34 -> Msg <$> (RunTH <$> get <*> get <*> get <*> get)
       35 -> Msg <$> (GetClosure <$> get)
-      _  -> Msg <$> (Seq <$> get)
+      36 -> Msg <$> (Seq <$> get)
+      37 -> Msg <$> return RtsRevertCAFs
+      _  -> error $ "Unknown Message code " ++ (show b)
 
 putMessage :: Message a -> Put
 putMessage m = case m of
@@ -526,6 +529,7 @@ putMessage m = case m of
   RunTH st q loc ty           -> putWord8 34 >> put st >> put q >> put loc >> put ty
   GetClosure a                -> putWord8 35 >> put a
   Seq a                       -> putWord8 36 >> put a
+  RtsRevertCAFs               -> putWord8 37
 
 -- -----------------------------------------------------------------------------
 -- Reading/writing messages
diff --git a/libraries/ghci/GHCi/Run.hs b/libraries/ghci/GHCi/Run.hs
index 72099b205f..a931e620cc 100644
--- a/libraries/ghci/GHCi/Run.hs
+++ b/libraries/ghci/GHCi/Run.hs
@@ -44,9 +44,13 @@ import Unsafe.Coerce
 -- -----------------------------------------------------------------------------
 -- Implement messages
 
+foreign import ccall "revertCAFs" rts_revertCAFs  :: IO ()
+        -- Make it "safe", just in case
+
 run :: Message a -> IO a
 run m = case m of
   InitLinker -> initObjLinker RetainCAFs
+  RtsRevertCAFs -> rts_revertCAFs
   LookupSymbol str -> fmap toRemotePtr <$> lookupSymbol str
   LookupClosure str -> lookupClosure str
   LoadDLL str -> loadDLL str