GhcPlugins: Fix lookup of TH names

Previously `thNameToGhcName` was calling `lookupOrigNameCache` directly, which
failed to handle the case that the name wasn't already in the name cache. This
happens, for instance, when the name was in scope in a plugin being used during
compilation but not in scope in the module being compiled. In this case we the
interface file containing the name won't be loaded and `lookupOrigNameCache`
fails. This was the cause of #16104.

The solution is simple: use the nicely packaged `lookupOrigIO` instead.

(cherry picked from commit 0d9f105ba423af4f2ca215a18d04d4c8e2c372a8)

1 files changed, 3 insertions, 2 deletions

diff --git a/compiler/simplCore/CoreMonad.hs b/compiler/simplCore/CoreMonad.hs
index 912ff9949c..683fb0434d 100644
--- a/compiler/simplCore/CoreMonad.hs
+++ b/compiler/simplCore/CoreMonad.hs
@@ -67,6 +67,7 @@ import Annotations
 
 import IOEnv hiding     ( liftIO, failM, failWithM )
 import qualified IOEnv  ( liftIO )
+import IfaceEnv         ( lookupOrigIO )
 import TcEnv            ( lookupGlobal )
 import Var
 import Outputable
@@ -821,6 +822,6 @@ thNameToGhcName th_name
       | Just n <- isExact_maybe rdr_name   -- This happens in derived code
       = return $ if isExternalName n then Just n else Nothing
       | Just (rdr_mod, rdr_occ) <- isOrig_maybe rdr_name
-      = do { cache <- getOrigNameCache
-           ; return $ lookupOrigNameCache cache rdr_mod rdr_occ }
+      = do { hsc_env <- getHscEnv
+           ; Just <$> liftIO (lookupOrigIO hsc_env rdr_mod rdr_occ) }
       | otherwise = return Nothing