[fix] add bang pattern to lookupKeyValue to avoid reordering with newKey

Author: MangoIV

hls-graph/src/Development/IDE/Graph/Internal/Key.hs

@@ -83,8 +83,15 @@ newKey k = unsafePerformIO $ do
             in (GlobalKeyValueMap (Map.insert newKey new_index hm) (IM.insert n newKey im) (n+1), new_index)
 {-# NOINLINE newKey #-}
 
+-- NOTE:
+-- The argument to this function has a bang pattern. This bang pattern is a load
+-- bearing bang pattern. The reason is that the x, if not forced yet, is a thunk
+-- that forces the atomicModifyIORef' in the creation of the new key. If it
+-- isn't forced *before* reading the keyMap, the keyMap will only obtain the new
+-- key (x) *after* the IntMap is already copied out of the keyMap reference,
+-- i.e. when it is forced for the lookup in the IntMap.
 lookupKeyValue :: Key -> KeyValue
-lookupKeyValue (UnsafeMkKey x) = unsafePerformIO $ do
+lookupKeyValue (UnsafeMkKey !x) = unsafePerformIO $ do
   GlobalKeyValueMap _ im _ <- readIORef keyMap
   pure $! im IM.! x