Move MonadAtomicRef ST instance to Nix.Thunk

src/Nix/Thunk.hs

@@ -26,6 +26,7 @@ import Control.Monad.Except
 import Control.Monad.Reader
 import Control.Monad.Ref
 import Control.Monad.State
+import Control.Monad.ST
 import Control.Monad.Writer
 import Data.GADT.Compare
 import Data.IORef
@@ -37,6 +38,19 @@ import Unsafe.Coerce
 
 import Nix.Utils
 
+-- Since there's no forking, it's automatically atomic.
+instance MonadAtomicRef (ST s) where
+  atomicModifyRef r f = do
+    v <- readRef r
+    let (a, b) = f v
+    writeRef r a
+    return b
+  atomicModifyRef' r f = do
+    v <- readRef r
+    let (a, b) = f v
+    writeRef r $! a
+    return b
+
 data Deferred m v = Deferred (m v) | Computed v
     deriving (Functor, Foldable, Traversable)
 

src/Nix/Type/Infer.hs

@@ -13,7 +13,7 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeSynonymInstances #-}
 
-{-# OPTIONS_GHC -Wno-name-shadowing -Wno-orphans #-}
+{-# OPTIONS_GHC -Wno-name-shadowing #-}
 
 module Nix.Type.Infer (
   Constraint(..),
@@ -186,19 +186,6 @@ instance Monoid InferError where
 -- Inference
 -------------------------------------------------------------------------------
 
--- Since there's no forking, it's automatically atomic.
-instance MonadAtomicRef (ST s) where
-  atomicModifyRef r f = do
-    v <- readRef r
-    let (a, b) = f v
-    writeRef r a
-    return b
-  atomicModifyRef' r f = do
-    v <- readRef r
-    let (a, b) = f v
-    writeRef r $! a
-    return b
-
 -- | Run the inference monad
 runInfer' ::
   ( MonadFreshId Int m