Fix MonadFreshId instances in wrong places

src/Nix/Exec.hs

@@ -84,7 +84,7 @@ import           GHC.DataSize
 type MonadNix e m =
     (Scoped (NThunk m) m, Framed e m, Has e SrcSpan, Has e Options,
      Typeable m, MonadVar m, MonadEffects m, MonadFix m, MonadCatch m,
-     Alternative m)
+     Alternative m, MonadFreshId Int m)
 
 data ExecFrame m = Assertion SrcSpan (NValue m)
     deriving (Show, Typeable)
@@ -489,7 +489,7 @@ newtype Lazy m a = Lazy
     { runLazy :: ReaderT (Context (Lazy m) (NThunk (Lazy m)))
                         (StateT (HashMap FilePath NExprLoc) (FreshIdT Int m)) a }
     deriving (Functor, Applicative, Alternative, Monad, MonadPlus,
-              MonadFix, MonadIO, MonadFreshId Int,
+              MonadFix, MonadIO,
               MonadReader (Context (Lazy m) (NThunk (Lazy m))))
 
 instance MonadTrans Lazy where
@@ -520,6 +520,9 @@ instance MonadException m => MonadException (Lazy m) where
       in runLazy <$> f run'
 #endif
 
+instance Monad m => MonadFreshId Int (Lazy m) where
+  freshId = Lazy $ lift $ lift freshId
+
 instance MonadStore m => MonadStore (Lazy m) where
     addPath' = lift . addPath'
     toFile_' n = lift . toFile_' n

src/Nix/Lint.hs

@@ -117,7 +117,7 @@ unpackSymbolic :: MonadVar m
 unpackSymbolic = readVar . coerce
 
 type MonadLint e m = (Scoped (SThunk m) m, Framed e m, MonadVar m,
-                      MonadCatch m)
+                      MonadCatch m, MonadFreshId Int m)
 
 symerr :: forall e m a. MonadLint e m => String -> m a
 symerr = evalError @(Symbolic m) . ErrorCall

src/Nix/Thunk.hs

@@ -100,7 +100,6 @@ instance MonadFreshId i m => MonadFreshId i (StateT s m)
 type MonadVar m =
   ( MonadAtomicRef m
   , GEq (Ref m)
-  , MonadFreshId Int m
   )
 
 eqVar :: forall m a. GEq (Ref m) => Ref m a -> Ref m a -> Bool
@@ -146,7 +145,7 @@ instance Exception ThunkLoop
 valueRef :: v -> Thunk m v
 valueRef = Value
 
-buildThunk :: MonadVar m => m v -> m (Thunk m v)
+buildThunk :: (MonadVar m, MonadFreshId Int m) => m v -> m (Thunk m v)
 buildThunk action =do
     freshThunkId <- freshId
     Thunk freshThunkId <$> newVar False <*> newVar (Deferred action)