Add a Calling info frame

src/Nix/Eval.hs

@@ -99,6 +99,7 @@ type MonadNixEval e v t m =
 data EvalFrame m v
     = EvaluatingExpr (Scopes m v) NExprLoc
     | ForcingExpr (Scopes m v) NExprLoc
+    | Calling String SrcSpan
     deriving (Show, Typeable)
 
 instance (Typeable m, Typeable v) => Exception (EvalFrame m v)

src/Nix/Exec.hs

@@ -243,14 +243,15 @@ instance MonadNix e m => MonadEval (NValue m) m where
     evalError = throwError
 
 infixl 1 `callFunc`
-callFunc :: MonadNix e m => NValue m -> m (NValue m) -> m (NValue m)
+callFunc :: forall e m. (MonadNix e m, Typeable m)
+         => NValue m -> m (NValue m) -> m (NValue m)
 callFunc fun arg = case fun of
     NVClosure params f -> do
         traceM $ "callFunc:NVFunction taking " ++ show params
         f arg
     NVBuiltin name f -> do
-        traceM $ "callFunc:NVBuiltin " ++ name
-        f arg
+        span <- currentPos
+        withFrame Info (Calling @m @(NThunk m) name span) $ f arg
     s@(NVSet m _) | Just f <- M.lookup "__functor" m -> do
         traceM "callFunc:__functor"
         force f $ (`callFunc` pure s) >=> (`callFunc` arg)

src/Nix/Render/Frame.hs

@@ -98,6 +98,11 @@ renderEvalFrame level f = do
                   fmap (:[]) $ renderLocation ann
                       =<< renderExpr level "While forcing thunk from"
                                      "Forcing thunk" e
+
+        Calling name ann ->
+            fmap (:[]) $ renderLocation ann $
+                text "While calling builtins." <> text name
+
         _ -> pure []
 
 renderExpr :: (MonadReader e m, Has e Options, MonadFile m)