Show the position when an assertion fails

src/Nix/Exec.hs

@@ -77,7 +77,7 @@ type MonadNix e m =
      Typeable m, MonadVar m, MonadEffects m, MonadFix m, MonadCatch m,
      Alternative m)
 
-data ExecFrame m = Assertion (NValue m)
+data ExecFrame m = Assertion SrcSpan (NValue m)
     deriving (Show, Typeable)
 
 instance Typeable m => Frame (ExecFrame m)
@@ -189,13 +189,13 @@ instance MonadNix e m => MonadEval (NValue m) m where
             then addProvenance (\t -> Provenance scope (NIf_ span (Just c) (Just t) Nothing)) <$> t
             else addProvenance (\f -> Provenance scope (NIf_ span (Just c) Nothing (Just f))) <$> f
 
-    evalAssert c body = fromValue c >>= \b ->
+    evalAssert c body = fromValue c >>= \b -> do
+        span  <- currentPos
         if b
         then do
             scope <- currentScopes
-            span  <- currentPos
             addProvenance (\b -> Provenance scope (NAssert_ span (Just c) (Just b))) <$> body
-        else nverr $ Assertion c
+        else nverr $ Assertion span c
 
     evalApp f x = do
         scope <- currentScopes

src/Nix/Render.hs

@@ -1,6 +1,5 @@
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -27,11 +26,11 @@ posAndMsg beg msg =
 
 renderLocation :: MonadFile m => SrcSpan -> Doc -> m Doc
 renderLocation (SrcSpan beg@(SourcePos "<string>" _ _) _) msg =
-    return $ text $ parseErrorPretty @Char (posAndMsg beg msg)
+    return $ text $ init $ parseErrorPretty @Char (posAndMsg beg msg)
 
 renderLocation (SrcSpan beg@(SourcePos path _ _) _) msg = do
     contents <- Nix.Render.readFile path
-    return $ text $ parseErrorPretty' contents (posAndMsg beg msg)
+    return $ text $ init $ parseErrorPretty' contents (posAndMsg beg msg)
 
 {-
 -}

src/Nix/Render/Frame.hs

@@ -138,11 +138,12 @@ renderExecFrame :: (MonadReader e m, Has e Options, MonadVar m, MonadFile m)
 renderExecFrame _level f = do
     opts :: Options <- asks (view hasLens)
     (:[]) <$> case f of
-        Assertion v
+        Assertion ann v
             | values opts ->
-                  (text "Assertion failed:" </>) <$> renderNValueProv v
+                  renderLocation ann =<<
+                      ((text "Assertion failed:" </>) <$> renderNValueProv v)
             | otherwise ->
-                  pure $ text "Assertion failed"
+                  renderLocation ann (text "Assertion failed")
 
 renderThunkLoop :: (MonadReader e m, Has e Options, MonadFile m)
                 => NixLevel -> ThunkLoop -> m [Doc]