More graceful failure

`error` is simply wrong in `IO`-ish contexts. Use fail or throwIO.

hs-bindgen/src/HsBindgen/C/Fold/Type.hs

@@ -374,11 +374,11 @@ mkStructField unit path current = do
           tokens <- HighLevel.clang_tokenize unit (multiLocExpansion <$> extent)
           case reparseWith reparseFieldDecl tokens of
             Left err ->
-              error $ "mkStructField: " ++ show err
+              fail $ "mkStructField: " ++ show err
             Right (fieldType, fieldName) -> do
               fieldOffset <- fromIntegral <$> clang_Cursor_getOffsetOfField current
               unless (fieldOffset `mod` 8 == 0) $
-                error "bit-fields not supported yet"
+                fail "bit-fields not supported yet"
               return $ Just StructField{fieldName, fieldOffset, fieldType}
 
         else do
@@ -388,7 +388,7 @@ mkStructField unit path current = do
           fieldType   <- processTypeDeclRec (PathField fieldName path) unit ty
           fieldOffset <- fromIntegral <$> liftIO (clang_Cursor_getOffsetOfField current)
 
-          unless (fieldOffset `mod` 8 == 0) $ error "bit-fields not supported yet"
+          unless (fieldOffset `mod` 8 == 0) $ fail "bit-fields not supported yet"
 
           return $ Just StructField{fieldName, fieldOffset, fieldType}
 

hs-bindgen/src/HsBindgen/Eff.hs

@@ -24,7 +24,7 @@ import HsBindgen.Imports
 newtype Eff m a = Eff {
       getEff :: ReaderT (Support m) IO a
     }
-  deriving newtype (Functor, Applicative, Monad, MonadIO, MonadUnliftIO)
+  deriving newtype (Functor, Applicative, Monad, MonadFail, MonadIO, MonadUnliftIO)
 
 wrapEff :: (Support m -> IO a) -> Eff m a
 wrapEff = Eff . ReaderT

hs-bindgen/tests/TastyGolden.hs

@@ -79,6 +79,8 @@ runGoldenSteps (GoldenSteps getGolden getTested cmp update) progress opts = do
     mbNew <- try $ getTested stepFn
     msgs <- readIORef msgsRef <&> reverse
 
+    print $ either (const 'x') (const 'y') mbNew
+
     case mbNew of
         Left e
             | Just _ <- fromException @AsyncException e -> throwIO e