Give readProcess' more sensible error messages.

Also a bunch of refactoring for GhcModError

Language/Haskell/GhcMod/Utils.hs

@@ -1,12 +1,10 @@
 module Language.Haskell.GhcMod.Utils where
 
 
-import Control.Exception
-import Control.Monad.Error (MonadError(..), Error(..))
+import Language.Haskell.GhcMod.Error
 import MonadUtils (MonadIO, liftIO)
 import System.Directory (getCurrentDirectory, setCurrentDirectory)
 import System.Exit (ExitCode(..))
-import System.IO.Error (tryIOError)
 import System.Process (readProcessWithExitCode)
 
 -- dropWhileEnd is not provided prior to base 4.5.0.0.
@@ -25,39 +23,22 @@ extractParens str = extractParens' str 0
        | s `elem` "}])" = s : extractParens' ss (level-1)
        | otherwise = s : extractParens' ss level
 
-readProcess' :: (MonadIO m, Error e, MonadError e m)
+readProcess' :: (MonadIO m, MonadError GhcModError m)
              => String
              -> [String]
              -> m String
 readProcess' cmd opts = do
-  (rv,output,err) <- liftIO $ readProcessWithExitCode cmd opts ""
+  (rv,output,err) <- liftIO (readProcessWithExitCode cmd opts "")
+      `modifyError'` GMEProcess ([cmd] ++ opts)
   case rv of
     ExitFailure val -> do
-        throwError $ strMsg $
+        throwError $ GMEProcess ([cmd] ++ opts) $ strMsg $
           cmd ++ " " ++ unwords opts ++ " (exit " ++ show val ++ ")"
               ++ "\n" ++ err
     ExitSuccess ->
         return output
 
-withDirectory_ :: FilePath -> IO a -> IO a
+withDirectory_ :: (MonadIO m, ExceptionMonad m) => FilePath -> m a -> m a
 withDirectory_ dir action =
-    bracket getCurrentDirectory setCurrentDirectory
-                (\_ -> setCurrentDirectory dir >> action)
-
-rethrowError :: MonadError e m => (e -> e) -> m a -> m a
-rethrowError f action = action `catchError` \e -> throwError $ f e
-
-tryFix :: MonadError e m => m a -> (e -> m ()) -> m a
-tryFix action fix = do
-  action `catchError` \e -> fix e >> action
-
--- | 'IOException's thrown in the computation passed to this function will be
--- converted to 'MonadError' failures using 'throwError'.
-liftIOExceptions :: (MonadIO m, Error e, MonadError e m) => IO a -> m a
-liftIOExceptions action = do
-  res <- liftIO $ tryIOError action
-  case res of
-    Right a -> return a
-    Left e -> case show e of
-                ""  -> throwError $ noMsg
-                msg -> throwError $ strMsg msg
+    gbracket (liftIO getCurrentDirectory) (liftIO . setCurrentDirectory)
+                (\_ -> liftIO (setCurrentDirectory dir) >> action)