Reinstate cwd setup, this time with locking

test/MonadSpec.hs

@@ -3,6 +3,8 @@ module MonadSpec where
 import Test.Hspec
 import TestUtils
 import Control.Monad.Error.Class
+import Control.Concurrent
+import Control.Exception
 
 spec :: Spec
 spec = do
@@ -15,3 +17,21 @@ spec = do
                          return "hello"
                      `catchError` (const $ fail "oh noes")
              a `shouldBe` (Left $ GMEString "oh noes")
+
+    describe "runGhcModT" $
+        it "throws an exception when run in multiple threads" $ do
+          mv1 :: MVar (Either SomeException ())
+              <- newEmptyMVar
+          mv2 :: MVar (Either SomeException ())
+              <- newEmptyMVar
+
+          _ <- forkOS $ putMVar mv1 =<< (try $ evaluate =<< (runD $ liftIO $ readMVar mv2 >> return ()))
+          _ <- forkOS $ putMVar mv2 =<< (try $ evaluate =<< (runD $ return ()))
+          e1 <- takeMVar mv1
+          e2 <- takeMVar mv2
+
+          (isLeft e1 || isLeft e2) `shouldBe` True
+
+isLeft :: Either a b -> Bool
+isLeft (Right _) = False
+isLeft (Left _) = True

test/TestUtils.hs

@@ -45,20 +45,7 @@ extract action = do
 
 withSpecCradle :: (IOish m, GmOut m) => FilePath -> ((Cradle, GhcModLog) -> m a) -> m a
 withSpecCradle cradledir f = do
-    gbracket (runJournalT $ findSpecCradle cradledir) (liftIO . cleanupCradle . fst) $ \arg@(crdl,_) ->
-      bracketWorkingDirectory (cradleRootDir crdl) $
-        f arg
-
-bracketWorkingDirectory ::
-    (ExceptionMonad m, MonadIO m) => FilePath -> m c -> m c
-bracketWorkingDirectory dir a =
-    gbracket (swapWorkingDirectory dir) (liftIO . setCurrentDirectory) (const a)
-
-swapWorkingDirectory :: MonadIO m => FilePath -> m FilePath
-swapWorkingDirectory ndir = liftIO $ do
-  odir <- getCurrentDirectory >>= canonicalizePath
-  setCurrentDirectory $ ndir
-  return odir
+    gbracket (runJournalT $ findSpecCradle cradledir) (liftIO . cleanupCradle . fst) f
 
 runGhcModTSpec :: Options -> GhcModT IO a -> IO (Either GhcModError a, GhcModLog)
 runGhcModTSpec opt action = do