Give readProcess' more sensible error messages.

Also a bunch of refactoring for GhcModError

test/FindSpec.hs

@@ -2,10 +2,11 @@ module FindSpec where
 
 import Language.Haskell.GhcMod.Find
 import Test.Hspec
+import TestUtils
 
 spec :: Spec
 spec = do
     describe "db <- loadSymbolDb" $ do
         it "lookupSymbol' db \"head\"  contains at least `Data.List'" $ do
-            db <- loadSymbolDb
+            db <- runD loadSymbolDb
             lookupSym "head" db `shouldContain` ["Data.List"]

test/MonadSpec.hs

@@ -5,6 +5,7 @@ import Test.Hspec
 import Dir
 import TestUtils
 import Control.Applicative
+import Control.Exception
 import Control.Monad.Error.Class
 
 spec :: Spec
@@ -27,3 +28,12 @@ spec = do
         it "work" $ do
           (runD $ gmsPut (GhcModState Intelligent) >> gmsGet)
             `shouldReturn` (GhcModState Intelligent)
+
+    describe "liftIO" $ do
+        it "converts user errors to GhcModError" $ do
+            shouldReturnError $
+                runD' $ liftIO $ throw (userError "hello") >> return ""
+
+        it "converts a file not found exception to GhcModError" $ do
+            shouldReturnError $
+                runD' $ liftIO $ readFile "/DOES_NOT_EXIST" >> return ""

test/UtilsSpec.hs

@@ -1,7 +1,7 @@
 module UtilsSpec where
 
+import Language.Haskell.GhcMod.Error
 import Language.Haskell.GhcMod.Utils
-import Control.Exception
 import TestUtils
 import Test.Hspec
 
@@ -15,7 +15,9 @@ spec = do
     describe "liftMonadError" $ do
         it "converts IOErrors to GhcModError" $ do
             shouldReturnError $
-                runD' $ liftIOExceptions $ throw (userError "hello") >> return ""
+                runD' $ liftIO $ throw (userError "hello") >> return ""
 
             shouldReturnError $
-                runD' $ liftIOExceptions $ readFile "/DOES_NOT_EXIST" >> return ""
+                runD' $ liftIO $ readFile "/DOES_NOT_EXIST" >> return ""
+
+-- readProcessWithExitCode cmd opts ""