GHC 8 readiness

Language/Haskell/GhcMod/Logger.hs

@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 module Language.Haskell.GhcMod.Logger (
     withLogger
   , withLogger'
@@ -135,12 +137,21 @@ ppErrMsg err = do
     dflags <- asks gpeDynFlags
     let unqual = errMsgContext err
         st = Gap.mkErrStyle' dflags unqual
+#if __GLASGOW_HASKELL__ < 800
     let ext = showPage dflags st (errMsgExtraInfo err)
+#endif
     m <- ppMsg st spn SevError msg
-    return $ m ++ (if null ext then "" else "\n" ++ ext)
+    return $ m
+#if __GLASGOW_HASKELL__ < 800
+        ++ (if null ext then "" else "\n" ++ ext)
+#endif
    where
      spn = Gap.errorMsgSpan err
+#if __GLASGOW_HASKELL__ >= 800
+     msg = pprLocErrMsg err
+#else
      msg = errMsgShortDoc err
+#endif
 
 ppMsg :: PprStyle -> SrcSpan -> Severity -> SDoc -> GmPprEnvM String
 ppMsg st spn sev msg = do