Factor out readProcess'

Language/Haskell/GhcMod/Utils.hs

@@ -1,5 +1,20 @@
 module Language.Haskell.GhcMod.Utils where
 
+import Control.Exception (bracket)
+import System.Directory (getCurrentDirectory, setCurrentDirectory)
+import System.Process (readProcessWithExitCode)
+import System.Exit (ExitCode(..))
+import System.IO (hPutStrLn, stderr)
+
 -- dropWhileEnd is not provided prior to base 4.5.0.0.
 dropWhileEnd :: (a -> Bool) -> [a] -> [a]
 dropWhileEnd p = foldr (\x xs -> if p x && null xs then [] else x : xs) []
+readProcess' :: String -> [String] -> IO String
+readProcess' cmd opts = do
+  (rv,output,err) <- readProcessWithExitCode cmd opts ""
+  case rv of
+    ExitFailure val -> do
+        hPutStrLn stderr err
+        fail $ cmd ++ " " ++ unwords opts ++ " (exit " ++ show val ++ ")"
+    ExitSuccess ->
+        return output