Format ExitCodeException stdout and stderr with UTF-8

Closes #86

Author: tomjaguarpaw

package.yaml

@@ -19,6 +19,7 @@ dependencies:
 - bytestring
 - process >=1.2
 - stm
+- text
 - transformers
 - unliftio-core
 

src/System/Process/Typed/Internal.hs

@@ -26,6 +26,9 @@ import qualified Data.ByteString.Lazy as L
 import qualified Data.ByteString.Lazy.Char8 as L8
 import Data.String (IsString (fromString))
 import Control.Monad.IO.Unlift
+import qualified Data.Text.Encoding.Error as TEE
+import qualified Data.Text.Lazy as TL
+import qualified Data.Text.Lazy.Encoding as TLE
 
 #if MIN_VERSION_process(1, 4, 0) && !WINDOWS
 import System.Posix.Types (GroupID, UserID)
@@ -620,11 +623,13 @@ instance Show ExitCodeException where
         , show (eceProcessConfig ece) { pcEnv = Nothing }
         , if L.null (eceStdout ece)
             then ""
-            else "Standard output:\n\n" ++ L8.unpack (eceStdout ece)
+            else "Standard output:\n\n" ++ unpack (eceStdout ece)
         , if L.null (eceStderr ece)
             then ""
-            else "Standard error:\n\n" ++ L8.unpack (eceStderr ece)
+            else "Standard error:\n\n" ++ unpack (eceStderr ece)
         ]
+      where
+        unpack = TL.unpack . TLE.decodeUtf8With TEE.lenientDecode
 
 -- | Wrapper for when an exception is thrown when reading from a child
 -- process, used by 'byteStringOutput'.