RawFilePath conversion of System.Directory

By using System.Directory.OsPath, which takes and returns OsString,
which is a ShortByteString. So, things like dirContents currently have the
overhead of copying that to a ByteString, but that should be less than
the overhead of using Strings which often in turn were converted to
RawFilePaths.

Added Utility.OsString and the OsString build flag. That flag is turned
on in the stack.yaml, and will be turned on automatically by cabal when
built with new enough libraries. The stack.yaml change is a bit ugly,
and that could be reverted for now if it causes any problems.

Note that Utility.OsString.toOsString on windows is avoiding only a
check of encoding that is documented as being unlikely to fail. I don't
think it can fail in git-annex; if it could, git-annex didn't contain
such an encoding check before, so at worst that should be a wash.

Annex/Ssh.hs

@@ -5,6 +5,7 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE CPP #-}
 
 module Annex.Ssh (
@@ -100,15 +101,16 @@ consumeStdinParams NoConsumeStdin = [Param "-n"]
 
 {- Returns a filename to use for a ssh connection caching socket, and
  - parameters to enable ssh connection caching. -}
-sshCachingInfo :: (SshHost, Maybe Integer) -> Annex (Maybe FilePath, [CommandParam])
+sshCachingInfo :: (SshHost, Maybe Integer) -> Annex (Maybe RawFilePath, [CommandParam])
 sshCachingInfo (host, port) = go =<< sshCacheDir'
   where
 	go (Right dir) =
 		liftIO (bestSocketPath $ dir P.</> hostport2socket host port) >>= return . \case
 			Nothing -> (Nothing, [])
 			Just socketfile -> 
-				let socketfile' = fromRawFilePath socketfile
-				in (Just socketfile', sshConnectionCachingParams socketfile')
+				(Just socketfile
+				, sshConnectionCachingParams (fromRawFilePath socketfile)
+				)
 	-- No connection caching with concurrency is not a good
 	-- combination, so warn the user.
 	go (Left whynocaching) = do
@@ -214,7 +216,7 @@ portParams (Just port) = [Param "-p", Param $ show port]
  - Locks the socket lock file to prevent other git-annex processes from
  - stopping the ssh multiplexer on this socket.
  -}
-prepSocket :: FilePath -> SshHost -> [CommandParam] -> Annex ()
+prepSocket :: RawFilePath -> SshHost -> [CommandParam] -> Annex ()
 prepSocket socketfile sshhost sshparams = do
 	-- There could be stale ssh connections hanging around
 	-- from a previous git-annex run that was interrupted.
@@ -286,13 +288,13 @@ prepSocket socketfile sshhost sshparams = do
  - and this check makes such files be skipped since the corresponding lock
  - file won't exist.
  -}
-enumSocketFiles :: Annex [FilePath]
+enumSocketFiles :: Annex [RawFilePath]
 enumSocketFiles = liftIO . go =<< sshCacheDir
   where
 	go Nothing = return []
 	go (Just dir) = filterM (R.doesPathExist . socket2lock)
 		=<< filter (not . isLock)
-		<$> catchDefaultIO [] (dirContents (fromRawFilePath dir))
+		<$> catchDefaultIO [] (dirContents dir)
 
 {- Stop any unused ssh connection caching processes. -}
 sshCleanup :: Annex ()
@@ -324,9 +326,9 @@ sshCleanup = mapM_ cleanup =<< enumSocketFiles
 forceSshCleanup :: Annex ()
 forceSshCleanup = mapM_ forceStopSsh =<< enumSocketFiles
 
-forceStopSsh :: FilePath -> Annex ()
+forceStopSsh :: RawFilePath -> Annex ()
 forceStopSsh socketfile = withNullHandle $ \nullh -> do
-	let (dir, base) = splitFileName socketfile
+	let (dir, base) = splitFileName (fromRawFilePath socketfile)
 	let p = (proc "ssh" $ toCommand $
 		[ Param "-O", Param "stop" ] ++ 
 		sshConnectionCachingParams base ++ 
@@ -338,7 +340,7 @@ forceStopSsh socketfile = withNullHandle $ \nullh -> do
 		}
 	void $ liftIO $ catchMaybeIO $ withCreateProcess p $ \_ _ _ pid ->
 		forceSuccessProcess p pid
-	liftIO $ removeWhenExistsWith R.removeLink (toRawFilePath socketfile)
+	liftIO $ removeWhenExistsWith R.removeLink socketfile
 
 {- This needs to be as short as possible, due to limitations on the length
  - of the path to a socket file. At the same time, it needs to be unique
@@ -355,13 +357,13 @@ hostport2socket' s
   where
 	lengthofmd5s = 32
 
-socket2lock :: FilePath -> RawFilePath
-socket2lock socket = toRawFilePath (socket ++ lockExt)
+socket2lock :: RawFilePath -> RawFilePath
+socket2lock socket = socket <> lockExt
 
-isLock :: FilePath -> Bool
-isLock f = lockExt `isSuffixOf` f
+isLock :: RawFilePath -> Bool
+isLock f = lockExt `S.isSuffixOf` f
 
-lockExt :: String
+lockExt :: S.ByteString
 lockExt = ".lock"
 
 {- This is the size of the sun_path component of sockaddr_un, which