Always use filesystem encoding for all file and handle reads and writes.

This is a big scary change. I have convinced myself it should be safe. I
hope!

Utility/FileSystemEncoding.hs

@@ -1,6 +1,6 @@
 {- GHC File system encoding handling.
  -
- - Copyright 2012-2014 Joey Hess <id@joeyh.name>
+ - Copyright 2012-2016 Joey Hess <id@joeyh.name>
  -
  - License: BSD-2-clause
  -}
@@ -9,7 +9,7 @@
 {-# OPTIONS_GHC -fno-warn-tabs #-}
 
 module Utility.FileSystemEncoding (
-	fileEncoding,
+	useFileSystemEncoding,
 	withFilePath,
 	md5FilePath,
 	decodeBS,
@@ -19,7 +19,6 @@ module Utility.FileSystemEncoding (
 	encodeW8NUL,
 	decodeW8NUL,
 	truncateFilePath,
-	setConsoleEncoding,
 ) where
 
 import qualified GHC.Foreign as GHC
@@ -39,19 +38,30 @@ import qualified Data.ByteString.Lazy.UTF8 as L8
 
 import Utility.Exception
 
-{- Sets a Handle to use the filesystem encoding. This causes data
- - written or read from it to be encoded/decoded the same
- - as ghc 7.4 does to filenames etc. This special encoding
- - allows "arbitrary undecodable bytes to be round-tripped through it".
+{- Makes all subsequent Handles that are opened, as well as stdio Handles,
+ - use the filesystem encoding, instead of the encoding of the current
+ - locale.
+ -
+ - The filesystem encoding allows "arbitrary undecodable bytes to be
+ - round-tripped through it". This avoids encoded failures when data is not
+ - encoded matching the current locale.
+ -
+ - Note that code can still use hSetEncoding to change the encoding of a
+ - Handle. This only affects the default encoding.
  -}
-fileEncoding :: Handle -> IO ()
+useFileSystemEncoding :: IO ()
+useFileSystemEncoding = do
 #ifndef mingw32_HOST_OS
-fileEncoding h = hSetEncoding h =<< Encoding.getFileSystemEncoding
+	e <- Encoding.getFileSystemEncoding
 #else
-{- The file system encoding does not work well on Windows,
- - and Windows only has utf FilePaths anyway. -}
-fileEncoding h = hSetEncoding h Encoding.utf8
+	{- The file system encoding does not work well on Windows,
+	 - and Windows only has utf FilePaths anyway. -}
+	let e = Encoding.utf8
 #endif
+	hSetEncoding stdin e
+	hSetEncoding stdout e
+	hSetEncoding stderr e
+	Encoding.setLocaleEncoding e	
 
 {- Marshal a Haskell FilePath into a NUL terminated C string using temporary
  - storage. The FilePath is encoded using the filesystem encoding,
@@ -165,10 +175,3 @@ truncateFilePath n = reverse . go [] n . L8.fromString
 					else go (c:coll) (cnt - x') (L8.drop 1 bs)
 			_ -> coll
 #endif
-
-{- This avoids ghc's output layer crashing on invalid encoded characters in
- - filenames when printing them out. -}
-setConsoleEncoding :: IO ()
-setConsoleEncoding = do
-	fileEncoding stdout
-	fileEncoding stderr