fix mojibake reversion in display of utf8

When displaying a ByteString like "💕", safeOutput operates on
individual bytes like "\240\159\146\149" and isControl '\146' = True,
so it got truncated to just "\240".

So, only treat the low control characters, and DEL, as control
characters.

Also split Utility.Terminal out of Utility.SafeOutput. The latter needs
win32, but Utility.SafeOutput is used by Control.Exception, which is
used by Setup.

Sponsored-by: Nicholas Golder-Manning on Patreon

Utility/SafeOutput.hs

@@ -11,55 +11,27 @@
 
 module Utility.SafeOutput (
 	safeOutput,
-	IsTerminal(..),
-	checkIsTerminal,
+	safeOutputChar,
 ) where
 
 import Data.Char
 import qualified Data.ByteString as S
 import System.IO
-#ifdef mingw32_HOST_OS
-import System.Win32.MinTTY (isMinTTYHandle)
-import System.Win32.File
-import System.Win32.Types
-import Graphics.Win32.Misc
-import Control.Exception
-#endif
 
 class SafeOutputtable t where
 	safeOutput :: t -> t
 
 instance SafeOutputtable String where
-	safeOutput = filter safeChar
+	safeOutput = filter safeOutputChar
 
 instance SafeOutputtable S.ByteString where
-	safeOutput = S.filter (safeChar . chr . fromIntegral)
+	safeOutput = S.filter (safeOutputChar . chr . fromIntegral)
 
-safeChar :: Char -> Bool
-safeChar c
+safeOutputChar :: Char -> Bool
+safeOutputChar c
 	| not (isControl c) = True
 	| c == '\n' = True
 	| c == '\t' = True
+	| c == '\DEL' = False
+	| ord c > 31 = True
 	| otherwise = False
-
-newtype IsTerminal = IsTerminal Bool
-
-checkIsTerminal :: Handle -> IO IsTerminal
-checkIsTerminal h = do
-#ifndef mingw32_HOST_OS
-	b <- hIsTerminalDevice h
-	return (IsTerminal b)
-#else
-	b <- hIsTerminalDevice h
-	if b
-		then return (IsTerminal b)
-		else do
-			h' <- getStdHandle sTD_OUTPUT_HANDLE
-				`catch` \(_ :: IOError) ->
-					return nullHANDLE
-			if h == nullHANDLE
-				then return (IsTerminal False)
-				else do
-					b' <- isMinTTYHandle h'
-					return (IsTerminal b)
-#endif