convert encode_c to ByteString

This turns out to be possible after all, because the old one decomposed
a unicode Char to multiple Word8s and encoded those. It should be faster
in some places, particularly in Git.Filename.encodeAlways.

The old version encoded all unicode by default as well as ascii control
characters and also '"'. The new one only encodes ascii control
characters by default.

That old behavior was visible in Utility.Format.format, which did escape
'"' when used in eg git-annex find --format='${escaped_file}\n'
So made sure to keep that working the same. Although the man page only
says it will escape "unusual" characters, so it might be able to be
changed.

Git.Filename.encodeAlways also needs to escape '"' ; that was the
original reason that was escaped.

Types.Transferrer I judge is ok to not escape '"', because the escaped
value is sent in a line-based protocol, which is decoded at the other
end by decode_c. So old git-annex and new will be fine whether that is
escaped or not, the result will be the same.

Note that when asked to escape a double quote, it is escaped to \"
rather than to \042. That's the same behavior as git has. It's
perhaps somehow more of a special case than it needs to be.

Sponsored-by: k0ld on Patreon

Git/Filename.hs

@@ -1,15 +1,17 @@
 {- Some git commands output encoded filenames, in a rather annoyingly complex
  - C-style encoding.
  -
- - Copyright 2010, 2011 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2023 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Git.Filename where
 
 import Common
-import Utility.Format (decode_c, encode_c)
+import Utility.Format (decode_c, encode_c, isUtf8Byte)
 import Utility.QuickCheck
 
 import Data.Char
@@ -31,9 +33,11 @@ decode b = case S.uncons b of
   	q :: Word8
 	q = fromIntegral (ord '"')
 
-{- Should not need to use this, except for testing decode. -}
-encode :: RawFilePath -> S.ByteString
-encode s = encodeBS $ "\"" ++ encode_c (decodeBS s) ++ "\""
+-- always encodes and double quotes, even in cases that git does not
+encodeAlways :: RawFilePath -> S.ByteString
+encodeAlways s = "\"" <> encode_c needencode s <> "\""
+  where
+	needencode c = isUtf8Byte c || c == fromIntegral (ord '"')
 
 -- Encoding and then decoding roundtrips only when the string does not
 -- contain high unicode, because eg,  both "\12345" and "\227\128\185"
@@ -43,6 +47,6 @@ encode s = encodeBS $ "\"" ++ encode_c (decodeBS s) ++ "\""
 -- limits what's tested to ascii, so avoids running into it.
 prop_encode_decode_roundtrip :: TestableFilePath -> Bool
 prop_encode_decode_roundtrip ts = 
-	s == fromRawFilePath (decode (encode (toRawFilePath s)))
+	s == fromRawFilePath (decode (encodeAlways (toRawFilePath s)))
   where
 	s = fromTestableFilePath ts