added -z

Added -z option to git-annex commands that use --batch, useful for
supporting filenames containing newlines.

It only controls input to --batch, the output will still be line delimited
unless --json or etc is used to get some other output. While git often
makes -z affect both input and output, I don't like trying them together,
and making it affect output would have been a significant complication,
and also git-annex output is generally not intended to be machine parsed,
unless using --json or a format option.

Commands that take pairs like "file key" still separate them with a space
in --batch mode. All such commands take care to support filenames with
spaces when parsing that, so there was no need to change it, and it would
have needed significant changes to the batch machinery to separate tose
with a null.

To make fromkey and registerurl support -z, I had to give them a --batch
option. The implicit batch mode they enter when not provided with input
parameters does not support -z as that would have complicated option
parsing. Seemed better to move these toward using the same --batch as
everything else, though the implicit batch mode can still be used.

This commit was sponsored by Ole-Morten Duesund on Patreon.

CmdLine/Batch.hs

@@ -15,13 +15,24 @@ import Options.Applicative
 import Limit
 import Types.FileMatcher
 
-data BatchMode = Batch | NoBatch
+data BatchMode = Batch BatchFormat | NoBatch
+
+data BatchFormat = BatchLine | BatchNull
 
 parseBatchOption :: Parser BatchMode
-parseBatchOption = flag NoBatch Batch
-	( long "batch"
-	<> help "enable batch mode"
-	)
+parseBatchOption = go 
+	<$> switch
+		( long "batch"
+		<> help "enable batch mode"
+		)
+	<*> switch
+		( short 'z'
+		<> help "null delimited batch input"
+		)
+  where
+	go True False = Batch BatchLine
+ 	go True True = Batch BatchNull
+	go False _ = NoBatch
 
 -- A batchable command can run in batch mode, or not.
 -- In batch mode, one line at a time is read, parsed, and a reply output to
@@ -35,8 +46,10 @@ batchable handler parser paramdesc = batchseeker <$> batchparser
 		<*> parseBatchOption
 		<*> cmdParams paramdesc
 	
-	batchseeker (opts, NoBatch, params) = mapM_ (go NoBatch opts) params
-	batchseeker (opts, Batch, _) = batchInput Right (go Batch opts)
+	batchseeker (opts, NoBatch, params) =
+		mapM_ (go NoBatch opts) params
+	batchseeker (opts, batchmode@(Batch fmt), _) = 
+		batchInput fmt Right (go batchmode opts)
 
 	go batchmode opts p =
 		unlessM (handler opts p) $
@@ -46,11 +59,11 @@ batchable handler parser paramdesc = batchseeker <$> batchparser
 -- mode, exit on bad input.
 batchBadInput :: BatchMode -> Annex ()
 batchBadInput NoBatch = liftIO exitFailure
-batchBadInput Batch = liftIO $ putStrLn ""
+batchBadInput (Batch _) = liftIO $ putStrLn ""
 
 -- Reads lines of batch mode input and passes to the action to handle.
-batchInput :: (String -> Either String a) -> (a -> Annex ()) -> Annex ()
-batchInput parser a = go =<< batchLines
+batchInput :: BatchFormat -> (String -> Either String a) -> (a -> Annex ()) -> Annex ()
+batchInput fmt parser a = go =<< batchLines fmt
   where
 	go [] = return ()
 	go (l:rest) = do
@@ -58,8 +71,12 @@ batchInput parser a = go =<< batchLines
 		go rest
 	parseerr s = giveup $ "Batch input parse failure: " ++ s
 
-batchLines :: Annex [String]
-batchLines = liftIO $ lines <$> getContents
+batchLines :: BatchFormat -> Annex [String]
+batchLines fmt = liftIO $ splitter <$> getContents
+  where
+	splitter = case fmt of
+		BatchLine -> lines
+		BatchNull -> splitc '\0'
 
 -- Runs a CommandStart in batch mode.
 --
@@ -69,22 +86,22 @@ batchLines = liftIO $ lines <$> getContents
 -- any output, so in that case, batchBadInput is used to provide the caller
 -- with an empty line.
 batchCommandAction :: CommandStart -> Annex ()
-batchCommandAction a = maybe (batchBadInput Batch) (const noop)
+batchCommandAction a = maybe (batchBadInput (Batch BatchLine)) (const noop)
 	=<< callCommandAction' a
 
 -- Reads lines of batch input and passes the filepaths to a CommandStart
 -- to handle them.
 --
 -- File matching options are not checked.
-allBatchFiles :: (FilePath -> CommandStart) -> Annex ()
-allBatchFiles a = batchInput Right $ batchCommandAction . a
+allBatchFiles :: BatchFormat -> (FilePath -> CommandStart) -> Annex ()
+allBatchFiles fmt a = batchInput fmt Right $ batchCommandAction . a
 
 -- Like allBatchFiles, but checks the file matching options
 -- and skips non-matching files.
-batchFilesMatching :: (FilePath -> CommandStart) -> Annex ()
-batchFilesMatching a = do
+batchFilesMatching :: BatchFormat -> (FilePath -> CommandStart) -> Annex ()
+batchFilesMatching fmt a = do
 	matcher <- getMatcher
-	allBatchFiles $ \f ->
+	allBatchFiles fmt $ \f ->
 		ifM (matcher $ MatchingFile $ FileInfo f f)
 			( a f
 			, return Nothing