git annex add -u now supported, analagous to git add -u

Unlike git add -u, git annex add -u does not update the index for files
removed from the working tree. But then, "git add ." stages removals,
and "git annex add ." does not, so that's an existing divergence.

Seems that --update --batch would need to run git ls-files once per line of
batch input, which would surely be too slow, so just throw an error for
that.

This commit was supported by the NSF-funded DataLad project.

Command/Add.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010, 2013 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2017 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -30,6 +30,7 @@ data AddOptions = AddOptions
 	{ addThese :: CmdParams
 	, includeDotFiles :: Bool
 	, batchOption :: BatchMode
+	, updateOnly :: Bool
 	}
 
 optParser :: CmdParamsDesc -> Parser AddOptions
@@ -40,6 +41,11 @@ optParser desc = AddOptions
 		<> help "don't skip dotfiles"
 		)
 	<*> parseBatchOption
+	<*> switch
+		( long "update"
+		<> short 'u'
+		<> help "only update tracked files"
+		)
 
 seek :: AddOptions -> CommandSeek
 seek o = allowConcurrentOutput $ do
@@ -52,10 +58,14 @@ seek o = allowConcurrentOutput $ do
 			)
 		)
 	case batchOption o of
-		Batch -> batchFiles gofile
+		Batch
+			| updateOnly o ->
+				giveup "--update --batch is not supported"
+			| otherwise -> batchFiles gofile
 		NoBatch -> do
 			let go a = a gofile (addThese o)
-			go (withFilesNotInGit (not $ includeDotFiles o))
+			unless (updateOnly o) $
+				go (withFilesNotInGit (not $ includeDotFiles o))
 			go withFilesMaybeModified
 			unlessM (versionSupportsUnlockedPointers <||> isDirect) $
 				go withFilesOldUnlocked