rework git check-attr interface

Now gitattributes are looked up, efficiently, in only the places that
really need them, using the same approach used for cat-file.

The old CheckAttr code seemed very fragile, in the way it streamed files
through git check-attr.
I actually found that cad8824852aa0623dc41eac02a9e2bae47d88ec4
was still deadlocking with ghc 7.4, at the end of adding a lot of files.
This should fix that problem, and avoid future ones.

The best part is that this removes withAttrFilesInGit and withNumCopies,
which were complicated Seek methods, as well as simplfying the types
for several other Seek methods that had a Backend tupled in.

16 files changed, 141 insertions, 97 deletions

diff --git a/Annex.hs b/Annex.hs
index de36c816d..534415207 100644
--- a/Annex.hs
+++ b/Annex.hs
@@ -35,6 +35,7 @@ import Common
 import qualified Git
 import qualified Git.Config
 import Git.CatFile
+import Git.CheckAttr
 import qualified Git.Queue
 import Types.Backend
 import qualified Types.Remote
@@ -82,6 +83,7 @@ data AnnexState = AnnexState
 	, auto :: Bool
 	, branchstate :: BranchState
 	, catfilehandle :: Maybe CatFileHandle
+	, checkattrhandle :: Maybe CheckAttrHandle
 	, forcebackend :: Maybe String
 	, forcenumcopies :: Maybe Int
 	, limit :: Matcher (FilePath -> Annex Bool)
@@ -105,6 +107,7 @@ newState gitrepo = AnnexState
 	, auto = False
 	, branchstate = startBranchState
 	, catfilehandle = Nothing
+	, checkattrhandle = Nothing
 	, forcebackend = Nothing
 	, forcenumcopies = Nothing
 	, limit = Left []
diff --git a/Annex/CheckAttr.hs b/Annex/CheckAttr.hs
new file mode 100644
index 000000000..01779e813
--- /dev/null
+++ b/Annex/CheckAttr.hs
@@ -0,0 +1,35 @@
+{- git check-attr interface, with handle automatically stored in the Annex monad
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.CheckAttr (
+	checkAttr,
+	checkAttrHandle
+) where
+
+import Common.Annex
+import qualified Git.CheckAttr as Git
+import qualified Annex
+
+{- All gitattributes used by git-annex. -}
+annexAttrs :: [Git.Attr]
+annexAttrs =
+	[ "annex.backend"
+	, "annex.numcopies"
+	]
+
+checkAttr :: Git.Attr -> FilePath -> Annex String
+checkAttr attr file = do
+	h <- checkAttrHandle
+	liftIO $ Git.checkAttr h attr file
+
+checkAttrHandle :: Annex Git.CheckAttrHandle
+checkAttrHandle = maybe startup return =<< Annex.getState Annex.checkattrhandle
+	where
+		startup = do
+			h <- inRepo $ Git.checkAttrStart annexAttrs
+			Annex.changeState $ \s -> s { Annex.checkattrhandle = Just h }
+			return h
diff --git a/Backend.hs b/Backend.hs
index e351bb3b2..50c89ecc5 100644
--- a/Backend.hs
+++ b/Backend.hs
@@ -6,12 +6,11 @@
  -}
 
 module Backend (
-	BackendFile,
 	list,
 	orderedList,
 	genKey,
 	lookupFile,
-	chooseBackends,
+	chooseBackend,
 	lookupBackendName,
 	maybeLookupBackendName
 ) where
@@ -22,6 +21,7 @@ import Common.Annex
 import qualified Git.Config
 import qualified Git.CheckAttr
 import qualified Annex
+import Annex.CheckAttr
 import Types.Key
 import qualified Types.Backend as B
 
@@ -93,20 +93,15 @@ lookupFile file = do
 						bname ++ ")"
 					return Nothing
 
-type BackendFile = (Maybe Backend, FilePath)
-
-{- Looks up the backends that should be used for each file in a list.
+{- Looks up the backend that should be used for a file.
  - That can be configured on a per-file basis in the gitattributes file.
  -}
-chooseBackends :: [FilePath] -> Annex [BackendFile]
-chooseBackends fs = Annex.getState Annex.forcebackend >>= go
+chooseBackend :: FilePath -> Annex (Maybe Backend)
+chooseBackend f = Annex.getState Annex.forcebackend >>= go
 	where
-		go Nothing = do
-			pairs <- inRepo $ Git.CheckAttr.lookup "annex.backend" fs
-			return $ map (\(f,b) -> (maybeLookupBackendName b, f)) pairs
-		go (Just _) = do
-			l <- orderedList
-			return $ map (\f -> (Just $ Prelude.head l, f)) fs
+		go Nothing =  maybeLookupBackendName <$>
+			checkAttr "annex.backend" f
+		go (Just _) = Just . Prelude.head <$> orderedList
 
 {- Looks up a backend by name. May fail if unknown. -}
 lookupBackendName :: String -> Backend
diff --git a/Command.hs b/Command.hs
index 386efafde..e7ce335c7 100644
--- a/Command.hs
+++ b/Command.hs
@@ -18,6 +18,7 @@ module Command (
 	ifAnnexed,
 	notBareRepo,
 	isBareRepo,
+	numCopies,
 	autoCopies,
 	module ReExported
 ) where
@@ -34,6 +35,7 @@ import Checks as ReExported
 import Usage as ReExported
 import Logs.Trust
 import Config
+import Annex.CheckAttr
 
 {- Generates a normal command -}
 command :: String -> String -> [CommandSeek] -> String -> Command
@@ -98,17 +100,22 @@ notBareRepo a = do
 isBareRepo :: Annex Bool
 isBareRepo = fromRepo Git.repoIsLocalBare
 
+numCopies :: FilePath  -> Annex (Maybe Int)
+numCopies file = readish <$> checkAttr "annex.numcopies" file
+
 {- Used for commands that have an auto mode that checks the number of known
  - copies of a key.
  -
  - In auto mode, first checks that the number of known
  - copies of the key is > or < than the numcopies setting, before running
  - the action. -}
-autoCopies :: Key -> (Int -> Int -> Bool) -> Maybe Int -> CommandStart -> CommandStart
-autoCopies key vs numcopiesattr a = Annex.getState Annex.auto >>= auto
+autoCopies :: FilePath -> Key -> (Int -> Int -> Bool) -> (Maybe Int -> CommandStart) -> CommandStart
+autoCopies file key vs a = do
+	numcopiesattr <- numCopies file
+	Annex.getState Annex.auto >>= auto numcopiesattr
 	where
-		auto False = a
-		auto True = do
+		auto numcopiesattr False = a numcopiesattr
+		auto numcopiesattr True = do
 			needed <- getNumCopies numcopiesattr
 			(_, have) <- trustPartition UnTrusted =<< Remote.keyLocations key
-			if length have `vs` needed then a else stop
+			if length have `vs` needed then a numcopiesattr else stop
diff --git a/Command/Add.hs b/Command/Add.hs
index 9410601b8..28971529a 100644
--- a/Command/Add.hs
+++ b/Command/Add.hs
@@ -16,7 +16,6 @@ import qualified Backend
 import Logs.Location
 import Annex.Content
 import Utility.Touch
-import Backend
 
 def :: [Command]
 def = [command "add" paramPaths seek "add files to annex"]
@@ -28,8 +27,8 @@ seek = [withFilesNotInGit start, withFilesUnlocked start]
 {- The add subcommand annexes a file, storing it in a backend, and then
  - moving it into the annex directory and setting up the symlink pointing
  - to its content. -}
-start :: BackendFile -> CommandStart
-start p@(_, file) = notBareRepo $ ifAnnexed file fixup add
+start :: FilePath -> CommandStart
+start file = notBareRepo $ ifAnnexed file fixup add
 	where
 		add = do
 			s <- liftIO $ getSymbolicLinkStatus file
@@ -37,7 +36,7 @@ start p@(_, file) = notBareRepo $ ifAnnexed file fixup add
 				then stop
 				else do
 					showStart "add" file
-					next $ perform p
+					next $ perform file
 		fixup (key, _) = do
 			-- fixup from an interrupted add; the symlink
 			-- is present but not yet added to git
@@ -45,8 +44,10 @@ start p@(_, file) = notBareRepo $ ifAnnexed file fixup add
 			liftIO $ removeFile file
 			next $ next $ cleanup file key =<< inAnnex key
 
-perform :: BackendFile -> CommandPerform
-perform (backend, file) = Backend.genKey file backend >>= go
+perform :: FilePath -> CommandPerform
+perform file = do
+	backend <- Backend.chooseBackend file
+	Backend.genKey file backend >>= go
 	where
 		go Nothing = stop
 		go (Just (key, _)) = do
diff --git a/Command/AddUrl.hs b/Command/AddUrl.hs
index db73f14e9..f91d6dd55 100644
--- a/Command/AddUrl.hs
+++ b/Command/AddUrl.hs
@@ -63,7 +63,7 @@ download url file = do
 	tmp <- fromRepo $ gitAnnexTmpLocation dummykey
 	liftIO $ createDirectoryIfMissing True (parentDir tmp)
 	stopUnless (downloadUrl [url] tmp) $ do
-		[(backend, _)] <- Backend.chooseBackends [file]
+		backend <- Backend.chooseBackend file
 		k <- Backend.genKey tmp backend
 		case k of
 			Nothing -> stop
diff --git a/Command/Copy.hs b/Command/Copy.hs
index 32b83a526..a8ec22570 100644
--- a/Command/Copy.hs
+++ b/Command/Copy.hs
@@ -19,10 +19,10 @@ def = [withOptions Command.Move.options $ command "copy" paramPaths seek
 seek :: [CommandSeek]
 seek = [withField Command.Move.toOption Remote.byName $ \to ->
 		withField Command.Move.fromOption Remote.byName $ \from ->
-			withNumCopies $ \n -> whenAnnexed $ start to from n]
+			withFilesInGit $ whenAnnexed $ start to from]
 
 -- A copy is just a move that does not delete the source file.
 -- However, --auto mode avoids unnecessary copies.
-start :: Maybe Remote -> Maybe Remote -> Maybe Int -> FilePath -> (Key, Backend) -> CommandStart
-start to from numcopies file (key, backend) = autoCopies key (<) numcopies $
+start :: Maybe Remote -> Maybe Remote -> FilePath -> (Key, Backend) -> CommandStart
+start to from file (key, backend) = autoCopies file key (<) $ \_numcopies ->
 	Command.Move.start to from False file (key, backend)
diff --git a/Command/Drop.hs b/Command/Drop.hs
index b40de00cb..9eb36a22f 100644
--- a/Command/Drop.hs
+++ b/Command/Drop.hs
@@ -26,11 +26,11 @@ fromOption :: Option
 fromOption = Option.field ['f'] "from" paramRemote "drop content from a remote"
 
 seek :: [CommandSeek]
-seek = [withField fromOption Remote.byName $ \from -> withNumCopies $ \n ->
-	whenAnnexed $ start from n]
+seek = [withField fromOption Remote.byName $ \from ->
+	withFilesInGit $ whenAnnexed $ start from]
 
-start :: Maybe Remote -> Maybe Int -> FilePath -> (Key, Backend) -> CommandStart
-start from numcopies file (key, _) = autoCopies key (>) numcopies $ do
+start :: Maybe Remote -> FilePath -> (Key, Backend) -> CommandStart
+start from file (key, _) = autoCopies file key (>) $ \numcopies -> do
 	case from of
 		Nothing -> startLocal file numcopies key
 		Just remote -> do
diff --git a/Command/Fsck.hs b/Command/Fsck.hs
index 469fad749..94b360104 100644
--- a/Command/Fsck.hs
+++ b/Command/Fsck.hs
@@ -36,12 +36,13 @@ options = [fromOption]
 seek :: [CommandSeek]
 seek =
 	[ withField fromOption Remote.byName $ \from ->
-		withNumCopies $ \n -> whenAnnexed $ start from n
+		withFilesInGit $ whenAnnexed $ start from
 	, withBarePresentKeys startBare
 	]
 
-start :: Maybe Remote -> Maybe Int -> FilePath -> (Key, Backend) -> CommandStart
-start from numcopies file (key, backend) = do
+start :: Maybe Remote -> FilePath -> (Key, Backend) -> CommandStart
+start from file (key, backend) = do
+	numcopies <- numCopies file
 	showStart "fsck" file
 	case from of
 		Nothing -> next $ perform key file backend numcopies
diff --git a/Command/Get.hs b/Command/Get.hs
index 5d032e13c..928ab0f1b 100644
--- a/Command/Get.hs
+++ b/Command/Get.hs
@@ -19,11 +19,11 @@ def = [withOptions [Command.Move.fromOption] $ command "get" paramPaths seek
 
 seek :: [CommandSeek]
 seek = [withField Command.Move.fromOption Remote.byName $ \from ->
-	withNumCopies $ \n -> whenAnnexed $ start from n]
+	withFilesInGit $ whenAnnexed $ start from]
 
-start :: Maybe Remote -> Maybe Int -> FilePath -> (Key, Backend) -> CommandStart
-start from numcopies file (key, _) = stopUnless (not <$> inAnnex key) $
-	autoCopies key (<) numcopies $ do
+start :: Maybe Remote -> FilePath -> (Key, Backend) -> CommandStart
+start from file (key, _) = stopUnless (not <$> inAnnex key) $
+	autoCopies file key (<) $ \_numcopies -> do
 		case from of
 			Nothing -> go $ perform key
 			Just src -> do
diff --git a/Command/Lock.hs b/Command/Lock.hs
index 329fd3eff..b8aedb252 100644
--- a/Command/Lock.hs
+++ b/Command/Lock.hs
@@ -10,7 +10,6 @@ module Command.Lock where
 import Common.Annex
 import Command
 import qualified Annex.Queue
-import Backend
 	
 def :: [Command]
 def = [command "lock" paramPaths seek "undo unlock command"]
@@ -18,9 +17,8 @@ def = [command "lock" paramPaths seek "undo unlock command"]
 seek :: [CommandSeek]
 seek = [withFilesUnlocked start, withFilesUnlockedToBeCommitted start]
 
-{- Undo unlock -}
-start :: BackendFile -> CommandStart
-start (_, file) = do
+start :: FilePath -> CommandStart
+start file = do
 	showStart "lock" file
 	next $ perform file
 
diff --git a/Command/Migrate.hs b/Command/Migrate.hs
index f6467463d..c6b0f086c 100644
--- a/Command/Migrate.hs
+++ b/Command/Migrate.hs
@@ -19,12 +19,12 @@ def :: [Command]
 def = [command "migrate" paramPaths seek "switch data to different backend"]
 
 seek :: [CommandSeek]
-seek = [withBackendFilesInGit $ \(b, f) -> whenAnnexed (start b) f]
+seek = [withFilesInGit $ whenAnnexed start]
 
-start :: Maybe Backend -> FilePath -> (Key, Backend) -> CommandStart
-start b file (key, oldbackend) = do
+start :: FilePath -> (Key, Backend) -> CommandStart
+start file (key, oldbackend) = do
 	exists <- inAnnex key
-	newbackend <- choosebackend b
+	newbackend <- choosebackend =<< Backend.chooseBackend file
 	if (newbackend /= oldbackend || upgradableKey key) && exists
 		then do
 			showStart "migrate" file
diff --git a/Command/PreCommit.hs b/Command/PreCommit.hs
index 57bc7ac13..b0328ca19 100644
--- a/Command/PreCommit.hs
+++ b/Command/PreCommit.hs
@@ -10,7 +10,6 @@ module Command.PreCommit where
 import Command
 import qualified Command.Add
 import qualified Command.Fix
-import Backend
 
 def :: [Command]
 def = [command "pre-commit" paramPaths seek "run by git pre-commit hook"]
@@ -22,12 +21,12 @@ seek =
 	[ withFilesToBeCommitted $ whenAnnexed Command.Fix.start
 	, withFilesUnlockedToBeCommitted start]
 
-start :: BackendFile -> CommandStart
-start p = next $ perform p
+start :: FilePath -> CommandStart
+start file = next $ perform file
 
-perform :: BackendFile -> CommandPerform
-perform pair@(_, file) = do
-	ok <- doCommand $ Command.Add.start pair
+perform :: FilePath -> CommandPerform
+perform file = do
+	ok <- doCommand $ Command.Add.start file
 	if ok
 		then next $ return True
 		else error $ "failed to add " ++ file ++ "; canceling commit"
diff --git a/Git/CheckAttr.hs b/Git/CheckAttr.hs
index 5c747a951..669a9c54e 100644
--- a/Git/CheckAttr.hs
+++ b/Git/CheckAttr.hs
@@ -1,6 +1,6 @@
 {- git check-attr interface
  -
- - Copyright 2010, 2011 Joey Hess <joey@kitenet.net>
+ - Copyright 2010-2012 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -12,20 +12,44 @@ import Git
 import Git.Command
 import qualified Git.Version
 
-{- Efficiently looks up a gitattributes value for each file in a list. -}
-lookup :: String -> [FilePath] -> Repo -> IO [(FilePath, String)]
-lookup attr files repo = do
+type CheckAttrHandle = (PipeHandle, Handle, Handle, [Attr], String)
+
+type Attr = String
+
+{- Starts git check-attr running to look up the specified gitattributes
+ - values and return a handle.  -}
+checkAttrStart :: [Attr] -> Repo -> IO CheckAttrHandle
+checkAttrStart attrs repo = do
 	cwd <- getCurrentDirectory
-	(_, r) <- pipeBoth "git" (toCommand params) $
-		join "\0" $ input cwd
-	return $ zip files $ map attrvalue $ lines r
+	(pid, from, to) <- hPipeBoth "git" $ toCommand $
+		gitCommandLine params repo
+	return (pid, from, to, attrs, cwd)
 	where
-		params = gitCommandLine 
-				[ Param "check-attr"
-				, Param attr
-				, Params "-z --stdin"
-				] repo
+		params =
+			[ Param "check-attr" ]
+			++ map Param attrs ++
+			[ Params "-z --stdin" ]
 
+{- Stops git check-attr. -}
+checkAttrStop :: CheckAttrHandle -> IO ()
+checkAttrStop (pid, from, to, _, _) = do
+	hClose to
+	hClose from
+	forceSuccess pid
+
+{- Gets an attribute of a file. -}
+checkAttr :: CheckAttrHandle -> Attr -> FilePath -> IO String
+checkAttr (_, from, to, attrs, cwd) want file = do
+	hPutStr to $ file' ++ "\0"
+	hFlush to
+	pairs <- forM attrs $ \attr -> do
+		l <- hGetLine from
+		return (attr, attrvalue attr l)
+	let vals = map snd $ filter (\(attr, _) -> attr == want) pairs
+	case vals of
+		[v] -> return v
+		_ -> error $ "unable to determine " ++ want ++ " attribute of " ++ file
+	where
 		{- Before git 1.7.7, git check-attr worked best with
 		 - absolute filenames; using them worked around some bugs
 		 - with relative filenames.
@@ -34,10 +58,10 @@ lookup attr files repo = do
 		 - filenames, and the bugs that necessitated them were fixed,
 		 - so use relative filenames. -}
 		oldgit = Git.Version.older "1.7.7"
-		input cwd
-			| oldgit = map (absPathFrom cwd) files
-			| otherwise = map (relPathDirToFile cwd . absPathFrom cwd) files
-		attrvalue l = end bits !! 0
+		file'
+			| oldgit = absPathFrom cwd file
+			| otherwise = relPathDirToFile cwd $ absPathFrom cwd file
+		attrvalue attr l = end bits !! 0
 			where
 				bits = split sep l
 				sep = ": " ++ attr ++ ": "
diff --git a/Remote/List.hs b/Remote/List.hs
index e589b4401..7c419c75d 100644
--- a/Remote/List.hs
+++ b/Remote/List.hs
@@ -17,7 +17,7 @@ import Annex.UUID
 import Config
 
 import qualified Remote.Git
-import qualified Remote.S3
+--import qualified Remote.S3
 import qualified Remote.Bup
 import qualified Remote.Directory
 import qualified Remote.Rsync
@@ -27,7 +27,7 @@ import qualified Remote.Hook
 remoteTypes :: [RemoteType]
 remoteTypes =
 	[ Remote.Git.remote
-	, Remote.S3.remote
+--	, Remote.S3.remote
 	, Remote.Bup.remote
 	, Remote.Directory.remote
 	, Remote.Rsync.remote
diff --git a/Seek.hs b/Seek.hs
index b4e1218e2..a9c034d22 100644
--- a/Seek.hs
+++ b/Seek.hs
@@ -14,11 +14,9 @@ module Seek where
 import Common.Annex
 import Types.Command
 import Types.Key
-import Backend
 import qualified Annex
 import qualified Git
 import qualified Git.LsFiles as LsFiles
-import qualified Git.CheckAttr
 import qualified Limit
 import qualified Option
 
@@ -28,26 +26,12 @@ seekHelper a params = inRepo $ \g -> runPreserveOrder (`a` g) params
 withFilesInGit :: (FilePath -> CommandStart) -> CommandSeek
 withFilesInGit a params = prepFiltered a $ seekHelper LsFiles.inRepo params
 
-withAttrFilesInGit :: String -> ((FilePath, String) -> CommandStart) -> CommandSeek
-withAttrFilesInGit attr a params = do
-	files <- seekHelper LsFiles.inRepo params
-	prepFilteredGen a fst $ inRepo $ Git.CheckAttr.lookup attr files
-
-withNumCopies :: (Maybe Int -> FilePath -> CommandStart) -> CommandSeek
-withNumCopies a params = withAttrFilesInGit "annex.numcopies" go params
-	where
-		go (file, v) = a (readish v) file
-
-withBackendFilesInGit :: (BackendFile -> CommandStart) -> CommandSeek
-withBackendFilesInGit a params =
-	prepBackendPairs a =<< seekHelper LsFiles.inRepo params
-
-withFilesNotInGit :: (BackendFile -> CommandStart) -> CommandSeek
+withFilesNotInGit :: (FilePath -> CommandStart) -> CommandSeek
 withFilesNotInGit a params = do
 	{- dotfiles are not acted on unless explicitly listed -}
 	files <- filter (not . dotfile) <$> seek ps
 	dotfiles <- if null dotps then return [] else seek dotps
-	prepBackendPairs a $ preserveOrder params (files++dotfiles)
+	prepFiltered a $ return $ preserveOrder params (files++dotfiles)
 	where
 		(dotps, ps) = partition dotfile params
 		seek l = do
@@ -65,20 +49,20 @@ withFilesToBeCommitted :: (String -> CommandStart) -> CommandSeek
 withFilesToBeCommitted a params = prepFiltered a $
 	seekHelper LsFiles.stagedNotDeleted params
 
-withFilesUnlocked :: (BackendFile -> CommandStart) -> CommandSeek
+withFilesUnlocked :: (FilePath -> CommandStart) -> CommandSeek
 withFilesUnlocked = withFilesUnlocked' LsFiles.typeChanged
 
-withFilesUnlockedToBeCommitted :: (BackendFile -> CommandStart) -> CommandSeek
+withFilesUnlockedToBeCommitted :: (FilePath -> CommandStart) -> CommandSeek
 withFilesUnlockedToBeCommitted = withFilesUnlocked' LsFiles.typeChangedStaged
 
-withFilesUnlocked' :: ([FilePath] -> Git.Repo -> IO [FilePath]) -> (BackendFile -> CommandStart) -> CommandSeek
+withFilesUnlocked' :: ([FilePath] -> Git.Repo -> IO [FilePath]) -> (FilePath -> CommandStart) -> CommandSeek
 withFilesUnlocked' typechanged a params = do
 	-- unlocked files have changed type from a symlink to a regular file
 	top <- fromRepo Git.workTree
 	typechangedfiles <- seekHelper typechanged params
-	unlockedfiles <- liftIO $ filterM notSymlink $
+	let unlockedfiles = liftIO $ filterM notSymlink $
 		map (\f -> top ++ "/" ++ f) typechangedfiles
-	prepBackendPairs a unlockedfiles
+	prepFiltered a unlockedfiles
 
 withKeys :: (Key -> CommandStart) -> CommandSeek
 withKeys a params = return $ map (a . parse) params
@@ -109,9 +93,6 @@ withNothing _ _ = error "This command takes no parameters."
 prepFiltered :: (FilePath -> CommandStart) -> Annex [FilePath] -> Annex [CommandStart]
 prepFiltered a = prepFilteredGen a id
 
-prepBackendPairs :: (BackendFile -> CommandStart) -> CommandSeek
-prepBackendPairs a fs = prepFilteredGen a snd (chooseBackends fs)
-
 prepFilteredGen :: (b -> CommandStart) -> (b -> FilePath) -> Annex [b] -> Annex [CommandStart]
 prepFilteredGen a d fs = do
 	matcher <- Limit.getMatcher