add forget command

Works, more or less. --dead is not implemented, and so far a new branch
is made, but keys no longer present anywhere are not scrubbed.

git annex sync fails to push the synced/git-annex branch after a forget,
because it's not a fast-forward of the existing synced branch. Could be
fixed by making git-annex sync use assistant-style sync branches.

Annex/Branch.hs

@@ -402,6 +402,7 @@ handleTransitions :: Transitions -> [Git.Ref] -> Annex (Maybe (Git.Branch, [Git.
 handleTransitions localts refs = do
 	m <- M.fromList <$> mapM getreftransition refs
 	let remotets = M.elems m
+	liftIO $ print ("transitions", localts, remotets)
 	if all (localts ==) remotets
 		then return Nothing
 		else do

Command/Forget.hs

@@ -0,0 +1,41 @@
+{- git-annex command
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Command.Forget where
+
+import Common.Annex
+import Command
+import qualified Annex.Branch as Branch
+import Logs.Transitions
+import qualified Annex
+
+import Data.Time.Clock.POSIX
+
+def :: [Command]
+def = [command "forget" paramNothing seek
+		SectionMaintenance "prune git-annex branch history"]
+
+seek :: [CommandSeek]
+seek = [withNothing start]
+
+start :: CommandStart
+start = do
+	showStart "forget" "git-annex"
+	next $ perform =<< Annex.getState Annex.force
+
+perform :: Bool -> CommandPerform
+perform True = do
+	now <- liftIO getPOSIXTime
+	let ts = addTransition now ForgetGitHistory noTransitions
+	recordTransitions Branch.change ts
+	-- get branch committed before contining with the transition
+	Branch.update
+	void $ Branch.performTransitions ts True
+	next $ return True
+perform False = do
+	showLongNote "To forget git-annex branch history, you must specify --force. This deletes metadata!"
+	stop

GitAnnex.hs

@@ -67,6 +67,7 @@ import qualified Command.Map
 import qualified Command.Direct
 import qualified Command.Indirect
 import qualified Command.Upgrade
+import qualified Command.Forget
 import qualified Command.Version
 import qualified Command.Help
 #ifdef WITH_ASSISTANT
@@ -139,6 +140,7 @@ cmds = concat
 	, Command.Direct.def
 	, Command.Indirect.def
 	, Command.Upgrade.def
+	, Command.Forget.def
 	, Command.Version.def
 	, Command.Help.def
 #ifdef WITH_ASSISTANT

Logs/Transitions.hs

@@ -50,6 +50,9 @@ describeTransition :: Transition -> String
 describeTransition ForgetGitHistory = "forget git history"
 describeTransition ForgetDeadRemotes = "forget dead remotes"
 
+noTransitions :: Transitions
+noTransitions = S.empty
+
 addTransition :: POSIXTime -> Transition -> Transitions -> Transitions
 addTransition ts t = S.insert $ TransitionLine ts t
 
@@ -91,8 +94,7 @@ transitionList = map transition . S.elems
 
 {- Typically ran with Annex.Branch.change, but we can't import Annex.Branch
  - here since it depends on this module. -}
-recordTransition :: (FilePath -> (String -> String) -> Annex ()) -> Transition -> Annex ()
+recordTransitions :: (FilePath -> (String -> String) -> Annex ()) -> Transitions -> Annex ()
-recordTransition changer o = do
+recordTransitions changer t = do
-	t <- liftIO getPOSIXTime
 	changer transitionsLog $
-		showTransitions . addTransition t o . parseTransitionsStrictly "local"
+		showTransitions . S.union t . parseTransitionsStrictly "local"

doc/git-annex.mdwn

@@ -488,7 +488,7 @@ subdirectories).
   be located.
   
   To also prune references to remotes that have been marked as dead,
-  specify --forget-dead.
+  specify --dead.
 
   When this rewritten branch is merged into other clones of
   the repository, git-annex will automatically perform the same rewriting