pre-commit: Update metadata when committing changes to annexed files within a view.

So the user can now switch to a view and then move files around within it
to manage metadata. For example, moving a file into a new directory
when in the tags=* view adds a tag to it.

Implementation is fairly efficient. One diff-index, which is no more
expensive than the first stage of a git commit, followed by possibly
some cat-file --batch traffic to find the key (when deleting a file).
Very similar to what's done in direct mode when committing. And like
direct mode when updating the WC after a merge, it has to buffer the
diff-tree values in order to make 2 passes over them.

When not in a view, pre-commit now does one extra git symbolic-ref,
which is tiny overhead.

This commit was sponsored by Andrew Eskridge.

Command/PreCommit.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010, 2013 Joey Hess <joey@kitenet.net>
+ - Copyright 2010-2014 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -13,6 +13,13 @@ import Config
 import qualified Command.Add
 import qualified Command.Fix
 import Annex.Direct
+import Annex.View
+import Logs.View
+import Logs.MetaData
+import Types.View
+import Types.MetaData
+
+import qualified Data.Set as S
 
 def :: [Command]
 def = [command "pre-commit" paramPaths seek SectionPlumbing
@@ -27,13 +34,45 @@ seek ps = ifM isDirect
 		withFilesToBeCommitted (whenAnnexed Command.Fix.start) ps
 		-- inject unlocked files into the annex
 		withFilesUnlockedToBeCommitted startIndirect ps
+		-- committing changes to a view updates metadata
+		mv <- currentView
+		case mv of
+			Nothing -> noop
+			Just v -> withViewChanges
+				(addViewMetaData v)
+				(removeViewMetaData v)
 	)
 
 startIndirect :: FilePath -> CommandStart
-startIndirect file = next $ do
-	unlessM (callCommandAction $ Command.Add.start file) $
-		error $ "failed to add " ++ file ++ "; canceling commit"
+startIndirect f = next $ do
+	unlessM (callCommandAction $ Command.Add.start f) $
+		error $ "failed to add " ++ f ++ "; canceling commit"
 	next $ return True
 
 startDirect :: [String] -> CommandStart
 startDirect _ = next $ next $ preCommitDirect
+
+addViewMetaData :: View -> FileView -> Key -> CommandStart
+addViewMetaData v f k = do
+	showStart "metadata" f
+	next $ next $ changeMetaData k $ fromView v f
+
+removeViewMetaData :: View -> FileView -> Key -> CommandStart
+removeViewMetaData v f k = do
+	showStart "metadata" f
+	next $ next $ changeMetaData k $ unsetMetaData $ fromView v f
+
+changeMetaData :: Key -> MetaData -> CommandCleanup
+changeMetaData k metadata = do
+	showMetaDataChange metadata
+	addMetaData k metadata
+	return True
+
+showMetaDataChange :: MetaData -> Annex ()
+showMetaDataChange = showLongNote . unlines . concatMap showmeta . fromMetaData
+  where
+	showmeta (f, vs) = map (showmetavalue f) $ S.toList vs
+	showmetavalue f v = fromMetaField f ++ showset v ++ "=" ++ fromMetaValue v
+	showset v
+		| isSet v = "+"
+		| otherwise = "-"