pre-commit: Update direct mode mappings.

Making the pre-commit hook look at git diff-index to find changed direct
mode files and update the mappings works pretty well.

One case where it does not work is when a file is git annex added, and then
git rmed, and then this is committed. That's a no-op commit, so the hook
probably doesn't even run, and it certianly never notices that the file
was deleted, so the mapping will still have the original filename in it.

For this and other reasons, it's important that the mappings still be
treated as possibly inconsistent.

Also, the assistant now allows the pre-commit hook to run when in direct
mode, so the mappings also get updated there.

Command/PreCommit.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010 Joey Hess <joey@kitenet.net>
+ - Copyright 2010, 2013 Joey Hess <joey@kitenet.net>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -11,22 +11,42 @@ import Common.Annex
 import Command
 import qualified Command.Add
 import qualified Command.Fix
+import qualified Git.DiffTree
+import Annex.CatFile
+import Annex.Content.Direct
+import Git.Sha
 
 def :: [Command]
 def = [command "pre-commit" paramPaths seek "run by git pre-commit hook"]
 
-{- The pre-commit hook needs to fix symlinks to all files being committed.
- - And, it needs to inject unlocked files into the annex. -}
 seek :: [CommandSeek]
 seek =
+	-- fix symlinks to files being committed
 	[ whenNotDirect $ withFilesToBeCommitted $ whenAnnexed $ Command.Fix.start
-	, whenNotDirect $ withFilesUnlockedToBeCommitted start]
+	-- inject unlocked files into the annex
+	, whenNotDirect $ withFilesUnlockedToBeCommitted startIndirect
+	-- update direct mode mappings for committed files
+	, whenDirect $ withWords startDirect
+	]
 
-start :: FilePath -> CommandStart
-start file = next $ perform file
-
-perform :: FilePath -> CommandPerform
-perform file = do
+startIndirect :: FilePath -> CommandStart
+startIndirect file = next $ do
 	unlessM (doCommand $ Command.Add.start file) $
 		error $ "failed to add " ++ file ++ "; canceling commit"
 	next $ return True
+
+startDirect :: [String] -> CommandStart
+startDirect _ = next $ do
+	(diffs, clean) <- inRepo $ Git.DiffTree.diffIndex
+	forM_ diffs go
+	next $ liftIO clean
+  where
+	go diff = do
+		withkey (Git.DiffTree.srcsha diff) removeAssociatedFile
+		withkey (Git.DiffTree.dstsha diff) addAssociatedFile
+	  where
+		withkey sha a = when (sha /= nullSha) $ do
+			k <- catKey sha
+			case k of
+				Nothing -> noop
+				Just key -> void $ a key (Git.DiffTree.file diff)