assistant: Fix bug that could cause incoming pushes to not get merged into the local tree.

Observed that the pushed refs were received, but not merged into master.
The merger never saw an add event for these refs. Either git is not writing
to a new file and renaming it into place, or the inotify code didn't notice
that. Changed it to also watch for modify events and that seems to have
fixed it!

Assistant/Threads/Merger.hs

@@ -32,10 +32,11 @@ mergeThread = namedThread "Merger" $ do
 	let dir = Git.localGitDir g </> "refs"
 	liftIO $ createDirectoryIfMissing True dir
 	let hook a = Just <$> asIO2 (runHandler a)
-	addhook <- hook onAdd
+	changehook <- hook onChange
 	errhook <- hook onErr
 	let hooks = mkWatchHooks
-		{ addHook = addhook
+		{ addHook = changehook
+		, modifyHook = changehook
 		, errHook = errhook
 		}
 	void $ liftIO $ watchDir dir (const False) hooks id
@@ -55,19 +56,14 @@ runHandler handler file _filestatus =
 onErr :: Handler
 onErr msg = error msg
 
-{- Called when a new branch ref is written.
- -
- - This relies on git's atomic method of updating branch ref files,
- - which is to first write the new file to .lock, and then rename it
- - over the old file. So, ignore .lock files, and the rename ensures
- - the watcher sees a new file being added on each update.
+{- Called when a new branch ref is written, or a branch ref is modified.
  -
  - At startup, synthetic add events fire, causing this to run, but that's
  - ok; it ensures that any changes pushed since the last time the assistant
  - ran are merged in.
  -}
-onAdd :: Handler
-onAdd file
+onChange :: Handler
+onChange file
 	| ".lock" `isSuffixOf` file = noop
 	| isAnnexBranch file = do
 		branchChanged
@@ -75,7 +71,7 @@ onAdd file
 		when diverged $
 			unlessM handleDesynced $
 				queueDeferredDownloads "retrying deferred download" Later
-	| "/synced/" `isInfixOf` file = do
+	| "/synced/" `isInfixOf` file =
 		mergecurrent =<< liftAnnex (inRepo Git.Branch.current)
 	| otherwise = noop
   where

debian/changelog

@@ -53,6 +53,8 @@ git-annex (4.20130418) UNRELEASED; urgency=low
     when you or the friend have multiple reposotories on an XMPP account.
     Note that XMPP pairing with your own devices still pairs with all
     repositories using your XMPP account.
+  * assistant: Fix bug that could cause incoming pushes to not get
+    merged into the local tree.
 
  -- Joey Hess <joeyh@debian.org>  Thu, 18 Apr 2013 16:22:48 -0400