handle case of adding populated drive to just created repo

The just created repo has no master branch commits yet. This is now
handled, merging in the master branch from the populated drive.

Assistant/Threads/Merger.hs

@@ -89,7 +89,7 @@ mergeBranch = Git.Merge.mergeNonInteractive . Command.Sync.syncBranch
  - when a push fails, which can happen due to a remote not having pushed
  - changes to us. That could be because it doesn't have us as a remote, or
  - because the assistant is not running there, or other reasons. -}
-manualPull :: Git.Ref -> [Remote] -> Annex ()
+manualPull :: (Maybe Git.Ref) -> [Remote] -> Annex ()
 manualPull currentbranch remotes = do
 	forM_ remotes $ \r ->
 		inRepo $ Git.Command.runBool "fetch" [Param $ Remote.name r]

Assistant/Threads/MountWatcher.hs

@@ -161,18 +161,21 @@ handleMount st dstatus scanremotes dir = do
 	debug thisThread ["detected mount of", dir]
 	rs <- remotesUnder st dstatus dir
 	unless (null rs) $ do
-		go rs =<< runThreadState st (inRepo Git.Branch.current)
+		let nonspecial = filter (Git.repoIsLocal . Remote.repo) rs
+		unless (null nonspecial) $ do
+			void $ alertWhile dstatus (syncMountAlert dir nonspecial) $ do
+				debug thisThread ["syncing with", show rs]
+				sync nonspecial =<< runThreadState st (inRepo Git.Branch.current)
+			addScanRemotes scanremotes nonspecial
 	where
-		go _ Nothing = noop
-		go rs (Just branch) = do
-			let nonspecial = filter (Git.repoIsLocal . Remote.repo) rs
-			unless (null nonspecial) $
-				void $ alertWhile dstatus (syncMountAlert dir nonspecial) $ do
-					debug thisThread ["syncing with", show nonspecial]
-					runThreadState st $ manualPull branch nonspecial
-					now <- getCurrentTime	
-					pushToRemotes thisThread now st Nothing nonspecial
-			addScanRemotes scanremotes rs
+		sync rs (Just branch) = do
+			runThreadState st $ manualPull (Just branch) rs
+			now <- getCurrentTime	
+			pushToRemotes thisThread now st Nothing rs
+		{- No local branch exists yet, but we can try pulling. -}
+		sync rs Nothing = do
+			runThreadState st $ manualPull Nothing rs
+			return True
 
 {- Finds remotes located underneath the mount point.
  -

Assistant/Threads/Pusher.hs

@@ -118,5 +118,5 @@ pushToRemotes threadname now st mpushmap remotes = do
 
 		retry branch g rs = do
 			debug threadname [ "trying manual pull to resolve failed pushes" ]
-			runThreadState st $ manualPull branch rs
+			runThreadState st $ manualPull (Just branch) rs
 			go False (Just branch) g rs