fix crashes when run in a git repo that has been initted but has no master branch yet

Assistant/Threads/MountWatcher.hs

@@ -22,8 +22,8 @@ import Utility.ThreadScheduler
 import Utility.Mounts
 import Remote.List
 import qualified Types.Remote as Remote
-import qualified Command.Sync
 import Assistant.Threads.Merger
+import qualified Git.Branch
 
 import Control.Concurrent
 import qualified Control.Exception as E
@@ -161,15 +161,18 @@ handleMount st dstatus scanremotes dir = do
 	debug thisThread ["detected mount of", dir]
 	rs <- remotesUnder st dstatus dir
 	unless (null rs) $ do
-		branch <- runThreadState st $ Command.Sync.currentBranch
-		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
+		go rs =<< runThreadState st (inRepo Git.Branch.current)
+	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
 
 {- Finds remotes located underneath the mount point.
  -

Assistant/Threads/Pusher.hs

@@ -17,6 +17,7 @@ import Assistant.DaemonStatus
 import qualified Command.Sync
 import Utility.ThreadScheduler
 import Utility.Parallel
+import qualified Git.Branch
 
 import Data.Time.Clock
 import qualified Data.Map as M
@@ -84,10 +85,11 @@ shouldPush _now commits
 pushToRemotes :: ThreadName -> UTCTime -> ThreadState -> (Maybe FailedPushMap) -> [Remote] -> IO Bool
 pushToRemotes threadname now st mpushmap remotes = do
 	(g, branch) <- runThreadState st $
-		(,) <$> fromRepo id <*> Command.Sync.currentBranch
+		(,) <$> fromRepo id <*> inRepo Git.Branch.current
 	go True branch g remotes
 	where
-		go shouldretry branch g rs = do
+		go _ Nothing _ _ = return True -- no branch, so nothing to do
+		go shouldretry (Just branch) g rs = do
 			debug threadname
 				[ "pushing to"
 				, show rs
@@ -117,4 +119,4 @@ 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
-			go False branch g rs
+			go False (Just branch) g rs

Command/Sync.hs

@@ -6,8 +6,6 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-{-# LANGUAGE BangPatterns #-}
-
 module Command.Sync where
 
 import Common.Annex
@@ -39,7 +37,7 @@ def = [command "sync" (paramOptional (paramRepeating paramRemote))
 -- syncing involves several operations, any of which can independently fail
 seek :: CommandSeek
 seek rs = do
-	branch <- currentBranch
+	branch <- fromMaybe nobranch <$> inRepo Git.Branch.current
 	remotes <- syncRemotes rs
 	return $ concat
 		[ [ commit ]
@@ -49,11 +47,6 @@ seek rs = do
 		, [ pushLocal branch ]
 		, [ pushRemote remote branch | remote <- remotes ]
 		]
-
-currentBranch :: Annex Git.Ref
-currentBranch = do
-	!branch <- fromMaybe nobranch <$> inRepo Git.Branch.current
-	return branch
 	where
 		nobranch = error "no branch is checked out"
 

Git/Branch.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE BangPatterns #-}
+
 module Git.Branch where
 
 import Common
@@ -12,13 +14,22 @@ import Git
 import Git.Sha
 import Git.Command
 
-{- The currently checked out branch. -}
+{- The currently checked out branch.
+ -
+ - In a just initialized git repo before the first commit,
+ - symbolic-ref will show the master branch, even though that
+ - branch is not created yet. So, this also looks at show-ref HEAD
+ - to double-check.
+ -}
 current :: Repo -> IO (Maybe Git.Ref)
-current r = parse <$> pipeRead [Param "symbolic-ref", Param "HEAD"] r
-	where
-		parse v
-			| null v = Nothing
-			| otherwise = Just $ Git.Ref $ firstLine v
+current r = do
+	branch <- firstLine <$> pipeRead [Param "symbolic-ref", Param "HEAD"] r
+	if null branch
+		then return Nothing
+		else ifM (null <$> pipeRead [Param "show-ref", Param branch] r)
+			( return Nothing
+			, return $ Just $ Git.Ref branch
+			)
 
 {- Checks if the second branch has any commits not present on the first
  - branch. -}