sync: import when annex-tracking-branch is configured

This works, and tested syncing both gets changes from a special remote
and sends changes to it, keeping it fully in sync nicely!

But have not tried it with a subdir configured.

Command/Import.hs

@@ -104,12 +104,12 @@ seek o@(LocalImportOptions {}) = allowConcurrentOutput $ do
 		`withPathContents` importFiles o
 seek o@(RemoteImportOptions {}) = allowConcurrentOutput $ do
 	r <- getParsed (importFromRemote o)
+	unlessM (Remote.isImportSupported r) $
+		giveup "That remote does not support imports."
 	subdir <- maybe
 		(pure Nothing)
 		(Just <$$> inRepo . toTopFilePath)
 		(importToSubDir o)
-	unlessM (Remote.isImportSupported remote) $
-		giveup "That remote does not support imports."
 	seekRemote r (importToBranch o) subdir
 
 startLocal :: GetFileMatcher -> DuplicateMode -> (FilePath, FilePath) -> CommandStart

Command/Sync.hs

@@ -39,6 +39,7 @@ import qualified Git.Merge
 import qualified Git.Types as Git
 import qualified Git.Ref
 import qualified Git
+import Git.FilePath
 import qualified Remote.Git
 import Config
 import Config.GitConfig
@@ -171,6 +172,7 @@ seek o = allowConcurrentOutput $ do
 	dataremotes <- filter (\r -> Remote.uuid r /= NoUUID)
 		<$> filterM (not <$$> liftIO . getDynamicConfig . remoteAnnexIgnore . Remote.gitconfig) remotes
 	let exportremotes = filter (exportTree . Remote.config) dataremotes
+	let importremotes = filter (importTree . Remote.config) dataremotes
 
 	if cleanupOption o
 		then do
@@ -189,9 +191,11 @@ seek o = allowConcurrentOutput $ do
 				]
 				
 			whenM shouldsynccontent $ do
-				-- Send content to any exports first, in 
-				-- case that lets content be dropped from
-				-- other repositories.
+				mapM_ (withbranch . importRemote o mergeConfig) importremotes
+			
+				-- Send content to any exports before other
+				-- repositories, in case that lets content
+				-- be dropped from other repositories.
 				exportedcontent <- withbranch $
 					seekExportContent (Just o) exportremotes
 				syncedcontent <- withbranch $
@@ -225,10 +229,11 @@ mergeConfig :: [Git.Merge.MergeConfig]
 mergeConfig = 
 	[ Git.Merge.MergeNonInteractive
 	-- In several situations, unrelated histories should be merged
-	-- together. This includes pairing in the assistant, and merging
-	-- from a remote into a newly created direct mode repo.
+	-- together. This includes pairing in the assistant, merging
+	-- from a remote into a newly created direct mode repo,
+	-- and an initial merge from an import from a special remote.
 	-- (Once direct mode is removed, this could be changed, so only
-	-- the assistant uses it.)
+	-- the assistant and import from special remotes use it.)
 	, Git.Merge.MergeUnrelatedHistories
 	]
 
@@ -404,6 +409,23 @@ pullRemote o mergeconfig remote branch = stopUnless (pure $ pullOption o && want
 				[Param "fetch", Param $ Remote.name remote]
 	wantpull = remoteAnnexPull (Remote.gitconfig remote)
 
+importRemote :: SyncOptions -> [Git.Merge.MergeConfig] -> Remote -> CurrBranch -> CommandSeek
+importRemote o mergeconfig remote currbranch
+	| not (pullOption o) || not wantpull = noop
+	| otherwise = case remoteAnnexTrackingBranch (Remote.gitconfig remote) of
+		Nothing -> noop
+		Just tb -> do
+			let (b, s) = separate (== ':') (Git.fromRef tb)
+			let branch = Git.Ref b
+			let subdir = if null s
+				then Nothing
+				else Just (asTopFilePath s)
+			Command.Import.seekRemote remote branch subdir
+			void $ mergeRemote remote currbranch mergeconfig
+				(resolveMergeOverride o)
+  where
+	wantpull = remoteAnnexPull (Remote.gitconfig remote)
+
 {- The remote probably has both a master and a synced/master branch.
  - Which to merge from? Well, the master has whatever latest changes
  - were committed (or pushed changes, if this is a bare remote),

doc/todo/import_tree.mdwn

@@ -10,6 +10,16 @@ this.
 
 ## implementation notes
 
+* renameExport is disabled in a way that makes export tree
+  complain unncessarily verbosely. Perhaps change renameExport
+  to a Maybe so it can know when it's not available.
+
+* Does export of master:subdir update the remote tracking branch right?
+
+* Does sync --content with remote.name.annex-tracking-branch=master:subdir
+  export the right tree and update the remote tracking branch right?
+  Does it import correctly?
+
 * Need to support annex-tracking-branch configuration, which documentation
   says makes git-annex sync and assistant do imports.