sync: Warn when a remote's export is not updated to the current tree because export tracking is not configured.

Only display the warning when the current branch has a tree that is not
the same as the tree in the export.

Note that it doesn't check to see if the current tree is
in incompleteExportedTreeish; it might be worth checking that and reminding
the user about an incomplete export, but when export tracking is not
configured, they are probably not in the right clone of the repository to
resolve the incomplete export.

This commit was sponsored by Ethan Aubin.

Command/Sync.hs

@@ -189,7 +189,7 @@ seek o = allowConcurrentOutput $ do
 			
 			whenM shouldsynccontent $ do
 				syncedcontent <- seekSyncContent o dataremotes
-				exportedcontent <- seekExportContent exportremotes
+				exportedcontent <- withbranch $ seekExportContent exportremotes
 				-- Transferring content can take a while,
 				-- and other changes can be pushed to the
 				-- git-annex branch on the remotes in the
@@ -680,22 +680,39 @@ syncFile ebloom rs af k = onlyActionOn' k $ do
  - 
  - Returns True if any file transfers were made.
  -}
-seekExportContent :: [Remote] -> Annex Bool
-seekExportContent rs = or <$> forM rs go
+seekExportContent :: [Remote] -> CurrBranch -> Annex Bool
+seekExportContent rs (currbranch, _) = or <$> forM rs go
   where
 	go r = withExclusiveLock (gitAnnexExportLock (Remote.uuid r)) $ do
 		db <- Export.openDb (Remote.uuid r)
 		ea <- Remote.exportActions r
 		exported <- case remoteAnnexExportTracking (Remote.gitconfig r) of
-			Nothing -> getExport (Remote.uuid r)
+			Nothing -> nontracking r
 			Just b -> do
 				mcur <- inRepo $ Git.Ref.tree b
 				case mcur of
-					Nothing -> getExport (Remote.uuid r)
+					Nothing -> nontracking r
 					Just cur -> do
 						Command.Export.changeExport r ea db cur
 						return [Exported cur []]
 		Export.closeDb db `after` fillexport r ea db exported
+		
+	nontracking r = do
+		exported <- getExport (Remote.uuid r)
+		maybe noop (warnnontracking r exported) currbranch
+		return exported
+	
+	warnnontracking r exported currb = inRepo (Git.Ref.tree currb) >>= \case
+		Just currt | not (any (\ex -> exportedTreeish ex == currt) exported) ->
+			showLongNote $ unwords
+				[ "Not updating export to " ++ Remote.name r
+				, "to reflect changes to the tree, because export"
+				, "tracking is not enabled. "
+				, "(Use git-annex export's --tracking option"
+				, "to enable it.)"
+				]
+		_ -> noop
+
 
 	fillexport _ _ _ [] = return False
 	fillexport r ea db (Exported { exportedTreeish = t }:[]) =