updatecluster: support multiple gateways

Just look at the existing proxied remotes that correspond to already
existing nodes of the cluster, and keep those nodes in the cluster.
While adding any remotes of the local repo that are configured as
cluster nodes. This allows removing cluster nodes from the local repo
and updating, without it also removing nodes provided by other gateways.

Command/UpdateCluster.hs

@@ -50,23 +50,35 @@ start = startingCustomOutput (ActionItemOther Nothing) $ do
 		let mynodes = S.map (ClusterNodeUUID . R.uuid) mynodesremotes
 		let recordednodes = fromMaybe mempty $ M.lookup cu $
 			clusterUUIDs recordedclusters
-		if recordednodes == mynodes
+		proxiednodes <- findProxiedNodes recordednodes 
+		let allnodes = S.union mynodes proxiednodes
+		if recordednodes == allnodes
 			then liftIO $ putStrLn $ safeOutput $
 				"No cluster node changes for cluster: " ++ clustername
 			else do
-				describechanges descs clustername recordednodes mynodes mynodesremotes
-				recordCluster cu mynodes
+				describechanges descs clustername recordednodes allnodes mynodesremotes
+				recordCluster cu allnodes
 
 	next $ return True
   where
-	describechanges descs clustername oldnodes mynodes mynodesremotes = do
+	describechanges descs clustername oldnodes allnodes mynodesremotes = do
 		forM_ (S.toList mynodesremotes) $ \r ->
 			unless (S.member (ClusterNodeUUID (R.uuid r)) oldnodes) $
 				liftIO $ putStrLn $ safeOutput $
 					"Added node " ++ R.name r ++ " to cluster: " ++ clustername
 		forM_ (S.toList oldnodes) $ \n ->
-			unless (S.member n mynodes) $ do
+			unless (S.member n allnodes) $ do
 				let desc = maybe (fromUUID (fromClusterNodeUUID n)) fromUUIDDesc $
 					M.lookup (fromClusterNodeUUID n) descs
 				liftIO $ putStrLn $ safeOutput $
 					"Removed node " ++ desc ++ " from cluster: " ++ clustername
+
+-- Finds nodes that are proxied by other cluster gateways.
+findProxiedNodes :: S.Set ClusterNodeUUID -> Annex (S.Set ClusterNodeUUID)
+findProxiedNodes recordednodes =
+	(S.fromList . map asclusternode . filter isproxynode) <$> R.remoteList
+  where
+	isproxynode r = 
+		asclusternode r `S.member` recordednodes
+			&& remoteAnnexProxied (R.gitconfig r)
+	asclusternode = ClusterNodeUUID . R.uuid