handle Annex.Branch.files with read-only unmerged git-annex branches

It would be difficult to make Annex.Branch.files query the unmerged
git-annex branches. Might be possible, similar to what was discussed in
7f6b2ca49c but again I decided to make it
not do anything in that situation to start with before adding such a
complicated thing.

git-annex info uses it when getting info about a repostory. The choices
were to make that fail with an error, or display the info it can, and
change the output slightly for the bits of info it cannot access. While
that is a behavior change, and I want to avoid any behavior changes due
to unmerged git-annex branches in a read-only repo, displaying a message
that is not a number seems unlikely to break anything that was consuming
a number, any worse than throwing an exception would. Probably.

Also git-annex unused --from origin is made to throw an error, but
it would fail later anyway when trying to write to the unused log files.

Sponsored-by: Dartmouth College's Datalad project

Annex/Branch.hs

@@ -468,16 +468,28 @@ commitIndex' jl branchref message basemessage retrynum parents = do
 		commitIndex' jl committedref racemessage basemessage retrynum' [committedref]
 
 {- Lists all files on the branch. including ones in the journal
- - that have not been committed yet. There may be duplicates in the list. -}
-files :: Annex ([RawFilePath], IO Bool)
+ - that have not been committed yet. 
+ -
+ - There may be duplicates in the list, when the journal has files that
+ - have not been written to the branch yet.
+ - 
+ - In a read-only repository that has other git-annex branches that have
+ - not been merged in, returns Nothing, because it's not possible to
+ - efficiently handle that.
+ -}
+files :: Annex (Maybe ([RawFilePath], IO Bool))
 files = do
-	_  <- update
-	(bfs, cleanup) <- branchFiles
-	-- ++ forces the content of the first list to be buffered in
-	-- memory, so use journalledFiles, which should be much smaller
-	-- most of the time. branchFiles will stream as the list is consumed.
-	l <- (++) <$> journalledFiles <*> pure bfs
-	return (l, cleanup)
+	st <- update
+        if not (null (unmergedRefs st))
+		then return Nothing
+		else do
+			(bfs, cleanup) <- branchFiles
+			-- ++ forces the content of the first list to be
+			-- buffered in memory, so use journalledFiles,
+			-- which should be much smaller most of the time.
+			-- branchFiles will stream as the list is consumed.
+			l <- (++) <$> journalledFiles <*> pure bfs
+			return (Just (l, cleanup))
 
 {- Lists all files currently in the journal. There may be duplicates in
  - the list when using a private journal. -}

Assistant/DeleteRemote.hs

@@ -53,14 +53,14 @@ removeRemote uuid = do
  - in keys in the current branch.
  -}
 removableRemote :: UrlRenderer -> UUID -> Assistant ()
-removableRemote urlrenderer uuid = do
-	keys <- getkeys
-	if null keys
-		then finishRemovingRemote urlrenderer uuid
-		else do
+removableRemote urlrenderer uuid = getkeys >>= \case
+	Just keys
+		| null keys -> finishRemovingRemote urlrenderer uuid
+		| otherwise -> do
 			r <- fromMaybe (error "unknown remote")
 				<$> liftAnnex (Remote.remoteFromUUID uuid)
 			mapM_ (queueremaining r) keys
+	Nothing -> noop
   where
 	queueremaining r k = 
 		queueTransferWhenSmall "remaining object in unwanted remote"

Command/Info.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2011-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -370,13 +370,17 @@ local_annex_size = simpleStat "local annex size" $
 
 -- "remote" is in the name for JSON backwards-compatibility
 repo_annex_keys :: UUID -> Stat
-repo_annex_keys u = stat "remote annex keys" $ json show $
-	countKeys <$> cachedRemoteData u
+repo_annex_keys u = stat "remote annex keys" $ \d ->
+	cachedRemoteData u >>= \case
+		Right rd -> json show (pure (countKeys rd)) d
+		Left n-> json id (pure n) d
 
 -- "remote" is in the name for JSON backwards-compatibility
 repo_annex_size :: UUID -> Stat
 repo_annex_size u = simpleStat "remote annex size" $
-	showSizeKeys =<< cachedRemoteData u
+	cachedRemoteData u >>= \case
+		Right d -> showSizeKeys d
+		Left n -> pure n
 
 known_annex_files :: Bool -> Stat
 known_annex_files isworktree = 
@@ -524,20 +528,22 @@ cachedPresentData = do
 			put s { presentData = Just v }
 			return v
 
-cachedRemoteData :: UUID -> StatState KeyInfo
+cachedRemoteData :: UUID -> StatState (Either String KeyInfo)
 cachedRemoteData u = do
 	s <- get
 	case M.lookup u (repoData s) of
-		Just v -> return v
+		Just v -> return (Right v)
 		Nothing -> do
 			let combinedata d uk = finishCheck uk >>= \case
 				Nothing -> return d
 				Just k -> return $ addKey k d
-			(ks, cleanup) <- lift $ loggedKeysFor' u
-			v <- lift $ foldM combinedata emptyKeyInfo ks
-			liftIO $ void cleanup
-			put s { repoData = M.insert u v (repoData s) }
-			return v
+			lift (loggedKeysFor' u) >>= \case
+				Just (ks, cleanup) -> do
+					v <- lift $ foldM combinedata emptyKeyInfo ks
+					liftIO $ void cleanup
+					put s { repoData = M.insert u v (repoData s) }
+					return (Right v)
+				Nothing -> return (Left "not available in this read-only repository with unmerged git-annex branches")
 
 cachedReferencedData :: StatState KeyInfo
 cachedReferencedData = do

Command/Unused.hs

@@ -101,7 +101,9 @@ checkRemoteUnused remotename refspec = go =<< Remote.nameToUUID remotename
 		r <- Remote.byUUID u
 		_ <- check "" (remoteUnusedMsg r remotename) (remoteunused u) 0
 		next $ return True
-	remoteunused u = excludeReferenced refspec =<< loggedKeysFor u
+	remoteunused u = loggedKeysFor u >>= \case
+		Just ks -> excludeReferenced refspec ks
+		Nothing -> giveup "This repository is read-only."
 
 check :: FilePath -> ([(Int, Key)] -> String) -> Annex [Key] -> Int -> Annex Int
 check file msg a c = do

Logs/Location.hs

@@ -137,15 +137,17 @@ finishCheck (Unchecked a) = a
  -
  - Keys that have been marked as dead are not included.
  -}
-loggedKeys :: Annex ([Unchecked Key], IO Bool)
+loggedKeys :: Annex (Maybe ([Unchecked Key], IO Bool))
 loggedKeys = loggedKeys' (not <$$> checkDead)
 
-loggedKeys' :: (Key -> Annex Bool) -> Annex ([Unchecked Key], IO Bool)
+loggedKeys' :: (Key -> Annex Bool) -> Annex (Maybe ([Unchecked Key], IO Bool))
 loggedKeys' check = do
 	config <- Annex.getGitConfig
-	(bfs, cleanup) <- Annex.Branch.files
-	let l = mapMaybe (defercheck <$$> locationLogFileKey config) bfs
-	return (l, cleanup)
+	Annex.Branch.files >>= \case
+		Nothing -> return Nothing
+		Just (bfs, cleanup) -> do
+			let l = mapMaybe (defercheck <$$> locationLogFileKey config) bfs
+			return (Just (l, cleanup))
   where
 	defercheck k = Unchecked $ ifM (check k)
 		( return (Just k)
@@ -157,14 +159,15 @@ loggedKeys' check = do
  -
  - This does not stream well; use loggedKeysFor' for lazy streaming.
  -}
-loggedKeysFor :: UUID -> Annex [Key]
-loggedKeysFor u = do
-	(l, cleanup) <- loggedKeysFor' u
-	l' <- catMaybes <$> mapM finishCheck l
-	liftIO $ void cleanup
-	return l'
+loggedKeysFor :: UUID -> Annex (Maybe [Key])
+loggedKeysFor u = loggedKeysFor' u >>= \case
+	Nothing -> return Nothing
+	Just (l, cleanup) -> do
+		l' <- catMaybes <$> mapM finishCheck l
+		liftIO $ void cleanup
+		return (Just l')
 
-loggedKeysFor' :: UUID -> Annex ([Unchecked Key], IO Bool)
+loggedKeysFor' :: UUID -> Annex (Maybe ([Unchecked Key], IO Bool))
 loggedKeysFor' u = loggedKeys' isthere
   where
 	isthere k = do