migrate --apply

And avoid migrate --update/--aply migrating when the new key was already
present in the repository, and got dropped. Luckily, the location log
allows distinguishing from the new key never having been present!

That is mostly useful for --apply because otherwise dropped files would
keep coming back until the old objects were reaped as unused. But it
seemed to make sense to also do it for --update. for consistency in edge
cases if nothing else. One case where --update can use it is when one
branch got migrated earlier, and we dropped the file, and now another
branch has migrated the same file.

Sponsored-by: Jack Hill on Patreon

Logs/Location.hs

@@ -21,6 +21,7 @@ module Logs.Location (
 	logStatusAfter,
 	logChange,
 	loggedLocations,
+	loggedPreviousLocations,
 	loggedLocationsHistorical,
 	loggedLocationsRef,
 	parseLoggedLocations,
@@ -79,7 +80,13 @@ logChange _ NoUUID _ = noop
 {- Returns a list of repository UUIDs that, according to the log, have
  - the value of a key. -}
 loggedLocations :: Key -> Annex [UUID]
-loggedLocations = getLoggedLocations currentLogInfo
+loggedLocations = getLoggedLocations presentLogInfo
+
+{- Returns a list of repository UUIDs that the location log indicates
+ - used to have the vale of a key, but no longer do.
+ -}
+loggedPreviousLocations :: Key -> Annex [UUID]
+loggedPreviousLocations = getLoggedLocations notPresentLogInfo
 
 {- Gets the location log on a particular date. -}
 loggedLocationsHistorical :: RefDate -> Key -> Annex [UUID]

Logs/Migrate.hs

@@ -117,15 +117,18 @@ commitMigration = do
 				(asTopFilePath migrationTreeGraftPoint)
 			committedMigration commitsha
 
--- Streams distributed migrations from the git-annex branch that have not
--- been performed here, and runs the provided action on each old and new
--- key pair.
-streamNewDistributedMigrations :: (Key -> Key -> Annex ()) -> Annex ()
-streamNewDistributedMigrations a = do
+-- Streams distributed migrations from the git-annex branch,
+-- and runs the provided action on each old and new key pair.
+--
+-- With the incremental option, only scans as far as the last recorded
+-- migration that this has handled before.
+streamNewDistributedMigrations :: Bool -> (Key -> Key -> Annex ()) -> Annex ()
+streamNewDistributedMigrations incremental a = do
 	void Annex.Branch.update
 	branchsha <- Annex.Branch.getBranch
 	(stoppoint, toskip) <- getPerformedMigrations
-	(l, cleanup) <- inRepo $ getGitLog branchsha stoppoint
+	(l, cleanup) <- inRepo $ getGitLog branchsha
+		(if incremental then stoppoint else Nothing)
 		[fromRawFilePath migrationTreeGraftPoint]
 		-- Need to follow because migrate.tree is grafted in 
 		-- and then deleted, and normally git log stops when a file

Logs/Presence.hs

@@ -17,8 +17,8 @@ module Logs.Presence (
 	addLog',
 	maybeAddLog,
 	readLog,
-	currentLog,
-	currentLogInfo,
+	presentLogInfo,
+	notPresentLogInfo,
 	historicalLogInfo,
 ) where
 
@@ -68,12 +68,13 @@ genLine logstatus loginfo c old = LogLine c' logstatus loginfo
 readLog :: RawFilePath -> Annex [LogLine]
 readLog = parseLog <$$> Annex.Branch.get
 
-{- Reads a log and returns only the info that is still in effect. -}
-currentLogInfo :: RawFilePath -> Annex [LogInfo]
-currentLogInfo file = map info <$> currentLog file
+{- Reads a log and returns only the info that is still present. -}
+presentLogInfo :: RawFilePath -> Annex [LogInfo]
+presentLogInfo file = map info . filterPresent <$> readLog file
 
-currentLog :: RawFilePath -> Annex [LogLine]
-currentLog file = filterPresent <$> readLog file
+{- Reads a log and returns only the info that is no longer present. -}
+notPresentLogInfo :: RawFilePath -> Annex [LogInfo]
+notPresentLogInfo file = map info . filterNotPresent <$> readLog file
 
 {- Reads a historical version of a log and returns the info that was in
  - effect at that time. 

Logs/Presence/Pure.hs

@@ -70,14 +70,18 @@ buildLog = mconcat . map genline
 	genstatus InfoMissing = charUtf8 '0'
 	genstatus InfoDead = charUtf8 'X'
 
-{- Given a log, returns only the info that is are still in effect. -}
+{- Given a log, returns only the info that is still present. -}
 getLog :: L.ByteString -> [LogInfo]
 getLog = map info . filterPresent . parseLog
 
-{- Returns the info from LogLines that are in effect. -}
+{- Returns the info from LogLines that is present. -}
 filterPresent :: [LogLine] -> [LogLine]
 filterPresent = filter (\l -> InfoPresent == status l) . compactLog
 
+{- Returns the info from LogLines that is not present. -}
+filterNotPresent :: [LogLine] -> [LogLine]
+filterNotPresent = filter (\l -> InfoPresent /= status l) . compactLog
+
 {- Compacts a set of logs, returning a subset that contains the current
  - status. -}
 compactLog :: [LogLine] -> [LogLine]

Logs/Web.hs

@@ -55,7 +55,7 @@ getUrls' key = do
   where
 	go [] = return []
 	go (l:ls) = do
-		us <- currentLogInfo l
+		us <- presentLogInfo l
 		if null us
 			then go ls
 			else return $ map fromLogInfo us