started migrate --update

This is most of the way there, but not quite working.

The layout of migrate.tree/ needs to be changed to follow this approach.
git log will list all the files in tree order, so the new layout needs
to alternate old and new keys. Can that be done? git may not document
tree order, or may not preserve it here.

Alternatively, change to using git log --format=raw and extract
the tree header from that, then use
git diff --raw $tree:migrate.tree/old $tree:migrate.tree/new
That will be a little more expensive, but only when there are lots of
migrations.

Sponsored-by: Joshua Antonishen on Patreon

Git/Log.hs

@@ -10,6 +10,7 @@ module Git.Log where
 import Common
 import Git
 import Git.Command
+import Git.Sha
 
 import Data.Time
 import Data.Time.Clock.POSIX
@@ -28,14 +29,15 @@ data RefChange t = RefChange
 -- run after processing the returned list.
 getGitLog
 	:: Ref
+	-> Maybe Ref
 	-> [FilePath]
 	-> [CommandParam]
-	-> (FilePath -> Maybe t)
+	-> (Sha -> FilePath -> Maybe t)
 	-> Repo
 	-> IO ([RefChange t], IO Bool)
-getGitLog ref fs os fileselector repo = do
+getGitLog ref stopref fs os selector repo = do
 	(ls, cleanup) <- pipeNullSplit ps repo
-	return (parseGitRawLog fileselector (map decodeBL ls), cleanup)
+	return (parseGitRawLog selector (map decodeBL ls), cleanup)
   where
 	ps =
 		[ Param "log"
@@ -45,14 +47,16 @@ getGitLog ref fs os fileselector repo = do
 		, Param "--no-abbrev"
 		, Param "--no-renames"
 		] ++ os ++
-		[ Param (fromRef ref)
+		[ case stopref of
+			Just stopref' -> Param $
+				fromRef stopref' <> ".." <> fromRef ref
+			Nothing -> Param (fromRef ref)
 		, Param "--"
 		] ++ map Param fs 
 
--- The commitinfo is the timestamp of the commit, followed by
--- the commit hash and then the commit's parents, separated by spaces.
+-- The commitinfo is the commit hash followed by its timestamp.
 commitinfoFormat :: String
-commitinfoFormat = "%ct"
+commitinfoFormat = "%H %ct"
 
 -- Parses chunked git log --raw output generated by getGitLog, 
 -- which looks something like:
@@ -69,21 +73,23 @@ commitinfoFormat = "%ct"
 --
 -- The commitinfo is not included before all changelines, so
 -- keep track of the most recently seen commitinfo.
-parseGitRawLog :: (FilePath -> Maybe t) -> [String] -> [RefChange t]
-parseGitRawLog fileselector = parse epoch
+parseGitRawLog :: (Ref -> FilePath -> Maybe t) -> [String] -> [RefChange t]
+parseGitRawLog selector = parse (deleteSha, epoch)
   where
 	epoch = toEnum 0 :: POSIXTime
-	parse oldts ([]:rest) = parse oldts rest
-	parse oldts (c1:c2:rest) = case mrc of
-		Just rc -> rc : parse ts rest
-		Nothing -> parse ts (c2:rest)
+	parse old ([]:rest) = parse old rest
+	parse (oldcommitsha, oldts) (c1:c2:rest) = case mrc of
+		Just rc -> rc : parse (commitsha, ts) rest
+		Nothing -> parse (commitsha, ts) (c2:rest)
 	  where
-		(ts, cl) = case separate (== '\n') c1 of
-			(cl', []) -> (oldts, cl')
-			(tss, cl') -> (parseTimeStamp tss, cl')
+		(commitsha, ts, cl) = case separate (== '\n') c1 of
+			(cl', []) -> (oldcommitsha, oldts, cl')
+			(ci, cl') -> case words ci of
+				(css:tss:[]) -> (Ref (encodeBS css), parseTimeStamp tss, cl')
+				_ -> (oldcommitsha, oldts, cl')
 	  	mrc = do
 			(old, new) <- parseRawChangeLine cl
-			v <- fileselector c2
+			v <- selector commitsha c2
 			return $ RefChange
 				{ changetime = ts
 				, changed = v