export file renaming

This is seriously super hairy. It has to handle interrupted exports,
which may be resumed with the same or a different tree. It also has to
recover from export conflicts, which could cause the wrong content
to be renamed to a file.

I think this works, or is close to working. See the update to the design
for how it works.

This is definitely not optimal, in that it does more renames than are
necessary. It would probably be worth finding the keys that are really
renamed and only renaming those. But let's get the "simple" approach to
work first..

This commit was supported by the NSF-funded DataLad project.

1 files changed, 132 insertions, 35 deletions

diff --git a/Command/Export.hs b/Command/Export.hs
index 878cda8e3..6090b2603 100644
--- a/Command/Export.hs
+++ b/Command/Export.hs
@@ -67,6 +67,12 @@ exportKey sha = mk <$> catKey sha
 		, keyChunkNum = Nothing
 		}
 
+-- To handle renames which swap files, the exported file is first renamed
+-- to a stable temporary name based on the key.
+exportTempName :: ExportKey -> ExportLocation
+exportTempName ek = ExportLocation $ 
+	".git-annex-tmp-content-" ++ key2file (asKey (ek))
+
 seek :: ExportOptions -> CommandSeek
 seek o = do
 	r <- getParsed (exportRemote o)
@@ -78,23 +84,51 @@ seek o = do
 		-- or tag.
 		inRepo (Git.Ref.tree (exportTreeish o))
 	old <- getExport (uuid r)
-
 	recordExportBeginning (uuid r) new
-	when (length old > 1) $
-		warning "Export conflict detected. Different trees have been exported to the same special remote. Resolving.."
-
 	db <- openDb (uuid r)
 	
-	-- First, diff the old and new trees and delete all changed
-	-- files in the export. Every file that remains in the export will
-	-- have the content from the new treeish.
+	-- Clean up after incomplete export of a tree, in which
+	-- the next block of code below may have renamed some files to
+	-- temp files. Diff from the incomplete tree to the new tree,
+	-- and delete any temp files that the new tree can't use.
+	forM_ (concatMap incompleteExportedTreeish old) $ \incomplete ->
+		mapdiff (startUnexportTempName r db . Git.DiffTree.srcsha) incomplete new
+
+	-- Diff the old and new trees, and delete or rename to new name all
+	-- changed files in the export. After this, every file that remains
+	-- in the export will have the content from the new treeish.
 	-- 
 	-- (Also, when there was an export conflict, this resolves it.)
-	forM_ (map exportedTreeish old) $ \oldtreesha -> do
-		(diff, cleanup) <- inRepo $
-			Git.DiffTree.diffTreeRecursive oldtreesha new
-		seekActions $ pure $ map (startUnexport r db) diff
-		void $ liftIO cleanup
+	case map exportedTreeish old of
+		[] -> return ()
+		[oldtreesha] -> do
+			-- Rename all old files to temp.
+			mapdiff
+				(\diff -> startMoveToTempName r db (Git.DiffTree.file diff) (Git.DiffTree.srcsha diff))
+				oldtreesha new
+			-- Rename from temp to new files.
+			mapdiff (\diff -> startMoveFromTempName r db (Git.DiffTree.dstsha diff) (Git.DiffTree.file diff))
+				new oldtreesha
+			-- Remove all remaining temps.
+			mapdiff
+				(startUnexportTempName r db . Git.DiffTree.srcsha)
+				oldtreesha new
+		ts -> do
+			warning "Export conflict detected. Different trees have been exported to the same special remote. Resolving.."
+			forM_ ts $ \oldtreesha -> do
+				-- Unexport both the srcsha and the dstsha,
+				-- because the wrong content may have
+				-- been renamed to the dstsha due to the
+				-- export conflict.
+				let unexportboth d = 
+					[ Git.DiffTree.srcsha d 
+					, Git.DiffTree.dstsha d
+					]
+				-- Don't rename to temp, because the
+				-- content is unknown; unexport instead.
+				mapdiff
+					(\diff -> startUnexport r db (Git.DiffTree.file diff) (unexportboth diff))
+					oldtreesha new
 
 	-- Waiting until now to record the export guarantees that,
 	-- if this export is interrupted, there are no files left over
@@ -110,6 +144,12 @@ seek o = do
 	void $ liftIO cleanup'
 
 	closeDb db
+  where
+	mapdiff a oldtreesha newtreesha = do
+		(diff, cleanup) <- inRepo $
+			Git.DiffTree.diffTreeRecursive oldtreesha newtreesha
+		seekActions $ pure $ map a diff
+		void $ liftIO cleanup
 
 startExport :: Remote -> ExportHandle -> Git.LsTree.TreeItem -> CommandStart
 startExport r db ti = do
@@ -127,7 +167,7 @@ performExport r db ek contentsha loc = do
 	sent <- case ek of
 		AnnexKey k -> ifM (inAnnex k)
 			( metered Nothing k $ \m -> do
-				let rollback = void $ performUnexport r db ek loc
+				let rollback = void $ performUnexport r db [ek] loc
 				sendAnnex k rollback
 					(\f -> storer f k loc m)
 			, do
@@ -151,32 +191,89 @@ cleanupExport r db ek loc = do
 	logChange (asKey ek) (uuid r) InfoPresent
 	return True
 
-startUnexport :: Remote -> ExportHandle -> Git.DiffTree.DiffTreeItem -> CommandStart
-startUnexport r db diff
-	| Git.DiffTree.srcsha diff /= nullSha = do
-		showStart "unexport" f
-		ek <- exportKey (Git.DiffTree.srcsha diff)
-		next $ performUnexport r db ek loc
-	| otherwise = stop
+startUnexport :: Remote -> ExportHandle -> TopFilePath -> [Git.Sha] -> CommandStart
+startUnexport r db f shas = do
+	eks <- forM (filter (/= nullSha) shas) exportKey
+	if null eks
+		then stop
+		else do
+			showStart "unexport" f'
+			next $ performUnexport r db eks loc
   where
-	loc = ExportLocation $ toInternalGitPath f
-	f = getTopFilePath $ Git.DiffTree.file diff
-
-performUnexport :: Remote -> ExportHandle -> ExportKey -> ExportLocation -> CommandPerform
-performUnexport r db ek loc = do
-	let remover = removeExport $ exportActions r
-	ok <- remover (asKey ek) loc
-	if ok
-		then next $ cleanupUnexport r db ek loc
-		else stop
+	loc = ExportLocation $ toInternalGitPath f'
+	f' = getTopFilePath f
+
+performUnexport :: Remote -> ExportHandle -> [ExportKey] -> ExportLocation -> CommandPerform
+performUnexport r db eks loc = do
+	ifM (allM (\ek -> removeExport (exportActions r) (asKey ek) loc) eks)
+		( next $ cleanupUnexport r db eks loc
+		, stop
+		)
 
-cleanupUnexport :: Remote -> ExportHandle -> ExportKey -> ExportLocation -> CommandCleanup
-cleanupUnexport r db ek loc = do
+cleanupUnexport :: Remote -> ExportHandle -> [ExportKey] -> ExportLocation -> CommandCleanup
+cleanupUnexport r db eks loc = do
 	liftIO $ do
-		removeExportLocation db (asKey ek) loc
+		forM_ eks $ \ek ->
+			removeExportLocation db (asKey ek) loc
 		-- Flush so that getExportLocation sees this and any
 		-- other removals of the key.
 		flushDbQueue db
-	whenM (liftIO $ null <$> getExportLocation db (asKey ek)) $
-		logChange (asKey ek) (uuid r) InfoMissing
+	remaininglocs <- liftIO $ 
+		concat <$> forM eks (\ek -> getExportLocation db (asKey ek))
+	when (null remaininglocs) $
+		forM_ eks $ \ek ->
+			logChange (asKey ek) (uuid r) InfoMissing
+	return True
+
+startUnexportTempName :: Remote -> ExportHandle -> Git.Sha -> CommandStart
+startUnexportTempName r db sha
+	| sha == nullSha = stop
+	| otherwise = do
+		ek <- exportKey sha
+		let loc@(ExportLocation f) = exportTempName ek
+		stopUnless (liftIO $ elem loc <$> getExportLocation db (asKey ek)) $ do
+			showStart "unexport" f
+			next $ performUnexport r db [ek] loc
+
+startMoveToTempName :: Remote -> ExportHandle -> TopFilePath -> Git.Sha -> CommandStart
+startMoveToTempName r db f sha
+	| sha == nullSha = stop
+	| otherwise = do
+		ek <- exportKey sha
+		let tmploc@(ExportLocation tmpf) = exportTempName ek
+		showStart "rename" (f' ++ " -> " ++ tmpf)
+		next $ performRename r db ek loc tmploc
+  where
+	loc = ExportLocation $ toInternalGitPath f'
+	f' = getTopFilePath f
+
+startMoveFromTempName :: Remote -> ExportHandle -> Git.Sha -> TopFilePath -> CommandStart
+startMoveFromTempName r db sha f
+	| sha == nullSha = stop
+	| otherwise = do
+		ek <- exportKey sha
+		stopUnless (liftIO $ elem loc <$> getExportLocation db (asKey ek)) $ do
+			let tmploc@(ExportLocation tmpf) = exportTempName ek
+			showStart "rename" (tmpf ++ " -> " ++ f')
+			next $ performRename r db ek tmploc loc
+  where
+	loc = ExportLocation $ toInternalGitPath f'
+	f' = getTopFilePath f
+
+performRename :: Remote -> ExportHandle -> ExportKey -> ExportLocation -> ExportLocation -> CommandPerform
+performRename r db ek src dest = do
+	ifM (renameExport (exportActions r) (asKey ek) src dest)
+		( next $ cleanupRename db ek src dest
+		-- In case the special remote does not support renaming,
+		-- unexport the src instead.
+		, performUnexport r db [ek] src
+		)
+
+cleanupRename :: ExportHandle -> ExportKey -> ExportLocation -> ExportLocation -> CommandCleanup
+cleanupRename db ek src dest = do
+	liftIO $ do
+		removeExportLocation db (asKey ek) src
+		addExportLocation db (asKey ek) dest
+		-- Flush so that getExportLocation sees this.
+		flushDbQueue db
 	return True