export: fix multi-file delete bug

export: Fix a bug that left a file on a special remote when two files with
the same content were both deleted in the exported tree.

Case of the wrong data structure leading to the wrong result.
The DiffMap now contains all the old filenames, and all the new filenames.

Note that, when 2 files with the same content are both renamed,
it only renames the first, but deletes and re-exports the second.
Improving that is possible, but it would need to use a different temporary
filename. Anyway, that is an unusual case, and there are known to be other
unusual cases where export does not rename with maximum efficiency, IIRC.
(Or maybe this is the case that I remember?)

Sponsored-by: Dartmouth College's OpenNeuro project

CHANGELOG

@@ -1,5 +1,7 @@
 git-annex (10.20221104) UNRELEASED; urgency=medium
 
+  * export: Fix a bug that left a file on a special remote when
+    two files with the same content were both deleted in the exported tree.
   * S3: Support signature=anonymous to access a S3 bucket anonymously.
     This can be used, for example, with importtree=yes to import from
     a public bucket.

Command/Export.hs

@@ -149,23 +149,24 @@ changeExport r db (ExportFiltered new) = do
 		[] -> updateExportTree db emptyTree new
 		[oldtreesha] -> do
 			diffmap <- mkDiffMap oldtreesha new db
-			let seekdiffmap a = commandActions $ 
-				map a (M.toList diffmap)
+			let seekdiffmap a = mapM_ a (M.toList diffmap)
 			-- Rename old files to temp, or delete.
-			seekdiffmap $ \(ek, (moldf, mnewf)) -> do
-				case (moldf, mnewf) of
-					(Just oldf, Just _newf) ->
+			let deleteoldf = \ek oldf -> commandAction $
+				startUnexport' r db oldf ek
+			seekdiffmap $ \case
+				(ek, (oldf:oldfs, _newf:_)) -> do
+					commandAction $
 						startMoveToTempName r db oldf ek
-					(Just oldf, Nothing) ->
-						startUnexport' r db oldf ek
-					_ -> stop
+					forM_ oldfs (deleteoldf ek)
+				(ek, (oldfs, [])) ->
+					forM_ oldfs (deleteoldf ek)
+				(_ek, ([], _)) -> noop
 			waitForAllRunningCommandActions
 			-- Rename from temp to new files.
-			seekdiffmap $ \(ek, (moldf, mnewf)) ->
-				case (moldf, mnewf) of
-					(Just _oldf, Just newf) ->
-						startMoveFromTempName r db ek newf
-					_ -> stop
+			seekdiffmap $ \case
+				(ek, (_oldf:_, newf:_)) -> commandAction $
+					startMoveFromTempName r db ek newf
+				_ -> noop
 			waitForAllRunningCommandActions
 		ts -> do
 			warning "Resolving export conflict.."
@@ -204,7 +205,7 @@ changeExport r db (ExportFiltered new) = do
 		void $ liftIO cleanup
 
 -- Map of old and new filenames for each changed Key in a diff.
-type DiffMap = M.Map Key (Maybe TopFilePath, Maybe TopFilePath)
+type DiffMap = M.Map Key ([TopFilePath], [TopFilePath])
 
 mkDiffMap :: Git.Ref -> Git.Ref -> ExportHandle -> Annex DiffMap
 mkDiffMap old new db = do
@@ -213,14 +214,14 @@ mkDiffMap old new db = do
 	void $ liftIO cleanup
 	return diffmap
   where
-	combinedm (srca, dsta) (srcb, dstb) = (srca <|> srcb, dsta <|> dstb)
+	combinedm (srca, dsta) (srcb, dstb) = (srca ++ srcb, dsta ++ dstb)
 	mkdm i = do
 		srcek <- getek (Git.DiffTree.srcsha i)
 		dstek <- getek (Git.DiffTree.dstsha i)
 		updateExportTree' db srcek dstek i
 		return $ catMaybes
-			[ (, (Just (Git.DiffTree.file i), Nothing)) <$> srcek
-			, (, (Nothing, Just (Git.DiffTree.file i))) <$> dstek
+			[ (, ([Git.DiffTree.file i], [])) <$> srcek
+			, (, ([], [Git.DiffTree.file i])) <$> dstek
 			]
 	getek sha
 		| sha `elem` nullShas = return Nothing

doc/bugs/Versioned_S3_tree_does_not_unexport_git_objects.mdwn

@@ -395,3 +395,5 @@ ok
 Thank you for all your work making this wonderful tool!
 
 [[!meta title="export tree bug when two files with the same content both should be removed"]]
+
+> [[fixed|done]] --[[Joey]]