revert change that broke test_readonly

commit 63d508e885 broke test_readonly.
When a local git remote is readonly, tryCopyCoW run to copy a file
from it failed at withOtherTmp.

Sponsored-by: Dartmouth College's Datalad project

Annex/CopyFile.hs

@@ -15,8 +15,6 @@ import Utility.CopyFile
 import Utility.FileMode
 import Utility.Touch
 import Utility.Hash (IncrementalVerifier(..))
-import Annex.Tmp
-import Utility.Tmp
 
 import Control.Concurrent
 import qualified Data.ByteString as S
@@ -30,34 +28,23 @@ newCopyCoWTried :: IO CopyCoWTried
 newCopyCoWTried = CopyCoWTried <$> newEmptyMVar
 
 {- Copies a file is copy-on-write is supported. Otherwise, returns False. -}
-tryCopyCoW :: CopyCoWTried -> FilePath -> FilePath -> MeterUpdate -> Annex Bool
+tryCopyCoW :: CopyCoWTried -> FilePath -> FilePath -> MeterUpdate -> IO Bool
 tryCopyCoW (CopyCoWTried copycowtried) src dest meterupdate =
 	-- If multiple threads reach this at the same time, they
 	-- will both try CoW, which is acceptable.
-	ifM (liftIO $ isEmptyMVar copycowtried)
+	ifM (isEmptyMVar copycowtried)
 		( do
 			ok <- docopycow
-			void $ liftIO $ tryPutMVar copycowtried ok
+			void $ tryPutMVar copycowtried ok
 			return ok
-		, ifM (liftIO $ readMVar copycowtried)
+		, ifM (readMVar copycowtried)
 			( docopycow
 			, return False
 			)
 		)
   where
-	-- copyCow needs a destination file that does not exist,
-	-- but the dest file might already. So use it with another
-	-- temp file, and if it succeeds, rename it into place. If it fails,
-	-- the dest file is left as-is, to support resuming.
-	docopycow = withOtherTmp $ \othertmp -> liftIO $
-		withTmpFileIn (fromRawFilePath othertmp) (takeFileName dest) $ \tmpdest _h -> do
-			copied <- watchFileSize tmpdest meterupdate $
-				copyCoW CopyTimeStamps src tmpdest
-			if copied
-				then liftIO $ catchBoolIO $ do
-					rename tmpdest dest
-					return True
-				else return False
+	docopycow = watchFileSize dest meterupdate $
+		copyCoW CopyTimeStamps src dest
 
 data CopyMethod = CopiedCoW | Copied
 
@@ -83,7 +70,7 @@ fileCopier :: CopyCoWTried -> FilePath -> FilePath -> MeterUpdate -> Maybe Incre
 fileCopier _ src dest meterupdate iv = docopy
 #else
 fileCopier copycowtried src dest meterupdate iv =
-	ifM (tryCopyCoW copycowtried src dest meterupdate)
+	ifM (liftIO $ tryCopyCoW copycowtried src dest meterupdate)
 		( do
 			liftIO $ maybe noop unableIncremental iv
 			return CopiedCoW

CHANGELOG

@@ -8,8 +8,6 @@ git-annex (8.20210904) UNRELEASED; urgency=medium
     (Reversion in version 4.20130323)
   * borg: Avoid trying to extract xattrs, ACLS, and bsdflags when
     retrieving from a borg repository.
-  * Resume where it left off when copying a file to/from a local git remote
-    was interrupted.
   * Sped up git-annex smudge --clean by 25%.
 
  -- Joey Hess <id@joeyh.name>  Fri, 03 Sep 2021 12:02:55 -0400

Remote/Directory.hs

@@ -412,7 +412,7 @@ retrieveExportWithContentIdentifierM dir cow loc cid dest mkkey p =
 	f = exportPath dir loc
 	f' = fromRawFilePath f
 
-	docopy = ifM (tryCopyCoW cow f' dest p)
+	docopy = ifM (liftIO $ tryCopyCoW cow f' dest p)
 		( do
 			k <- mkkey
 			postcheckcow (return k)

Utility/CopyFile.hs

@@ -56,13 +56,11 @@ copyFileExternal meta src dest = do
 		| otherwise = copyMetaDataParams meta
 
 {- When a filesystem supports CoW (and cp does), uses it to make
- - an efficient copy of a file. Otherwise, returns False.
- -
- - The dest file must not exist yet, or it will fail to make a CoW copy,
- - and will return False. -}
+ - an efficient copy of a file. Otherwise, returns False. -}
 copyCoW :: CopyMetaData -> FilePath -> FilePath -> IO Bool
 copyCoW meta src dest
 	| BuildInfo.cp_reflink_supported = do
+		void $ tryIO $ removeFile dest
 		-- When CoW is not supported, cp will complain to stderr,
 		-- so have to discard its stderr.
 		ok <- catchBoolIO $ withNullHandle $ \nullh ->