avoid hard linking object from other repository when annex.thin is set

This is simpler and less expensive than checking if the src file has a
link count >= 2, and also is unlocked.

Remote/Git.hs

@@ -672,7 +672,12 @@ commitOnCleanup r a = go `after` a
 						toCommand shellparams
 
 wantHardLink :: Annex Bool
-wantHardLink = (annexHardLink <$> Annex.getGitConfig) <&&> (not <$> isDirect)
+wantHardLink = (annexHardLink <$> Annex.getGitConfig)
+	-- Not direct mode files because they can be modified at any time.
+	<&&> (not <$> isDirect)
+	-- Not unlocked files that are hard linked in the work tree,
+	-- because they can be modified at any time.
+	<&&> (not <$> annexThin <$> Annex.getGitConfig)
 
 -- Copies from src to dest, updating a meter. If the copy finishes
 -- successfully, calls a final check action, which must also succeed, or
@@ -694,7 +699,7 @@ mkCopier remotewanthardlink rsyncparams = do
 #ifndef mingw32_HOST_OS
 	localwanthardlink <- wantHardLink
 	let linker = \src dest -> createLink src dest >> return True
-	ifM (pure (remotewanthardlink || localwanthardlink))
+	ifM (pure (remotewanthardlink || localwanthardlink) <&&> not <$> isDirect)
 		( return $ \src dest p check ->
 			ifM (liftIO (catchBoolIO (linker src dest)))
 				( return (True, Verified)

doc/todo/smudge.mdwn

@@ -2,14 +2,6 @@ git-annex should use smudge/clean filters.
 
 ### implementation todo list
 
-* Interaction with shared clones. Should avoid hard linking from/to a
-  object in a shared clone if either repository has the object unlocked
-  with a hard link in place.
-  (And should avoid unlocking an object with a hard link if it's hard
-  linked to a shared clone, but that's already accomplished because it
-  avoids unlocking an object if it's hard linked at all)
-  **release blocker**
-
 * Reconcile staged changes into the associated files database, whenever
   the database is queried. This is needed to handle eg:
   	git add largefile