avoid duplicates building up in outManifest

Happened exponentially since commit 1a3c60cc8e

Types/GitRemoteAnnex.hs

@@ -15,6 +15,7 @@ module Types.GitRemoteAnnex
 import Types.Key
 
 import qualified Data.Semigroup as Sem
+import qualified Data.Set as S
 
 -- The manifest contains an ordered list of git bundle keys.
 --
@@ -24,21 +25,21 @@ import qualified Data.Semigroup as Sem
 data Manifest =
 	Manifest 
 		{ inManifest :: [Key]
-		, outManifest :: [Key]
+		, outManifest :: S.Set Key
 		}
 	deriving (Show)
 
 -- Smart constructor for Manifest. Preserves outManifest invariant.
 mkManifest
 	:: [Key] -- ^ inManifest
-	-> [Key] -- ^ outManifest
+	-> S.Set Key -- ^ outManifest
 	-> Manifest
-mkManifest inks outks = Manifest inks (filter (`notElem` inks) outks)
+mkManifest inks outks = Manifest inks (S.filter (`notElem` inks) outks)
 
 instance Monoid Manifest where
-	mempty = Manifest [] []
+	mempty = Manifest mempty mempty
 
 instance Sem.Semigroup Manifest where
 	a <> b = mkManifest
 		(inManifest a <> inManifest b)
-		(outManifest a <> outManifest b)
+		(S.union (outManifest a) (outManifest b))