safer inannex checking

git-annex-shell inannex now returns always 0, 1, or 100 (the last when
it's unclear if content is currently in the index due to it currently being
moved or dropped).

(Actual locking code still not yet written.)

Remote/Git.hs

@@ -125,22 +125,38 @@ tryGitConfigRead r
 				else old : exchange ls new
 
 {- Checks if a given remote has the content for a key inAnnex.
- - If the remote cannot be accessed, returns a Left error.
+ - If the remote cannot be accessed, or if it cannot determine
+ - whether it has the content, returns a Left error message.
  -}
-inAnnex :: Git.Repo -> Key -> Annex (Either IOException Bool)
+inAnnex :: Git.Repo -> Key -> Annex (Either String Bool)
 inAnnex r key
-	| Git.repoIsHttp r = safely checkhttp
+	| Git.repoIsHttp r = checkhttp
 	| Git.repoIsUrl r = checkremote
-	| otherwise = safely checklocal
+	| otherwise = checklocal
 	where
-		checklocal = onLocal r $ Annex.Content.inAnnex key
+		checkhttp = dispatch <$> check
+			where
+				check = safely $ Url.exists $ keyUrl r key
+				dispatch (Left e) = Left $ show e
+				dispatch (Right v) = Right v
 		checkremote = do
 			showAction $ "checking " ++ Git.repoDescribe r
-			inannex <- onRemote r (boolSystem, False) "inannex" 
-				[Param (show key)]
-			return $ Right inannex
-		checkhttp = Url.exists $ keyUrl r key
-		safely a = liftIO (try a ::IO (Either IOException Bool))
+			onRemote r (check, unknown) "inannex" [Param (show key)]
+			where
+				check c p = dispatch <$> safeSystem c p
+				dispatch ExitSuccess = Right True
+				dispatch (ExitFailure 1) = Right False
+				dispatch _ = unknown
+		checklocal = dispatch <$> check
+			where
+				check = safely $ onLocal r $
+					Annex.Content.inAnnexSafe key
+				dispatch (Left e) = Left $ show e
+				dispatch (Right (Just b)) = Right b
+				dispatch (Right Nothing) = unknown
+		safely :: IO a -> Annex (Either IOException a)
+		safely a = liftIO $ try a
+		unknown = Left $ "unable to check " ++ Git.repoDescribe r
 
 {- Runs an action on a local repository inexpensively, by making an annex
  - monad using that repository. -}