change retrieveExport and getKey to throw exception

retrieveExport is part of ongoing transition to make remote methods
throw exceptions, rather than silently hide them.

getKey very rarely fails, and when it does it's always for the same reason
(user configured annex.backend to url for some reason). So, this will
avoid dealing with Nothing everywhere it's used.

This commit was sponsored by Ilya Shlyakhter on Patreon.

Command/AddUrl.hs

@@ -313,7 +313,7 @@ downloadWeb addunlockedmatcher o url urlinfo file =
 	normalfinish tmp = checkCanAdd file $ do
 		showDestinationFile file
 		createWorkTreeDirectory (parentDir file)
-		finishDownloadWith addunlockedmatcher tmp webUUID url file
+		Just <$> finishDownloadWith addunlockedmatcher tmp webUUID url file
 	tryyoutubedl tmp
 		-- Ask youtube-dl what filename it will download
 		-- first, and check if that is already an annexed file,
@@ -388,7 +388,7 @@ downloadWith addunlockedmatcher downloader dummykey u url file =
   where
 	afile = AssociatedFile (Just (toRawFilePath file))
 	go Nothing = return Nothing
-	go (Just tmp) = finishDownloadWith addunlockedmatcher tmp u url file
+	go (Just tmp) = Just <$> finishDownloadWith addunlockedmatcher tmp u url file
 
 {- Like downloadWith, but leaves the dummy key content in
  - the returned location. -}
@@ -404,7 +404,7 @@ downloadWith' downloader dummykey u url afile =
 			then return (Just tmp)
 			else return Nothing
 
-finishDownloadWith :: AddUnlockedMatcher -> FilePath -> UUID -> URLString -> FilePath -> Annex (Maybe Key)
+finishDownloadWith :: AddUnlockedMatcher -> FilePath -> UUID -> URLString -> FilePath -> Annex Key
 finishDownloadWith addunlockedmatcher tmp u url file = do
 	backend <- chooseBackend file
 	let source = KeySource
@@ -412,11 +412,9 @@ finishDownloadWith addunlockedmatcher tmp u url file = do
 		, contentLocation = toRawFilePath tmp
 		, inodeCache = Nothing
 		}
-	genKey source nullMeterUpdate backend >>= \case
-		Nothing -> return Nothing
-		Just (key, _) -> do
-			addWorkTree addunlockedmatcher u url file key (Just tmp)
-			return (Just key)
+	key <- fst <$> genKey source nullMeterUpdate backend
+	addWorkTree addunlockedmatcher u url file key (Just tmp)
+	return key
 
 {- Adds the url size to the Key. -}
 addSizeUrlKey :: Url.UrlInfo -> Key -> Key

Command/CalcKey.hs

@@ -20,11 +20,11 @@ cmd = noCommit $ noMessages $ dontCheck repoExists $
 		(batchable run (pure ()))
 
 run :: () -> String -> Annex Bool
-run _ file = genKey ks nullMeterUpdate Nothing >>= \case
-	Just (k, _) -> do
+run _ file = tryNonAsync (genKey ks nullMeterUpdate Nothing) >>= \case
+	Right (k, _) -> do
 		liftIO $ putStrLn $ serializeKey k
 		return True
-	Nothing -> return False
+	Left _err -> return False
   where
 	ks = KeySource file' file' Nothing
 	file' = toRawFilePath file

Command/Import.hs

@@ -227,10 +227,8 @@ startLocal addunlockedmatcher largematcher mode (srcfile, destfile) =
 		case v of
 			Just ld -> do
 				backend <- chooseBackend destfile
-				v' <- genKey (keySource ld) nullMeterUpdate backend
-				case v' of
-					Just (k, _) -> a (ld, k)
-					Nothing -> giveup "failed to generate a key"
+				k <- fst <$> genKey (keySource ld) nullMeterUpdate backend
+				a (ld, k)
 			Nothing -> stop
 	checkdup k dupa notdupa = ifM (isKnownKey k)
 		( dupa

Command/Migrate.hs

@@ -89,10 +89,8 @@ perform file oldkey oldbackend newbackend = go =<< genkey (fastMigrate oldbacken
 			, contentLocation = content
 			, inodeCache = Nothing
 			}
-		v <- genKey source nullMeterUpdate (Just newbackend)
-		return $ case v of
-			Just (newkey, _) -> Just (newkey, False)
-			_ -> Nothing
+		newkey <- fst <$> genKey source nullMeterUpdate (Just newbackend)
+		return $ Just (newkey, False)
 	genkey (Just fm) = fm oldkey newbackend afile >>= \case
 		Just newkey -> return (Just (newkey, True))
 		Nothing -> genkey Nothing

Command/Reinject.hs

@@ -55,15 +55,13 @@ startSrcDest _ = giveup "specify a src file and a dest file"
 startKnown :: FilePath -> CommandStart
 startKnown src = notAnnexed src $
 	starting "reinject" (ActionItemOther (Just src)) $ do
-		mkb <- genKey ks nullMeterUpdate Nothing
-		case mkb of
-			Nothing -> error "Failed to generate key"
-			Just (key, _) -> ifM (isKnownKey key)
-				( perform src key
-				, do
-					warning "Not known content; skipping"
-					next $ return True
-				)
+		(key, _) <- genKey ks nullMeterUpdate Nothing
+		ifM (isKnownKey key)
+			( perform src key
+			, do
+				warning "Not known content; skipping"
+				next $ return True
+			)
   where
 	ks = KeySource src' src' Nothing
 	src' = toRawFilePath src

Command/TestRemote.hs

@@ -329,10 +329,9 @@ testExportTree runannex mkr mkk1 mkk2 =
 		Remote.storeExport ea loc k testexportlocation nullMeterUpdate
 	retrieveexport ea k = withTmpFile "exported" $ \tmp h -> do
 		liftIO $ hClose h
-		ifM (Remote.retrieveExport ea k testexportlocation tmp nullMeterUpdate)
-			( verifyKeyContent RetrievalAllKeysSecure AlwaysVerify UnVerified k tmp
-			, return False
-			)
+		tryNonAsync (Remote.retrieveExport ea k testexportlocation tmp nullMeterUpdate) >>= \case
+			Left _ -> return False
+			Right () -> verifyKeyContent RetrievalAllKeysSecure AlwaysVerify UnVerified k tmp
 	checkpresentexport ea k = Remote.checkPresentExport ea k testexportlocation
 	removeexport ea k = Remote.removeExport ea k testexportlocation
 	removeexportdirectory ea = case Remote.removeExportDirectory ea of
@@ -405,7 +404,7 @@ randKey :: Int -> Annex Key
 randKey sz = withTmpFile "randkey" $ \f h -> do
 	gen <- liftIO (newGenIO :: IO SystemRandom)
 	case genBytes sz gen of
-		Left e -> error $ "failed to generate random key: " ++ show e
+		Left e -> giveup $ "failed to generate random key: " ++ show e
 		Right (rand, _) -> liftIO $ B.hPut h rand
 	liftIO $ hClose h
 	let ks = KeySource
@@ -413,8 +412,9 @@ randKey sz = withTmpFile "randkey" $ \f h -> do
 		, contentLocation = toRawFilePath f
 		, inodeCache = Nothing
 		}
-	k <- fromMaybe (error "failed to generate random key")
-		<$> Backend.getKey Backend.Hash.testKeyBackend ks nullMeterUpdate
+	k <- case Backend.getKey Backend.Hash.testKeyBackend of
+		Just a -> a ks nullMeterUpdate
+		Nothing -> giveup "failed to generate random key (backend problem)"
 	_ <- moveAnnex k f
 	return k