config: New command for storing configuration in the git-annex branch.

Any config names can be set using this; git-annex commands will only look
at specific ones that make sense and are worth the overhead of querying the
branch.

This might also be useful for storing whatever other config-type stuff the
user might want to shove into the git-annex branch.

This commit was sponsored by Jochen Bartl on Patreon.

Command/Config.hs

@@ -0,0 +1,65 @@
+{- git-annex command
+ -
+ - Copyright 2017 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Command.Config where
+
+import Command
+import Logs.Config
+
+cmd :: Command
+cmd = command "config" SectionSetup "configuration stored in git-annex branch"
+	paramNothing (seek <$$> optParser)
+
+data Action
+	= SetConfig ConfigName ConfigValue
+	| GetConfig ConfigName
+	| UnsetConfig ConfigName
+
+type Name = String
+type Value = String
+
+optParser :: CmdParamsDesc -> Parser Action
+optParser _ = setconfig <|> getconfig <|> unsetconfig
+  where
+	setconfig = SetConfig
+		<$> strOption
+			( long "set"
+			<> help "set configuration"
+			<> metavar paramName
+			)
+		<*> strArgument
+			( metavar paramValue
+			)
+	getconfig = GetConfig <$> strOption
+		( long "get"
+		<> help "get configuration"
+		<> metavar paramName
+		)
+	unsetconfig = UnsetConfig <$> strOption
+		( long "unset"
+		<> help "unset configuration"
+		<> metavar paramName
+		)
+
+seek :: Action -> CommandSeek
+seek (SetConfig name val) = commandAction $ do
+	showStart name val
+	next $ next $ do
+		setGlobalConfig name val
+		return True
+seek (UnsetConfig name) = commandAction $ do
+	showStart name "unset"
+	next $ next $ do
+		unsetGlobalConfig name
+		return True
+seek (GetConfig name) = commandAction $ do
+	mv <- getGlobalConfig name
+	case mv of
+		Nothing -> stop
+		Just v -> do
+			liftIO $ putStrLn v
+			stop