auto-init autoenable=yes

Try to enable special remotes configured with autoenable=yes when git-annex
auto-initialization happens in a new clone of an existing repo. Previously,
git-annex init had to be explicitly run to enable them. That was a bit of a
wart of a special case for users to need to keep in mind.

Special remotes cannot display anything when autoenabled this way, to avoid
interfering with the output of git-annex query commands.

Any error messages will be hidden, and if it fails, nothing is displayed.
The user will realize the remote isn't enable when they try to use it,
and can run git-annex init manually then to try the autoenable again and
see what failed.

That seems like a reasonable approach, and it's less complicated than
communicating something across a pipe in order to display it as a side
message. Other reason not to do that is that, if the first command the
user runs is one like git-annex find that has machine readable output,
any message about autoenable failing would need to not be displayed anyway.
So better to not display a failure message ever, for consistency.

(Had to split out Remote.List.Util to avoid an import cycle.)

Command/Init.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -24,6 +24,7 @@ cmd = dontCheck repoExists $
 data InitOptions = InitOptions
 	{ initDesc :: String
 	, initVersion :: Maybe RepoVersion
+	, autoEnableOnly :: Bool
 	}
 
 optParser :: CmdParamsDesc -> Parser InitOptions
@@ -33,6 +34,10 @@ optParser desc = InitOptions
 		( long "version" <> metavar paramValue
 		<> help "Override default annex.version"
 		))
+	<*> switch
+		( long "autoenable"
+		<> help "only enable special remotes configured with autoenable=true"
+		)
 
 parseRepoVersion :: MonadFail m => String -> m RepoVersion
 parseRepoVersion s = case RepoVersion <$> readish s of
@@ -47,8 +52,11 @@ seek :: InitOptions -> CommandSeek
 seek = commandAction . start
 
 start :: InitOptions -> CommandStart
-start os = starting "init" (ActionItemOther (Just $ initDesc os)) $
-	perform os
+start os
+	| autoEnableOnly os = starting "init" (ActionItemOther (Just "autoenable")) $
+		performAutoEnableOnly
+	| otherwise = starting "init" (ActionItemOther (Just $ initDesc os)) $
+		perform os
 
 perform :: InitOptions -> CommandPerform
 perform os = do
@@ -63,3 +71,8 @@ perform os = do
 		(initVersion os)
 	Annex.SpecialRemote.autoEnable
 	next $ return True
+
+performAutoEnableOnly :: CommandPerform
+performAutoEnableOnly = do
+	Annex.SpecialRemote.autoEnable
+	next $ return True