git-annex-config --set/--unset: No longer change the local git config setting

e53070c1f quietly made it set the local git config too, but that was never
documented anywhere, and it had surprising results. If I set
annex.largefiles globally in a repo, I would expect to be able to change it
in another repo, and the original repo would get the change and use it,
rather than being stuck on the old value set there.

And, if I have a local annex.largefiles and set a different global default,
I'd be surprised to have my local setting overwritten.

annex.securehashesonly does need to be set locally, since it's a security
feature and the global is only a default until it gets set locally. So
special cased.

CHANGELOG

@@ -11,6 +11,8 @@ git-annex (7.20191219) UNRELEASED; urgency=medium
     to more easily set a default that will also be used by clones,
     without needing to shoehorn the expression into the gitattributes file.
     The git config and gitattributes override that.
+  * git-annex-config --set/--unset: No longer change the local git config
+    setting, except for in the special case of annex.securehashesonly.
 
  -- Joey Hess <id@joeyh.name>  Wed, 18 Dec 2019 15:12:40 -0400
 

Command/Config.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
+{-# LANGUAGE OverloadedStrings #-}
+
 module Command.Config where
 
 import Command
@@ -54,12 +56,14 @@ seek :: Action -> CommandSeek
 seek (SetConfig ck@(ConfigKey name) val) = commandAction $
 	startingUsualMessages (decodeBS' name) (ActionItemOther (Just (fromConfigValue val))) $ do
 		setGlobalConfig ck val
-		setConfig ck (fromConfigValue val)
+		when (needLocalUpdate ck) $
+			setConfig ck (fromConfigValue val)
 		next $ return True
 seek (UnsetConfig ck@(ConfigKey name)) = commandAction $
 	startingUsualMessages (decodeBS' name) (ActionItemOther (Just "unset")) $do
 		unsetGlobalConfig ck
-		unsetConfig ck
+		when (needLocalUpdate ck) $
+			unsetConfig ck
 		next $ return True
 seek (GetConfig ck) = commandAction $
 	startingCustomOutput (ActionItemOther Nothing) $ do
@@ -67,3 +71,7 @@ seek (GetConfig ck) = commandAction $
 			Nothing -> return ()
 			Just (ConfigValue v) -> liftIO $ S8.putStrLn v
 		next $ return True
+
+needLocalUpdate :: ConfigKey -> Bool
+needLocalUpdate (ConfigKey "annex.securehashesonly") = True
+needLocalUpdate _ = False