sameas RemoteConfig inheritance

I found a way to avoid inheritance complicating anything outside of
Logs.Remote. It seems fine to require all inherited values to be
inherited and not set in the sameas remote's config. Since inherited
values will be used for stuff like encryption and perhaps chunking, which
control the actual content stored on the remote, it seems likely that
there will not be any reason to need them to vary between two remotes
that access the same underlying data store.

The newer version of containers is free; the minimum ghc version is
bundled with a newer version than that.

Logs/Remote.hs

@@ -1,6 +1,6 @@
 {- git-annex remote log
  - 
- - Copyright 2011 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2019 Joey Hess <id@joeyh.name>
  - 
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -22,6 +22,7 @@ import qualified Annex.Branch
 import Types.Remote
 import Logs
 import Logs.UUIDBased
+import Annex.SpecialRemote.Config
 
 import qualified Data.Map as M
 import Data.Char
@@ -34,14 +35,37 @@ configSet u cfg = do
 	c <- liftIO currentVectorClock
 	Annex.Branch.change remoteLog $
 		buildLogOld (byteString . encodeBS . showConfig)
-			. changeLog c u cfg
+			. changeLog c u (removeSameasInherited cfg)
 			. parseLogOld remoteConfigParser
 
 {- Map of remotes by uuid containing key/value config maps. -}
 readRemoteLog :: Annex (M.Map UUID RemoteConfig)
-readRemoteLog = simpleMap . parseLogOld remoteConfigParser
+readRemoteLog = addSameasInherited 
+	. simpleMap
+	. parseLogOld remoteConfigParser
 	<$> Annex.Branch.get remoteLog
 
+{- Each RemoteConfig that has a sameas-uuid inherits some fields
+ - from it. Such fields can only be set by inheritance; the RemoteConfig
+ - cannot provide values from them. -}
+addSameasInherited :: M.Map UUID RemoteConfig -> M.Map UUID RemoteConfig
+addSameasInherited m = M.map go m
+  where
+	go c = case toUUID <$> M.lookup sameasUUIDField c of
+		Nothing -> c
+		Just sameasuuid -> case M.lookup sameasuuid m of
+			Nothing -> c
+			Just parentc -> 
+				M.withoutKeys c sameasInherits			
+					`M.union`
+				M.restrictKeys parentc sameasInherits
+
+{- Remove any fields inherited from a sameas-uuid. -}
+removeSameasInherited :: RemoteConfig -> RemoteConfig
+removeSameasInherited c = case M.lookup sameasUUIDField c of
+	Nothing -> c
+	Just _ -> M.restrictKeys c sameasInherits
+
 remoteConfigParser :: A.Parser RemoteConfig
 remoteConfigParser = keyValToConfig . words . decodeBS <$> A.takeByteString