sync --content: Fix dropping unwanted content from the local repository

This fixes a bug with the numcopies counting when using sync --content.
It did not always pass the local repo uuid to handleDropsFrom, and so the
numcopies counting was off by one, and unwanted local content would only be
dropped when there were numcopies+1 remote copies.

Also, support dropping local content that has reached an
exporttree remote that is not untrusted (currently only S3 remotes
with versioning).

Annex/Drop.hs

@@ -11,11 +11,12 @@ import Annex.Common
 import qualified Annex
 import Logs.Trust
 import Annex.NumCopies
-import Types.Remote (uuid, appendonly)
+import Types.Remote (uuid, appendonly, config)
 import qualified Remote
 import qualified Command.Drop
 import Command
 import Annex.Wanted
+import Annex.Export
 import Config
 import Annex.Content.Direct
 import qualified Database.Keys
@@ -30,7 +31,8 @@ type Reason = String
  - and numcopies settings.
  -
  - Skips trying to drop from remotes that are appendonly, since those drops
- - would presumably fail.
+ - would presumably fail. Also skips dropping from exporttree remotes,
+ - which don't allow dropping individual keys.
  -
  - The UUIDs are ones where the content is believed to be present.
  - The Remote list can include other remotes that do not have the content;
@@ -61,10 +63,9 @@ handleDropsFrom locs rs reason fromhere key afile preverified runner = do
 		AssociatedFile (Just f) -> nub (f : l)
 		AssociatedFile Nothing -> l
 	n <- getcopies fs
-	let rs' = filter (not . appendonly) rs
 	void $ if fromhere && checkcopies n Nothing
-		then go fs rs' n >>= dropl fs
-		else go fs rs' n
+		then go fs rs n >>= dropl fs
+		else go fs rs n
   where
 	getcopies fs = do
 		(untrusted, have) <- trustPartition UnTrusted locs
@@ -91,6 +92,8 @@ handleDropsFrom locs rs reason fromhere key afile preverified runner = do
 	go _ [] n = pure n
 	go fs (r:rest) n
 		| uuid r `S.notMember` slocs = go fs rest n
+		| appendonly r = go fs rest n
+		| exportTree (config r) = go fs rest n
 		| checkcopies n (Just $ Remote.uuid r) =
 			dropr fs r n >>= go fs rest
 		| otherwise = pure n