compute remote: get input files from other remotes

This needed some refactoring to avoid cycles, since Remote.Compute
cannot import Remote.List. Instead, it uses Annex.remotes. Which must be
populated by something else, but we know it has been, because something
is using Remote.Compute, which it must have found in the remote list,
which populates that.

In Remote.Compute, keyPossibilities' is called with all loggedLocations,
without the trustExclude DeadTrusted that keyLocations does. There is
another cycle there. This may be a problem if a dead repository is still
a remote.

This is missing cycle prevention, and it's certianly possible to make 2
files in the compute remote co-depend on one-another. Hopefully not in a
real world situation, but it an attacker could certainly do it. Cycle
prevention will need to be added to this.

Remote/Compute.hs

@@ -32,14 +32,17 @@ import Config
 import Config.Cost
 import Remote.Helper.Special
 import Remote.Helper.ExportImport
+import Remote.List.Util
 import Annex.SpecialRemote.Config
 import Annex.UUID
 import Annex.Content
 import Annex.Tmp
 import Annex.GitShaKey
 import Annex.CatFile
+import qualified Annex.Transfer
 import Logs.MetaData
 import Logs.EquivilantKeys
+import Logs.Location
 import Utility.Metered
 import Utility.TimeStamp
 import Utility.Env
@@ -359,6 +362,8 @@ runComputeProgram
 	-> ComputeState
 	-> ImmutableState
 	-> (OsPath -> Annex (Key, Maybe (Either Git.Sha OsPath)))
+	-- ^ get input file's content, or Nothing when adding a computation
+	-- without actually performing it
 	-> (ComputeState -> OsPath -> NominalDiffTime -> Annex v)
 	-> Annex v
 runComputeProgram (ComputeProgram program) state (ImmutableState immutablestate) getinputcontent cont =
@@ -491,13 +496,34 @@ computeKey rs (ComputeProgram program) k _af dest p vc =
 	getinputcontent state f =
 		case M.lookup (fromOsPath f) (computeInputs state) of
 			Just inputkey -> case keyGitSha inputkey of
-				Nothing -> do
-					obj <- calcRepo (gitAnnexLocation inputkey)
-					-- XXX get input object when not present
-					return (inputkey, Just (Right obj))
+				Nothing -> 
+					let retkey = do
+						obj <- calcRepo (gitAnnexLocation inputkey)
+						return (inputkey, Just (Right obj))
+					in ifM (inAnnex inputkey)
+						( retkey
+						, do
+							getinputcontent' f inputkey
+							retkey
+						)
 				Just gitsha ->
 					return (inputkey, Just (Left gitsha))
 			Nothing -> error "internal"
+	
+	getinputcontent' f inputkey = do
+		remotelist <- Annex.getState Annex.remotes
+		locs <- loggedLocations inputkey
+		rs <- keyPossibilities' (IncludeIgnored False) inputkey locs remotelist
+		if null rs
+			then return ()
+			else void $ firstM (getinputcontentfrom f inputkey) rs
+	
+	-- TODO cycle prevention
+	getinputcontentfrom f inputkey r = do
+		showAction $ "getting input " <> QuotedPath f
+			<> " from " <> UnquotedString (name r)
+		Annex.Transfer.download r inputkey (AssociatedFile (Just f))
+			Annex.Transfer.stdRetry Annex.Transfer.noNotification
 
 	computeskey state = 
 		case M.keys $ M.filter (== Just k) (computeOutputs state) of