export appendonly support

Make `git annex export` check appendonly when removing a file from an
export, and not update the location log, since the remote still contains
the content.

This commit was supported by the NSF-funded DataLad project.

Command/Export.hs

@@ -285,11 +285,15 @@ cleanupUnexport r ea db eks loc = do
 			removeExportedLocation db (asKey ek) loc
 		flushDbQueue db
 
-	remaininglocs <- liftIO $ 
-		concat <$> forM eks (\ek -> getExportedLocation db (asKey ek))
-	when (null remaininglocs) $
-		forM_ eks $ \ek ->
-			logChange (asKey ek) (uuid r) InfoMissing
+	-- A readonly remote can support removeExportLocation to remove
+	-- the file from the exported tree, but still retain the content
+	-- and allow retrieving it.
+	unless (Remote.readonly) $ do
+		remaininglocs <- liftIO $ 
+			concat <$> forM eks (\ek -> getExportedLocation db (asKey ek))
+		when (null remaininglocs) $
+			forM_ eks $ \ek ->
+				logChange (asKey ek) (uuid r) InfoMissing
 	
 	removeEmptyDirectories ea db loc (map asKey eks)
 

Remote/Bup.hs

@@ -79,7 +79,7 @@ gen r u c gc = do
 		, remotetype = remote
 		, availability = if bupLocal buprepo then LocallyAvailable else GloballyAvailable
 		, readonly = False
-		, appendonly = True
+		, appendonly = False
 		, mkUnavailable = return Nothing
 		, getInfo = return [("repo", buprepo)]
 		, claimUrl = Nothing

Types/Remote.hs

@@ -123,7 +123,9 @@ data RemoteA a = Remote
 	-- a Remote can be known to be readonly
 	, readonly :: Bool
 	-- a Remote can allow writes but not have a way to delete content
-	-- from it
+	-- from it. Note that an export remote that supports removeExport
+	-- to remove a file from the exported tree, but still retains the
+	-- content in accessible form should set this to True.
 	, appendonly :: Bool
 	-- a Remote can be globally available. (Ie, "in the cloud".)
 	, availability :: Availability

doc/todo/versioning_in_export_remotes.mdwn

@@ -31,7 +31,7 @@ won't be updated, as discussed above.
 ## final plan
 
 Add an "appendOnly" field to Remote, indicating it retains all content stored
-in it.
+in it. done
 
 Let S3 remotes be configured with versioned=yes or something like that
 (what does S3 call the feature?) which enables appendOnly.
@@ -43,7 +43,7 @@ Make S3 refuse to removeKey when configured appendOnly, failing with an error.
 
 Make `git annex export` check appendOnly when removing a file from an
 export, and not update the location log, since the remote still contains
-the content.
+the content. done
 
 Make git-annex sync and the assistant skip trying to drop from appendOnly
 remotes since it's just going to fail.
@@ -52,8 +52,6 @@ Make exporttree=yes remotes that are appendOnly be trusted, and not force
 verification of content, since the usual concerns about losing data when an
 export is updated by someone else don't apply.
 
-Make bup an appendOnly remote.
-
 When a file was deleted from an exported tree, and then put back
 in a later exported tree, it might get re-uploaded even though the content
 is still retained in the versioned remote. S3 might have a way to avoid