don't support removing content from export with removeKey

There does not seem to be a use case for supporting that, and it would
need a lot of complication to support it in a way that allows eventual
consistency when two repositories are updating the same export.

This commit was sponsored by Henrik Riomar on Patreon.

2 files changed, 9 insertions, 46 deletions

diff --git a/Remote/Helper/Export.hs b/Remote/Helper/Export.hs
index edd0b96df..df75dacd0 100644
--- a/Remote/Helper/Export.hs
+++ b/Remote/Helper/Export.hs
@@ -117,20 +117,15 @@ adjustExportable r = case M.lookup "exporttree" (config r) of
 						warning $ "exported content cannot be verified due to using the " ++ formatKeyVariety (keyVariety k) ++ " backend"
 						return False
 			, retrieveKeyFileCheap = \_ _ _ -> return False
-			-- Remove all files a key was exported to.
-			, removeKey = \k -> do
-				locs <- liftIO $ getExportLocation db k
-				ea <- exportActions r
-				oks <- forM locs $ \loc ->
-					ifM (removeExport ea k loc)
-						( do
-							liftIO $ do
-								removeExportLocation db k loc
-								flushDbQueue db
-							removeEmptyDirectories ea db loc [k]
-						, return False
-						)
-				return (and oks)
+			-- Removing a key from an export would need to
+			-- change the tree in the export log to not include
+			-- the file. Otherwise, conflicts when removing
+			-- files would not be dealt with correctly.
+			-- There does not seem to be a good use case for
+			-- removing a key from an export in any case.
+			, removeKey = \_k -> do
+				warning "dropping content from an export is not supported; use `git annex export` to export a tree that lacks the files you want to remove"
+				return False
 			-- Can't lock content on exports, since they're
 			-- not key/value stores, and someone else could
 			-- change what's exported to a file at any time.
diff --git a/doc/todo/export.mdwn b/doc/todo/export.mdwn
index 0ed04d7e7..c6d79f7a7 100644
--- a/doc/todo/export.mdwn
+++ b/doc/todo/export.mdwn
@@ -38,38 +38,6 @@ Work is in progress. Todo list:
   Updating the export db could diff the last exported treeish with the
   logged treeish. Add/delete exported files from the database to get
   it to the same state as the remote database.
-  But, removeKey from an export makes the diff approach problimatic;
-  see below.
-
-* removeKey from an export is problimatic in distributed context
-
-  A file can be removed from an export via removeKey,
-  which updates the export db and location log, but does not update
-  the export log. This is problimatic when multiple repos are updating
-  an export.
-
-  1. In repo A, file F with content K is exported
-  2. In repo B, file F with content K' is exported, since F changed in the
-     exported treeish.
-  3. In repo A, file F is removed from the export, which results in
-     K being removed from the location log for the export.
-
-  Did #3 happen before or after #2?  
-  If #3 occurred before #2, then K' is present in the export
-  and the location log is correct.  
-  If #3 occurred after #2, and A and B's git-annex branches
-  were not synced, then K' was accidentially removed
-  from the export, and the location log is now wrong.
-
-  Is there any reason to allow removeKey from an export?
-  Why would someone want to drop a single file from an export?
-  Why not remove the file from a tree, and export the new tree?
-
-  (Alternatively, removeKey could itself update the exported tree,
-  removing the file from it, and update the export log accordingly.
-  This would avoid the problem. But that's complication and it would be
-  rather slow and bloat the git repo with a lot of intermediate trees
-  when dropping multiple keys.)
 
 * git-annex sync to export and export tracking branch