avoid exporting non-annexed symlinks

So that importing does not replace them with plain files.

This works similarly to how the previous handling of submodules and
matchers did, except that annexed symlinks still get exported as plain
files of course, it's only non-annexed symlinks that it does not make sense
to export.

When symlinks have previously been exported, updating the export will
unexport them after upgrading to this commit.

Sponsored-by: Kevin Mueller on Patreon

Command/Export.hs

@@ -479,7 +479,8 @@ removeEmptyDirectories r db loc ks
 newtype ExportFiltered t = ExportFiltered t
 
 -- | Filters the tree to annexed files that are preferred content of the
--- remote, and also including non-annexed files, but not submodules.
+-- remote, and also including non-annexed files, but not submodules or
+-- non-annexed symlinks.
 --
 -- A log is written with tree items that were filtered out, so they can
 -- be added back in when importing from the remote.
@@ -505,17 +506,28 @@ filterExport r tree = logExportExcluded (uuid r) $ \logwriter -> do
 		case toTreeItemType mode of
 			-- Don't export submodule entries.
 			Just TreeSubmodule -> excluded
-			_ -> case mmatcher of
-				Nothing -> return (Just ti)
-				Just matcher -> catKey sha >>= \case
-					Just k -> checkmatcher matcher k
-					-- Always export non-annexed files.
-					Nothing -> return (Just ti)
+			Just TreeSymlink -> checkkey True
+			_ -> checkkey False
 	  where
 		excluded = do
 			() <- liftIO $ logwriter ti
 			return Nothing
 
+		checkkey issymlink =
+			case mmatcher of
+				Nothing
+					| issymlink -> catKey sha >>= \case
+						Just _ -> return (Just ti)
+						Nothing
+							| issymlink -> excluded
+							| otherwise -> return (Just ti)
+					| otherwise -> return (Just ti)
+				Just matcher -> catKey sha >>= \case
+					Just k -> checkmatcher matcher k
+					Nothing
+						| issymlink -> excluded
+						| otherwise -> return (Just ti)
+
 		checkmatcher matcher k = do
 			let mi = MatchingInfo $ ProvidedInfo
 				{ providedFilePath = Just $