Org writer: support starting number cookies

This complements #7806 by supporting writing Org ordered lists that
start at a specific number.

src/Text/Pandoc/Writers/Org.hs

@@ -205,16 +205,19 @@ blockToOrg (OrderedList (start, _, delim) items) = do
   let delim' = case delim of
                     TwoParens -> OneParen
                     x         -> x
-  let markers = take (length items) $ orderedListMarkers
+  let markers = changeFst (counterCookie start) $
+                take (length items) $ orderedListMarkers
                                       (start, Decimal, delim')
-  let maxMarkerLength = maybe 0 maximum . nonEmpty $ map T.length markers
-  let markers' = map (\m -> let s = maxMarkerLength - T.length m
-                            in  m <> T.replicate s " ") markers
-  contents <- zipWithM orderedListItemToOrg markers' items
+  contents <- zipWithM orderedListItemToOrg markers items
   -- ensure that sublists have preceding blank line
   return $ blankline $$
            (if isTightList items then vcat else vsep) contents $$
            blankline
+  where
+    changeFst f (x:xs) = (f x) : xs
+    changeFst _ [] = []
+    counterCookie 1 marker = marker
+    counterCookie n marker = marker <> " [@" <> tshow n <> "]"
 blockToOrg (DefinitionList items) = do
   contents <- mapM definitionListItemToOrg items
   return $ vcat contents $$ blankline

test/Tests/Writers/Org.hs

@@ -50,6 +50,14 @@ tests =
           [ "1. [ ] a"
           , "2. [X] b"
           ]
+    , "ordered task list with starting number"
+      =: orderedListWith
+         (9, DefaultStyle, DefaultDelim)
+         [plain ("☐" <> space <> "a"), plain "☒ b"]
+      =?> T.unlines
+          [ "9. [@9] [ ] a"
+          , "10. [X] b"
+          ]
     , test (orgWithOpts def) "bullet without task_lists" $
       bulletList [plain "☐ a", plain "☒ b"]
       =?> T.unlines