Docx writer: better handle list items whose contents are lists (#6522)

If the first element of a bulleted or ordered list is another list,
then that first item will disappear if the target format is docx. This
changes the docx writer so that it prepends an empty string for those
cases. With this, no items will disappear.

Closes #5948.

src/Text/Pandoc/Writers/Docx.hs

@@ -3,6 +3,7 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE ViewPatterns        #-}
 {-# LANGUAGE FlexibleContexts    #-}
+{-# LANGUAGE LambdaCase          #-}
 {-# LANGUAGE OverloadedStrings   #-}
 {- |
    Module      : Text.Pandoc.Writers.Docx
@@ -1087,11 +1088,20 @@ listItemToOpenXML _ _ []                   = return []
 listItemToOpenXML opts numid (first:rest) = do
   oldInList <- gets stInList
   modify $ \st -> st{ stInList = True }
-  first' <- withNumId numid $ blockToOpenXML opts first
+  let isListBlock = \case
+        BulletList{}  -> True
+        OrderedList{} -> True
+        _             -> False
+  -- Prepend an empty string if the first entry is another
+  -- list. Otherwise the outer bullet will disappear.
+  let (first', rest') = if isListBlock first
+                           then (Plain [Str ""] , first:rest)
+                           else (first, rest)
+  first'' <- withNumId numid $ blockToOpenXML opts first'
   -- baseListId is the code for no list marker:
-  rest'  <- withNumId baseListId $ blocksToOpenXML opts rest
+  rest''  <- withNumId baseListId $ blocksToOpenXML opts rest'
   modify $ \st -> st{ stInList = oldInList }
-  return $ first' ++ rest'
+  return $ first'' ++ rest''
 
 alignmentToString :: Alignment -> [Char]
 alignmentToString alignment = case alignment of

test/Tests/Writers/Docx.hs

@@ -83,6 +83,11 @@ tests = [ testGroup "inlines"
             def
             "docx/lists_restarting.native"
             "docx/golden/lists_restarting.docx"
+          , docxTest
+            "lists with multiple initial list levels"
+            def
+            "docx/lists_multiple_initial.native"
+            "docx/golden/lists_multiple_initial.docx"
           , docxTest
             "definition lists"
             def

test/docx/lists_multiple_initial.native

@@ -0,0 +1,8 @@
+[OrderedList (1,Decimal,Period)
+ [[OrderedList (1,LowerAlpha,TwoParens)
+   [[Para [Str "foo"]]
+   ,[Para [Str "bar"]]]]]
+,BulletList
+ [[BulletList
+   [[Para [Str "foo"]]
+   ,[Para [Str "bar"]]]]]]