Docx writer: ensure that documents don't start with a section separator

Any leading section separator is removed from the result.

Closes: #10578

src/Text/Pandoc/Writers/Docx.hs

@@ -6,7 +6,7 @@
 {-# LANGUAGE OverloadedStrings   #-}
 {- |
    Module      : Text.Pandoc.Writers.Docx
-   Copyright   : Copyright (C) 2012-2024 John MacFarlane
+   Copyright   : Copyright (C) 2012-2025 John MacFarlane
    License     : GNU GPL, version 2 or above
 
    Maintainer  : John MacFarlane <jgm@berkeley.edu>

src/Text/Pandoc/Writers/Docx/OpenXML.hs

@@ -9,7 +9,7 @@
 {-# LANGUAGE TypeApplications    #-}
 {- |
    Module      : Text.Pandoc.Writers.Docx
-   Copyright   : Copyright (C) 2012-2024 John MacFarlane
+   Copyright   : Copyright (C) 2012-2025 John MacFarlane
    License     : GNU GPL, version 2 or above
 
    Maintainer  : John MacFarlane <jgm@berkeley.edu>
@@ -20,7 +20,7 @@ Conversion of 'Pandoc' documents to docx.
 -}
 module Text.Pandoc.Writers.Docx.OpenXML ( writeOpenXML, maxListLevel ) where
 
-import Control.Monad (when, unless)
+import Control.Monad ((>=>), when, unless)
 import Control.Applicative ((<|>))
 import Control.Monad.Except (catchError)
 import Crypto.Hash (hashWith, SHA1(SHA1))
@@ -220,6 +220,15 @@ makeLOT opts = do
       ]) -- w:sdtContent
     ]] -- w:sdt
 
+-- | Separator element between sections
+sectionSeparator :: PandocMonad m => WS m (Maybe Content)
+sectionSeparator = do
+  asks envSectPr >>= \case
+    Just sectPrElem -> pure $
+      Just $ Elem (mknode "w:p" [] (mknode "w:pPr" [] [sectPrElem]))
+    Nothing -> pure
+      Nothing
+
 -- | Convert Pandoc document to rendered document contents plus two lists of
 -- OpenXML elements (footnotes and comments).
 writeOpenXML :: PandocMonad m
@@ -317,7 +326,17 @@ writeOpenXML opts (Pandoc meta blocks) = do
 
 -- | Convert a list of Pandoc blocks to OpenXML.
 blocksToOpenXML :: (PandocMonad m) => WriterOptions -> [Block] -> WS m [Content]
-blocksToOpenXML opts = fmap concat . mapM (blockToOpenXML opts) . separateTables . filter (not . isForeignRawBlock)
+blocksToOpenXML opts =
+  fmap concat . mapM (blockToOpenXML opts)
+  . separateTables . filter (not . isForeignRawBlock)
+  >=>
+  \case
+    a@(x:xs) -> do
+      sep <- sectionSeparator
+      if Just x == sep
+        then pure xs
+        else pure a
+    [] -> pure []
 
 isForeignRawBlock :: Block -> Bool
 isForeignRawBlock (RawBlock format _) = format /= "openxml"
@@ -395,13 +414,9 @@ blockToOpenXML' opts (Header lev (ident,_,kvs) lst) = do
                 Nothing -> return []
            else return []
   contents <- (number ++) <$> inlinesToOpenXML opts lst
-  sectpr <- asks envSectPr
-  let addSectionBreak
-       | isSection
-       , Just sectPrElem <- sectpr
-        = (Elem (mknode "w:p" []
-                   (mknode "w:pPr" [] [sectPrElem])) :)
-       | otherwise = id
+  addSectionBreak <- sectionSeparator >>= \case
+    Just sep | isSection -> pure (sep:)
+    _  -> pure id
   addSectionBreak <$>
     if T.null ident
        then return [Elem $ mknode "w:p" [] (map Elem paraProps ++ contents)]