Use the new builders, modify readers to preserve empty headers

The Builder.simpleTable now only adds a row to the TableHead when the
given header row is not null. This uncovered an inconsistency in the
readers: some would unconditionally emit a header filled with empty
cells, even if the header was not present. Now every reader has the
conditional behaviour. Only the XWiki writer depended on the header
row being always present; it now pads its head as necessary.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/Text/Pandoc/Writers/FB2.hs b/src/Text/Pandoc/Writers/FB2.hs
index 83bcf2038..5e6f1861e 100644
--- a/src/Text/Pandoc/Writers/FB2.hs
+++ b/src/Text/Pandoc/Writers/FB2.hs
@@ -336,10 +336,10 @@ blockToXml h@Header{} = do
 blockToXml HorizontalRule = return [ el "empty-line" () ]
 blockToXml (Table _ blkCapt specs thead tbody tfoot) = do
     let (caption, aligns, _, headers, rows) = toLegacyTable blkCapt specs thead tbody tfoot
-    hd <- mkrow "th" headers aligns
+    hd <- if null headers then pure [] else (:[]) <$> mkrow "th" headers aligns
     bd <- mapM (\r -> mkrow "td" r aligns) rows
     c <- el "emphasis" <$> cMapM toXml caption
-    return [el "table" (hd : bd), el "p" c]
+    return [el "table" (hd <> bd), el "p" c]
     where
       mkrow :: PandocMonad m => String -> [[Block]] -> [Alignment] -> FBM m Content
       mkrow tag cells aligns' =