Fixed pipe tables -- headerless tables are not allowed.

GFM and PHP Markdown Extra pipe tables require headers.
Previously pandoc allowed pipe tables not to include headers,
and produced headerless pipe tables in Markdown output, but this
was based on a misconception about pipe table syntax. This
commit fixes this.

Note:  If you have been using headerless pipe tables, this may
cause existing tables to break.

Closes #1996.

2 files changed, 9 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 910936b34..fcd18fdc0 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1287,11 +1287,9 @@ pipeBreak = try $ do
 
 pipeTable :: MarkdownParser ([Alignment], [Double], F [Blocks], F [[Blocks]])
 pipeTable = try $ do
-  (heads,aligns) <- try ( pipeBreak >>= \als ->
-                     return (return $ replicate (length als) mempty, als))
-                  <|> ( pipeTableRow >>= \row -> pipeBreak >>= \als ->
-
-                          return (row, als) )
+  (heads,aligns) <- pipeTableRow >>= \row ->
+                    pipeBreak >>= \als ->
+                    return (row, als)
   lines' <- sequence <$> many1 pipeTableRow
   let widths = replicate (length aligns) 0.0
   return $ (aligns, widths, heads, lines')
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index 662373209..4ffdb2b36 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -508,7 +508,12 @@ pipeTable headless aligns rawHeaders rawRows = do
                              AlignCenter  -> ':':replicate w '-' ++ ":"
                              AlignRight   -> replicate (w + 1) '-' ++ ":"
                              AlignDefault -> replicate (w + 2) '-'
-  let header = if headless then empty else torow rawHeaders
+  -- note:  pipe tables can't completely lack a
+  -- header; for a headerless table, we need a header of empty cells.
+  -- see jgm/pandoc#1996.
+  let header = if headless
+                  then torow (replicate (length aligns) empty)
+                  else torow rawHeaders
   let border = nowrap $ text "|" <> hcat (intersperse (text "|") $
                         map toborder $ zip aligns widths) <> text "|"
   let body   = vcat $ map torow rawRows