Markdown reader/writer: spacing adjustments in tables.

* Markdown writer now includes a blank line at the end
  of the row in a single-row multiline table, to prevent it from being
  interpreted as a simple table.  Closes #4578.
* Markdown reader does a better job computing the relative width of
  the last column in a multiline table, so we can round-trip tables
  without constantly shrinking the last column.

2 files changed, 12 insertions, 4 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 0d1a83bab..156b2b622 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1341,11 +1341,16 @@ multilineTableHeader headless = try $ do
   newline
   let (lengths, lines') = unzip dashes
   let indices  = scanl (+) (length initSp) lines'
+  -- compensate for the fact that intercolumn spaces are
+  -- not included in the last index:
+  let indices' = case reverse indices of
+                      []     -> []
+                      (x:xs) -> reverse (x+1:xs)
   rawHeadsList <- if headless
                      then fmap (map (:[]) . tail .
-                              splitStringByIndices (init indices)) $ lookAhead anyLine
+                              splitStringByIndices (init indices')) $ lookAhead anyLine
                      else return $ transpose $ map
-                           (tail . splitStringByIndices (init indices))
+                           (tail . splitStringByIndices (init indices'))
                            rawContent
   let aligns   = zipWith alignType rawHeadsList lengths
   let rawHeads = if headless
@@ -1353,7 +1358,7 @@ multilineTableHeader headless = try $ do
                     else map (unlines . map trim) rawHeadsList
   heads <- fmap sequence $
             mapM ((parseFromString' (mconcat <$> many plain)).trim) rawHeads
-  return (heads, aligns, indices)
+  return (heads, aligns, indices')
 
 -- Parse a grid table:  starts with row of '-' on top, then header
 -- (which may be grid), then the rows,
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index 3bfa8a012..075858e5e 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -732,7 +732,10 @@ pandocTable opts multiline headless aligns widths rawHeaders rawRows = do
                   then empty
                   else border <> cr <> head'
   let body = if multiline
-                then vsep rows'
+                then vsep rows' $$
+                     if length rows' < 2
+                        then blankline -- #4578
+                        else empty
                 else vcat rows'
   let bottom = if headless
                   then underline