path: root/src/Text/Pandoc/Writers/Markdown.hs

{-# LANGUAGE MultiWayIf          #-}
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections       #-}
{-# LANGUAGE ViewPatterns        #-}
{- |
   Module      : Text.Pandoc.Writers.Markdown
   Copyright   : Copyright (C) 2006-2021 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley.edu>
   Stability   : alpha
   Portability : portable

Conversion of 'Pandoc' documents to markdown-formatted plain text.

Markdown:  <https://daringfireball.net/projects/markdown/>
-}
module Text.Pandoc.Writers.Markdown (
  writeMarkdown,
  writeCommonMark,
  writePlain) where
import Control.Monad.Reader
import Control.Monad.State.Strict
import Data.Default
import Data.List (intersperse, sortOn, transpose)
import Data.List.NonEmpty (nonEmpty, NonEmpty(..))
import qualified Data.Map as M
import Data.Maybe (fromMaybe, mapMaybe)
import qualified Data.Set as Set
import Data.Text (Text)
import qualified Data.Text as T
import Text.HTML.TagSoup (Tag (..), isTagText, parseTags)
import Text.Pandoc.Class.PandocMonad (PandocMonad, report)
import Text.Pandoc.Definition
import Text.Pandoc.Logging
import Text.Pandoc.Options
import Text.Pandoc.Parsing hiding (blankline, blanklines, char, space)
import Text.DocLayout
import Text.Pandoc.Shared
import Text.Pandoc.Writers.Shared
import Text.Pandoc.Templates (renderTemplate)
import Text.DocTemplates (Val(..), Context(..), FromContext(..))
import Text.Pandoc.Walk
import Text.Pandoc.Writers.HTML (writeHtml5String)
import Text.Pandoc.Writers.Markdown.Inline (inlineListToMarkdown)
import Text.Pandoc.Writers.Markdown.Types (MarkdownVariant(..),
                                           WriterState(..),
                                           WriterEnv(..),
                                           Ref, Refs, MD, evalMD)

-- | Convert Pandoc to Markdown.
writeMarkdown :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeMarkdown opts document =
  evalMD (pandocToMarkdown opts{
             writerWrapText = if isEnabled Ext_hard_line_breaks opts
                              then WrapNone
                              else writerWrapText opts }
             document) def def

-- | Convert Pandoc to plain text (like markdown, but without links,
-- pictures, or inline formatting).
writePlain :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writePlain opts document =
  evalMD (pandocToMarkdown opts document) def{ envVariant = PlainText } def

-- | Convert Pandoc to Commonmark.
writeCommonMark :: PandocMonad m => WriterOptions -> Pandoc -> m Text
writeCommonMark opts document =
  evalMD (pandocToMarkdown opts document) def{ envVariant = Commonmark } def

pandocTitleBlock :: Doc Text -> [Doc Text] -> Doc Text -> Doc Text
pandocTitleBlock tit auths dat =
  hang 2 (text "% ") tit <> cr <>
  hang 2 (text "% ") (vcat $ map nowrap auths) <> cr <>
  hang 2 (text "% ") dat <> cr

mmdTitleBlock :: Context Text -> Doc Text
mmdTitleBlock (Context hashmap) =
  vcat $ map go $ sortOn (T.toCaseFold . fst) $ M.toList hashmap
  where go (k,v) =
          case (text (T.unpack k), v) of
               (k', ListVal xs)
                 | null xs        -> empty
                 | otherwise      -> k' <> ":" <> space <>
                                      hcat (intersperse "; " $
                                            mapMaybe fromVal xs)
               (k', SimpleVal x)
                      | isEmpty x -> empty
                      | otherwise -> k' <> ":" <> space <>
                                     nest 2 (removeBlankLines (chomp x))
               _                  -> empty
        removeBlankLines BlankLines{} = cr <> text "." <> cr
        removeBlankLines (Concat x y) = removeBlankLines x <>
                                        removeBlankLines y
        removeBlankLines x            = x

plainTitleBlock :: Doc Text -> [Doc Text] -> Doc Text -> Doc Text
plainTitleBlock tit auths dat =
  tit <> cr <>
  hcat (intersperse (text "; ") auths) <> cr <>
  dat <> cr

yamlMetadataBlock :: Context Text -> Doc Text
yamlMetadataBlock v = "---" $$ contextToYaml v $$ "---"

contextToYaml :: Context Text -> Doc Text
contextToYaml (Context o) =
  vcat $ map keyvalToYaml $ sortOn (T.toCaseFold . fst) $ M.toList o
 where
  keyvalToYaml (k,v) =
          case (text (T.unpack k), v) of
               (k', ListVal vs)
                 | null vs        -> empty
                 | otherwise      -> (k' <> ":") $$ valToYaml v
               (k', MapVal (Context m))
                 | M.null m       -> k' <> ": {}"
                 | otherwise      -> (k' <> ":") $$ nest 2 (valToYaml v)
               (_, SimpleVal x)
                     | isEmpty x  -> empty
               (_, NullVal)       -> empty
               (k', _)            -> k' <> ":" <+> hang 2 "" (valToYaml v)

valToYaml :: Val Text -> Doc Text
valToYaml (ListVal xs) =
  vcat $ map (\v -> hang 2 "- " (valToYaml v)) xs
valToYaml (MapVal c) = contextToYaml c
valToYaml (BoolVal True) = "true"
valToYaml (BoolVal False) = "false"
valToYaml (SimpleVal x)
  | isEmpty x = empty
  | otherwise =
      if hasNewlines x
         then hang 0 ("|" <> cr) x
         else if fst $ foldr needsDoubleQuotes (False, True) x
           then "\"" <> fmap escapeInDoubleQuotes x <> "\""
           else x
    where
      needsDoubleQuotes t (positive, isFirst)
        = if T.any isBadAnywhere t ||
             (isFirst && T.any isYamlPunct (T.take 1 t))
              then (True, False)
              else (positive, False)
      isBadAnywhere '#' = True
      isBadAnywhere ':' = True
      isBadAnywhere '`' = False
      isBadAnywhere _   = False
      hasNewlines NewLine = True
      hasNewlines BlankLines{} = True
      hasNewlines CarriageReturn = True
      hasNewlines (Concat w z) = hasNewlines w || hasNewlines z
      hasNewlines _ = False
      isYamlPunct = (`elem` ['-','?',':',',','[',']','{','}',
                             '#','&','*','!','|','>','\'','"', '%','@','`'])
      escapeInDoubleQuotes = T.replace "\"" "\\\"" . T.replace "\\" "\\\\"
valToYaml _ = empty

-- | Return markdown representation of document.
pandocToMarkdown :: PandocMonad m => WriterOptions -> Pandoc -> MD m Text
pandocToMarkdown opts (Pandoc meta blocks) = do
  let colwidth = if writerWrapText opts == WrapAuto
                    then Just $ writerColumns opts
                    else Nothing
  variant <- asks envVariant
  metadata <- metaToContext'
               (blockListToMarkdown opts)
               (inlineListToMarkdown opts)
               meta
  let title' = fromMaybe empty $ getField "title" metadata
  let authors' = fromMaybe [] $ getField "author" metadata
  let date' = fromMaybe empty $ getField "date" metadata
  let titleblock = case writerTemplate opts of
                        Just _ | variant == PlainText ->
                                 plainTitleBlock title' authors' date'
                               | isEnabled Ext_yaml_metadata_block opts ->
                                   yamlMetadataBlock metadata
                               | isEnabled Ext_pandoc_title_block opts ->
                                   pandocTitleBlock title' authors' date'
                               | isEnabled Ext_mmd_title_block opts ->
                                   mmdTitleBlock metadata
                               | otherwise -> empty
                        Nothing -> empty
  toc <- if writerTableOfContents opts
         then blockToMarkdown opts ( toTableOfContents opts blocks )
         else return mempty
  -- Strip off final 'references' header if markdown citations enabled
  let blocks' = if isEnabled Ext_citations opts
                   then case reverse blocks of
                             (Div ("refs",_,_) _):xs -> reverse xs
                             _                       -> blocks
                   else blocks
  body <- blockListToMarkdown opts blocks'
  notesAndRefs' <- notesAndRefs opts
  let main = body <> notesAndRefs'
  let context  = -- for backwards compatibility we populate toc
                 -- with the contents of the toc, rather than a
                 -- boolean:
                 defField "toc" toc
               $ defField "table-of-contents" toc
               $ defField "body" main
               $ (if isNullMeta meta
                     then id
                     else defField "titleblock" titleblock)
               $ addVariablesToContext opts metadata
  return $ render colwidth $
    case writerTemplate opts of
       Nothing  -> main
       Just tpl -> renderTemplate tpl context

-- | Return markdown representation of reference key table.
refsToMarkdown :: PandocMonad m => WriterOptions -> Refs -> MD m (Doc Text)
refsToMarkdown opts refs = vcat <$> mapM (keyToMarkdown opts) refs

-- | Return markdown representation of a reference key.
keyToMarkdown :: PandocMonad m
              => WriterOptions
              -> Ref
              -> MD m (Doc Text)
keyToMarkdown opts (label', (src, tit), attr) = do
  let tit' = if T.null tit
                then empty
                else space <> "\"" <> literal tit <> "\""
  return $ nest 2 $ hang 2
            ("[" <> literal label' <> "]:" <> space) (literal src <> tit')
            <+> linkAttributes opts attr

-- | Return markdown representation of notes.
notesToMarkdown :: PandocMonad m => WriterOptions -> [[Block]] -> MD m (Doc Text)
notesToMarkdown opts notes = do
  n <- gets stNoteNum
  notes' <- zipWithM (noteToMarkdown opts) [n..] notes
  modify $ \st -> st { stNoteNum = stNoteNum st + length notes }
  return $ vsep notes'

-- | Return markdown representation of a note.
noteToMarkdown :: PandocMonad m => WriterOptions -> Int -> [Block] -> MD m (Doc Text)
noteToMarkdown opts num blocks = do
  contents  <- blockListToMarkdown opts blocks
  let num' = literal $ writerIdentifierPrefix opts <> tshow num
  let marker = if isEnabled Ext_footnotes opts
                  then literal "[^" <> num' <> literal "]:"
                  else literal "[" <> num' <> literal "]"
  let markerSize = 4 + offset num'
  let spacer = case writerTabStop opts - markerSize of
                     n | n > 0  -> literal $ T.replicate n " "
                     _ -> literal " "
  return $ if isEnabled Ext_footnotes opts
              then hang (writerTabStop opts) (marker <> spacer) contents
              else marker <> spacer <> contents

attrsToMarkdown :: Attr -> Doc Text
attrsToMarkdown attribs = braces $ hsep [attribId, attribClasses, attribKeys]
        where attribId = case attribs of
                                ("",_,_) -> empty
                                (i,_,_)  -> "#" <> escAttr i
              attribClasses = case attribs of
                                (_,[],_) -> empty
                                (_,cs,_) -> hsep $
                                            map (escAttr . ("."<>))
                                            cs
              attribKeys = case attribs of
                                (_,_,[]) -> empty
                                (_,_,ks) -> hsep $
                                            map (\(k,v) -> escAttr k
                                              <> "=\"" <>
                                              escAttr v <> "\"") ks
              escAttr          = mconcat . map escAttrChar . T.unpack
              escAttrChar '"'  = literal "\\\""
              escAttrChar '\\' = literal "\\\\"
              escAttrChar c    = literal $ T.singleton c

linkAttributes :: WriterOptions -> Attr -> Doc Text
linkAttributes opts attr =
  if isEnabled Ext_link_attributes opts && attr /= nullAttr
     then attrsToMarkdown attr
     else empty

-- | Ordered list start parser for use in Para below.
olMarker :: Parser Text ParserState ()
olMarker = do (start, style', delim) <- anyOrderedListMarker
              if delim == Period &&
                          (style' == UpperAlpha || (style' == UpperRoman &&
                          start `elem` [1, 5, 10, 50, 100, 500, 1000]))
                          then mzero -- it needs 2 spaces anyway
                          else eof

-- | True if string begins with an ordered list marker
beginsWithOrderedListMarker :: Text -> Bool
beginsWithOrderedListMarker str =
  case runParser olMarker defaultParserState "para start" (T.take 10 str) of
         Left  _ -> False
         Right _ -> True

notesAndRefs :: PandocMonad m => WriterOptions -> MD m (Doc Text)
notesAndRefs opts = do
  notes' <- gets stNotes >>= notesToMarkdown opts . reverse
  modify $ \s -> s { stNotes = [] }
  refs' <- gets stRefs >>= refsToMarkdown opts . reverse
  modify $ \s -> s { stPrevRefs = stPrevRefs s ++ stRefs s
                   , stRefs = []}

  let endSpacing =
        if | writerReferenceLocation opts == EndOfDocument -> empty
           | isEmpty notes' && isEmpty refs' -> empty
           | otherwise -> blankline

  return $
    (if isEmpty notes' then empty else blankline <> notes') <>
    (if isEmpty refs' then empty else blankline <> refs') <>
    endSpacing

-- | Convert Pandoc block element to markdown.
blockToMarkdown :: PandocMonad m
                => WriterOptions -- ^ Options
                -> Block         -- ^ Block element
                -> MD m (Doc Text)
blockToMarkdown opts blk =
  local (\env -> env {envBlockLevel = envBlockLevel env + 1}) $
  do doc <- blockToMarkdown' opts blk
     blkLevel <- asks envBlockLevel
     if writerReferenceLocation opts == EndOfBlock && blkLevel == 1
       then notesAndRefs opts >>= (\d -> return $ doc <> d)
       else return doc

blockToMarkdown' :: PandocMonad m
                 => WriterOptions -- ^ Options
                 -> Block         -- ^ Block element
                 -> MD m (Doc Text)
blockToMarkdown' _ Null = return empty
blockToMarkdown' opts (Div attrs ils) = do
  contents <- blockListToMarkdown opts ils
  variant <- asks envVariant
  return $
    case () of
         _ | isEnabled Ext_fenced_divs opts &&
             attrs /= nullAttr ->
                nowrap (literal ":::" <+> attrsToMarkdown attrs) $$
                chomp contents $$
                literal ":::" <> blankline
           | isEnabled Ext_native_divs opts ||
             (isEnabled Ext_raw_html opts &&
              (variant == Commonmark ||
               isEnabled Ext_markdown_in_html_blocks opts)) ->
                tagWithAttrs "div" attrs <> blankline <>
                contents <> blankline <> "</div>" <> blankline
           | isEnabled Ext_raw_html opts &&
             isEnabled Ext_markdown_attribute opts ->
                tagWithAttrs "div" attrs' <> blankline <>
                contents <> blankline <> "</div>" <> blankline
           | otherwise -> contents <> blankline
       where (id',classes',kvs') = attrs
             attrs' = (id',classes',("markdown","1"):kvs')
blockToMarkdown' opts (Plain inlines) = do
  -- escape if para starts with ordered list marker
  variant <- asks envVariant
  let escapeMarker = T.concatMap $ \x -> if x `elemText` ".()"
                                         then T.pack ['\\', x]
                                         else T.singleton x
  let startsWithSpace (Space:_)     = True
      startsWithSpace (SoftBreak:_) = True
      startsWithSpace _             = False
  let inlines' =
        if variant == PlainText
           then inlines
           else case inlines of
                  (Str t:ys)
                    | null ys || startsWithSpace ys
                    , beginsWithOrderedListMarker t
                    -> RawInline (Format "markdown") (escapeMarker t):ys
                  (Str t:_)
                    | t == "+" || t == "-" ||
                      (t == "%" && isEnabled Ext_pandoc_title_block opts &&
                                   isEnabled Ext_all_symbols_escapable opts)
                    -> RawInline (Format "markdown") "\\" : inlines
                  _ -> inlines
  contents <- inlineListToMarkdown opts inlines'
  return $ contents <> cr
-- title beginning with fig: indicates figure
blockToMarkdown' opts (Para [Image attr alt (src,tgt@(T.stripPrefix "fig:" -> Just tit))])
  | isEnabled Ext_raw_html opts &&
    not (isEnabled Ext_link_attributes opts) &&
    attr /= nullAttr = -- use raw HTML
    (<> blankline) . literal . T.strip <$>
      writeHtml5String opts{ writerTemplate = Nothing }
        (Pandoc nullMeta [Para [Image attr alt (src,tgt)]])
  | otherwise = blockToMarkdown opts (Para [Image attr alt (src,tit)])
blockToMarkdown' opts (Para inlines) =
  (<> blankline) `fmap` blockToMarkdown opts (Plain inlines)
blockToMarkdown' opts (LineBlock lns) =
  if isEnabled Ext_line_blocks opts
  then do
    mdLines <- mapM (inlineListToMarkdown opts) lns
    return $ vcat (map (hang 2 (literal "| ")) mdLines) <> blankline
  else blockToMarkdown opts $ linesToPara lns
blockToMarkdown' opts b@(RawBlock f str) = do
  variant <- asks envVariant
  let Format fmt = f
  let rawAttribBlock = return $
         (literal "```{=" <> literal fmt <> "}") $$
         literal str $$
         (literal "```" <> literal "\n")
  let renderEmpty = mempty <$ report (BlockNotRendered b)
  case variant of
    PlainText -> renderEmpty
    Commonmark
      | f `elem` ["gfm", "commonmark", "commonmark_x", "markdown"]
         -> return $ literal str <> literal "\n"
    Markdown
      | f `elem` ["markdown", "markdown_github", "markdown_phpextra",
                  "markdown_mmd", "markdown_strict"]
         -> return $ literal str <> literal "\n"
    _ | isEnabled Ext_raw_attribute opts -> rawAttribBlock
      | f `elem` ["html", "html5", "html4"]
      , isEnabled Ext_markdown_attribute opts
         -> return $ literal (addMarkdownAttribute str) <> literal "\n"
      | f `elem` ["html", "html5", "html4"]
      , isEnabled Ext_raw_html opts
         -> return $ literal str <> literal "\n"
      | f `elem` ["latex", "tex"]
      , isEnabled Ext_raw_tex opts
         -> return $ literal str <> literal "\n"
    _ -> renderEmpty
blockToMarkdown' opts HorizontalRule =
  return $ blankline <> literal (T.replicate (writerColumns opts) "-") <> blankline
blockToMarkdown' opts (Header level attr inlines) = do

  -- first, if we're putting references at the end of a section, we
  -- put them here.
  blkLevel <- asks envBlockLevel
  refs <- if writerReferenceLocation opts == EndOfSection && blkLevel == 1
          then notesAndRefs opts
          else return empty

  variant <- asks envVariant
  -- we calculate the id that would be used by auto_identifiers
  -- so we know whether to print an explicit identifier
  ids <- gets stIds
  let autoId = uniqueIdent (writerExtensions opts) inlines ids
  modify $ \st -> st{ stIds = Set.insert autoId ids }
  let attr' = case attr of
                   ("",[],[]) -> empty
                   (id',[],[]) | isEnabled Ext_auto_identifiers opts
                                 && id' == autoId -> empty
                   (id',_,_)   | isEnabled Ext_mmd_header_identifiers opts ->
                                    space <> brackets (literal id')
                   _ | isEnabled Ext_header_attributes opts ->
                                    space <> attrsToMarkdown attr
                     | otherwise -> empty
  contents <- inlineListToMarkdown opts $
                 -- ensure no newlines; see #3736
                 walk lineBreakToSpace $
                   if level == 1 && variant == PlainText &&
                      isEnabled Ext_gutenberg opts
                      then capitalize inlines
                      else inlines

  let setext = writerSetextHeaders opts
  when (not setext && isEnabled Ext_literate_haskell opts) $
    report $ ATXHeadingInLHS level (render Nothing contents)

  let hdr = nowrap $ case level of
            1 | variant == PlainText ->
                if isEnabled Ext_gutenberg opts
                   then blanklines 3 <> contents <> blanklines 2
                   else contents <> blankline
              | setext ->
                  contents <> attr' <> cr <> literal (T.replicate (offset contents) "=") <>
                  blankline
            2 | variant == PlainText ->
                if isEnabled Ext_gutenberg opts
                   then blanklines 2 <> contents <> blankline
                   else contents <> blankline
              | setext ->
                  contents <> attr' <> cr <> literal (T.replicate (offset contents) "-") <>
                  blankline
            -- ghc interprets '#' characters in column 1 as linenum specifiers.
            _ | variant == PlainText || isEnabled Ext_literate_haskell opts ->
                contents <> blankline
            _ -> literal (T.replicate level "#") <> space <> contents <> attr' <> blankline

  return $ refs <> hdr
blockToMarkdown' opts (CodeBlock (_,classes,_) str)
  | "haskell" `elem` classes && "literate" `elem` classes &&
    isEnabled Ext_literate_haskell opts =
  return $ prefixed "> " (literal str) <> blankline
blockToMarkdown' opts (CodeBlock attribs str) = do
  variant <- asks envVariant
  return $
   case attribs == nullAttr of
     False | variant == Commonmark ||
             isEnabled Ext_backtick_code_blocks opts ->
          backticks <> attrs <> cr <> literal str <> cr <> backticks <> blankline
           | isEnabled Ext_fenced_code_blocks opts ->
          tildes <> attrs <> cr <> literal str <> cr <> tildes <> blankline
     _ -> nest (writerTabStop opts) (literal str) <> blankline
   where
     endlineLen c = maybe 3 ((+1) . maximum) $ nonEmpty $
                        [T.length ln
                         | ln <- map trim (T.lines str)
                         , T.pack [c,c,c] `T.isPrefixOf` ln
                         , T.all (== c) ln]
     endline c = literal $ T.replicate (endlineLen c) $ T.singleton c
     backticks = endline '`'
     tildes = endline '~'
     attrs  = if isEnabled Ext_fenced_code_attributes opts
                 then nowrap $ " " <> attrsToMarkdown attribs
                 else case attribs of
                            (_,cls:_,_) -> " " <> literal cls
                            _             -> empty
blockToMarkdown' opts (BlockQuote blocks) = do
  variant <- asks envVariant
  -- if we're writing literate haskell, put a space before the bird tracks
  -- so they won't be interpreted as lhs...
  let leader
        | isEnabled Ext_literate_haskell opts = " > "
        | variant == PlainText = "  "
        | otherwise            = "> "
  contents <- blockListToMarkdown opts blocks
  return $ prefixed leader contents <> blankline
blockToMarkdown' opts t@(Table _ blkCapt specs thead tbody tfoot) = do
  let (caption, aligns, widths, headers, rows) = toLegacyTable blkCapt specs thead tbody tfoot
  let numcols = maximum (length aligns :| length widths :
                           map length (headers:rows))
  caption' <- inlineListToMarkdown opts caption
  let caption''
        | null caption = blankline
        | isEnabled Ext_table_captions opts
        = blankline $$ (": " <> caption') $$ blankline
        | otherwise = blankline $$ caption' $$ blankline
  let hasSimpleCells = onlySimpleTableCells $ headers : rows
  let isSimple = hasSimpleCells && all (==0) widths
  let isPlainBlock (Plain _) = True
      isPlainBlock _         = False
  let hasBlocks = not (all isPlainBlock $ concat . concat $ headers:rows)
  let padRow r = case numcols - length r of
                       x | x > 0 -> r ++ replicate x empty
                         | otherwise -> r
  let aligns' = case numcols - length aligns of
                     x | x > 0 -> aligns ++ replicate x AlignDefault
                       | otherwise -> aligns
  let widths' = case numcols - length widths of
                     x | x > 0 -> widths ++ replicate x 0.0
                       | otherwise -> widths
  (nst,tbl) <-
     case True of
          _ | isSimple &&
              isEnabled Ext_simple_tables opts -> do
                rawHeaders <- padRow <$> mapM (blockListToMarkdown opts) headers
                rawRows <- mapM (fmap padRow . mapM (blockListToMarkdown opts))
                           rows
                (nest 2,) <$> pandocTable opts False (all null headers)
                                aligns' widths' rawHeaders rawRows
            | isSimple &&
              isEnabled Ext_pipe_tables opts -> do
                rawHeaders <- padRow <$> mapM (blockListToMarkdown opts) headers
                rawRows <- mapM (fmap padRow . mapM (blockListToMarkdown opts))
                           rows
                (id,) <$> pipeTable (all null headers) aligns' rawHeaders rawRows
            | not hasBlocks &&
              isEnabled Ext_multiline_tables opts -> do
                rawHeaders <- padRow <$> mapM (blockListToMarkdown opts) headers
                rawRows <- mapM (fmap padRow . mapM (blockListToMarkdown opts))
                           rows
                (nest 2,) <$> pandocTable opts True (all null headers)
                                aligns' widths' rawHeaders rawRows
            | isEnabled Ext_grid_tables opts &&
               writerColumns opts >= 8 * numcols -> (id,) <$>
                gridTable opts blockListToMarkdown
                  (all null headers) aligns' widths' headers rows
            | hasSimpleCells &&
              isEnabled Ext_pipe_tables opts -> do
                rawHeaders <- padRow <$> mapM (blockListToMarkdown opts) headers
                rawRows <- mapM (fmap padRow . mapM (blockListToMarkdown opts))
                           rows
                (id,) <$> pipeTable (all null headers) aligns' rawHeaders rawRows
            | isEnabled Ext_raw_html opts -> fmap (id,) $
                   literal <$>
                   writeHtml5String opts{ writerTemplate = Nothing } (Pandoc nullMeta [t])
            | otherwise -> return (id, literal "[TABLE]")
  return $ nst (tbl $$ caption'') $$ blankline
blockToMarkdown' opts (BulletList items) = do
  contents <- inList $ mapM (bulletListItemToMarkdown opts) items
  return $ (if isTightList items then vcat else vsep) contents <> blankline
blockToMarkdown' opts (OrderedList (start,sty,delim) items) = do
  variant <- asks envVariant
  let start' = if variant == Commonmark || isEnabled Ext_startnum opts
                  then start
                  else 1
  let sty'   = if isEnabled Ext_fancy_lists opts then sty else DefaultStyle
  let delim' = if isEnabled Ext_fancy_lists opts then delim else DefaultDelim
  let attribs = (start', sty', delim')
  let markers  = orderedListMarkers attribs
  let markers' = map (\m -> if T.length m < 3
                               then m <> T.replicate (3 - T.length m) " "
                               else m) markers
  contents <- inList $
              zipWithM (orderedListItemToMarkdown opts) markers' items
  return $ (if isTightList items then vcat else vsep) contents <> blankline
blockToMarkdown' opts (DefinitionList items) = do
  contents <- inList $ mapM (definitionListItemToMarkdown opts) items
  return $ mconcat contents <> blankline

inList :: Monad m => MD m a -> MD m a
inList p = local (\env -> env {envInList = True}) p

addMarkdownAttribute :: Text -> Text
addMarkdownAttribute s =
  case span isTagText $ reverse $ parseTags s of
       (xs, TagOpen t attrs:rest) ->
            renderTags' $ reverse rest ++ (TagOpen t attrs' : reverse xs)
              where attrs' = ("markdown","1"):[(x,y) | (x,y) <- attrs,
                                 x /= "markdown"]
       _ -> s

pipeTable :: PandocMonad m
          => Bool -> [Alignment] -> [Doc Text] -> [[Doc Text]]
          -> MD m (Doc Text)
pipeTable headless aligns rawHeaders rawRows = do
  let sp = literal " "
  let blockFor AlignLeft   x y = lblock (x + 2) (sp <> y) <> lblock 0 empty
      blockFor AlignCenter x y = cblock (x + 2) (sp <> y <> sp) <> lblock 0 empty
      blockFor AlignRight  x y = rblock (x + 2) (y <> sp) <> lblock 0 empty
      blockFor _           x y = lblock (x + 2) (sp <> y) <> lblock 0 empty
  let widths = map (max 3 . maybe 3 maximum . nonEmpty . map offset) $
                     transpose (rawHeaders : rawRows)
  let torow cs = nowrap $ literal "|" <>
                    hcat (intersperse (literal "|") $
                          zipWith3 blockFor aligns widths (map chomp cs))
                    <> literal "|"
  let toborder a w = literal $ case a of
                          AlignLeft    -> ":" <> T.replicate (w + 1) "-"
                          AlignCenter  -> ":" <> T.replicate w "-" <> ":"
                          AlignRight   -> T.replicate (w + 1) "-" <> ":"
                          AlignDefault -> T.replicate (w + 2) "-"
  -- 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 $ literal "|" <> hcat (intersperse (literal "|") $
                        zipWith toborder aligns widths) <> literal "|"
  let body   = vcat $ map torow rawRows
  return $ header $$ border $$ body

pandocTable :: PandocMonad m
            => WriterOptions -> Bool -> Bool -> [Alignment] -> [Double]
            -> [Doc Text] -> [[Doc Text]] -> MD m (Doc Text)
pandocTable opts multiline headless aligns widths rawHeaders rawRows = do
  let isSimple = all (==0) widths
  let alignHeader alignment = case alignment of
                                AlignLeft    -> lblock
                                AlignCenter  -> cblock
                                AlignRight   -> rblock
                                AlignDefault -> lblock
  -- Number of characters per column necessary to output every cell
  -- without requiring a line break.
  -- The @+2@ is needed for specifying the alignment.
  let numChars    = (+ 2) . maybe 0 maximum . nonEmpty . map offset
  -- Number of characters per column necessary to output every cell
  -- without requiring a line break *inside a word*.
  -- The @+2@ is needed for specifying the alignment.
  let minNumChars = (+ 2) . maybe 0 maximum . nonEmpty . map minOffset
  let columns = transpose (rawHeaders : rawRows)
  -- minimal column width without wrapping a single word
  let relWidth w col =
         max (floor $ fromIntegral (writerColumns opts - 1) * w)
             (if writerWrapText opts == WrapAuto
                 then minNumChars col
                 else numChars col)
  let widthsInChars
        | isSimple  = map numChars columns
        | otherwise = zipWith relWidth widths columns
  let makeRow = hcat . intersperse (lblock 1 (literal " ")) .
                   zipWith3 alignHeader aligns widthsInChars
  let rows' = map makeRow rawRows
  let head' = makeRow rawHeaders
  let underline = mconcat $ intersperse (literal " ") $
                  map (\width -> literal (T.replicate width "-")) widthsInChars
  let border
        | multiline = literal (T.replicate (sum widthsInChars +
                        length widthsInChars - 1) "-")
        | headless  = underline
        | otherwise = empty
  let head'' = if headless
                  then empty
                  else border <> cr <> head'
  let body = if multiline
                then vsep rows' $$
                     if length rows' < 2
                        then blankline -- #4578
                        else empty
                else vcat rows'
  let bottom = if headless
                  then underline
                  else border
  return $ head'' $$ underline $$ body $$ bottom

itemEndsWithTightList :: [Block] -> Bool
itemEndsWithTightList bs =
  case bs of
        [Plain _, BulletList xs]    -> isTightList xs
        [Plain _, OrderedList _ xs] -> isTightList xs
        _                           -> False

-- | Convert bullet list item (list of blocks) to markdown.
bulletListItemToMarkdown :: PandocMonad m => WriterOptions -> [Block] -> MD m (Doc Text)
bulletListItemToMarkdown opts bs = do
  let exts = writerExtensions opts
  contents <- blockListToMarkdown opts $ taskListItemToAscii exts bs
  let sps = T.replicate (writerTabStop opts - 2) " "
  let start = literal $ "- " <> sps
  -- remove trailing blank line if item ends with a tight list
  let contents' = if itemEndsWithTightList bs
                     then chomp contents <> cr
                     else contents
  return $ hang (writerTabStop opts) start contents'

-- | Convert ordered list item (a list of blocks) to markdown.
orderedListItemToMarkdown :: PandocMonad m
                          => WriterOptions -- ^ options
                          -> Text        -- ^ list item marker
                          -> [Block]       -- ^ list item (list of blocks)
                          -> MD m (Doc Text)
orderedListItemToMarkdown opts marker bs = do
  let exts = writerExtensions opts
  contents <- blockListToMarkdown opts $ taskListItemToAscii exts bs
  let sps = case writerTabStop opts - T.length marker of
                   n | n > 0 -> literal $ T.replicate n " "
                   _ -> literal " "
  let ind = if isEnabled Ext_four_space_rule opts
               then writerTabStop opts
               else max (writerTabStop opts) (T.length marker + 1)
  let start = literal marker <> sps
  -- remove trailing blank line if item ends with a tight list
  let contents' = if itemEndsWithTightList bs
                     then chomp contents <> cr
                     else contents
  return $ hang ind start contents'

-- | Convert definition list item (label, list of blocks) to markdown.
definitionListItemToMarkdown :: PandocMonad m
                             => WriterOptions
                             -> ([Inline],[[Block]])
                             -> MD m (Doc Text)
definitionListItemToMarkdown opts (label, defs) = do
  labelText <- blockToMarkdown opts (Plain label)
  defs' <- mapM (mapM (blockToMarkdown opts)) defs
  if isEnabled Ext_definition_lists opts
     then do
       let tabStop = writerTabStop opts
       variant <- asks envVariant
       let leader  = if variant == PlainText then "   " else ":  "
       let sps = case writerTabStop opts - 3 of
                      n | n > 0   -> literal $ T.replicate n " "
                      _ -> literal " "
       let isTight = case defs of
                        ((Plain _ : _): _) -> True
                        _                  -> False
       if isEnabled Ext_compact_definition_lists opts
          then do
            let contents = vcat $ map (\d -> hang tabStop (leader <> sps)
                                $ vcat d <> cr) defs'
            return $ nowrap labelText <> cr <> contents <> cr
          else do
            let contents = (if isTight then vcat else vsep) $ map
                            (\d -> hang tabStop (leader <> sps) $ vcat d)
                            defs'
            return $ blankline <> nowrap labelText $$
                     (if isTight then empty else blankline) <> contents <> blankline
     else
       return $ nowrap (chomp labelText <> literal "  " <> cr) <>
                vsep (map vsep defs') <> blankline

-- | Convert list of Pandoc block elements to markdown.
blockListToMarkdown :: PandocMonad m
                    => WriterOptions -- ^ Options
                    -> [Block]       -- ^ List of block elements
                    -> MD m (Doc Text)
blockListToMarkdown opts blocks = do
  inlist <- asks envInList
  variant <- asks envVariant
  -- a) insert comment between list and indented code block, or the
  -- code block will be treated as a list continuation paragraph
  -- b) change Plain to Para unless it's followed by a RawBlock
  -- or has a list as its parent (#3487)
  let fixBlocks (b : CodeBlock attr x : rest)
       | (not (variant == Commonmark ||
               isEnabled Ext_backtick_code_blocks opts ||
                 isEnabled Ext_fenced_code_blocks opts) ||
              attr == nullAttr)
            && isListBlock b
              = b : commentSep : CodeBlock attr x : fixBlocks rest
      fixBlocks (b1@(BulletList _) : b2@(BulletList _) : bs) =
           b1 : commentSep : fixBlocks (b2:bs)
      fixBlocks (b1@(OrderedList _ _) : b2@(OrderedList _ _) : bs) =
           b1 : commentSep : fixBlocks (b2:bs)
      fixBlocks (b1@(DefinitionList _) : b2@(DefinitionList _) : bs) =
           b1 : commentSep : fixBlocks (b2:bs)
      fixBlocks (Plain ils : bs@(RawBlock{}:_)) =
           Plain ils : fixBlocks bs
      fixBlocks (Plain ils : bs) | inlist =
           Plain ils : fixBlocks bs
      fixBlocks (Plain ils : bs) =
           Para ils : fixBlocks bs
      fixBlocks (r@(RawBlock f raw) : b : bs)
        | not (T.null raw)
        , T.last raw /= '\n' =
        case b of
             Plain{}    -> r : fixBlocks (b:bs)
             RawBlock{} -> r : fixBlocks (b:bs)
             _          -> RawBlock f (raw <> "\n") : fixBlocks (b:bs) -- #4629
      fixBlocks (x : xs)             = x : fixBlocks xs
      fixBlocks []                   = []
      isListBlock (BulletList _)     = True
      isListBlock (OrderedList _ _)  = True
      isListBlock (DefinitionList _) = True
      isListBlock _                  = False
      commentSep
        | variant == PlainText        = Null
        | isEnabled Ext_raw_html opts = RawBlock "html" "<!-- -->\n"
        | otherwise                   = RawBlock "markdown" "&nbsp;\n"
  mconcat <$> mapM (blockToMarkdown opts) (fixBlocks blocks)

lineBreakToSpace :: Inline -> Inline
lineBreakToSpace LineBreak = Space
lineBreakToSpace SoftBreak = Space
lineBreakToSpace x         = x