Implemented fenced Divs.

+ Added Ext_fenced_divs to Extensions (default for pandoc Markdown).
+ Document fenced_divs extension in manual.
+ Implemented fenced code divs in Markdown reader.
+ Added test.

Closes #168.

MANUAL.txt

@@ -3073,6 +3073,37 @@ For the most part this should give the same output as `raw_html`,
 but it makes it easier to write pandoc filters to manipulate groups
 of inlines.
 
+#### Extension: `fenced_divs` ####
+
+Allow special fenced syntax for native `Div` blocks.  A Div
+starts with a fence containing at least three consecutive
+colons plus some attributes. The attributes may optionally
+be followed by another string of consecutive colons.
+The attribute syntax is exactly as in fenced code blocks (see
+[Extension-fenced_code_attributes], above).  The Div ends with
+another line containing a string of at least three consecutive
+colons.  The fenced Div should be separated by blank lines from
+preceding and following blocks.
+
+Example:
+
+    ::::: {#special .sidebar}
+    Here is a paragraph.
+
+    And another.
+    :::::
+
+Fenced divs can be nested.  Opening fences are distinguished
+because they *must* have attributes:
+
+    ::: Warning
+    This is a warning.
+
+    ::: Danger
+    This is a warning within a warning.
+    :::
+    :::
+
 #### Extension: `raw_tex` ####
 
 In addition to raw HTML, pandoc allows raw LaTeX, TeX, and ConTeXt to be

src/Text/Pandoc/Extensions.hs

@@ -107,6 +107,7 @@ data Extension =
     | Ext_raw_attribute           -- ^ Allow explicit raw blocks/inlines
     | Ext_markdown_in_html_blocks -- ^ Interpret as markdown inside HTML blocks
     | Ext_native_divs             -- ^ Use Div blocks for contents of <div> tags
+    | Ext_fenced_divs             -- ^ Allow fenced div syntax :::
     | Ext_native_spans            -- ^ Use Span inlines for contents of <span>
     | Ext_bracketed_spans         -- ^ Bracketed spans with attributes
     | Ext_markdown_attribute      -- ^ Interpret text inside HTML as markdown
@@ -183,6 +184,7 @@ pandocExtensions = extensionsFromList
   , Ext_raw_attribute
   , Ext_markdown_in_html_blocks
   , Ext_native_divs
+  , Ext_fenced_divs
   , Ext_native_spans
   , Ext_bracketed_spans
   , Ext_escaped_line_breaks

src/Text/Pandoc/Parsing.hs

@@ -1069,6 +1069,7 @@ data ParserState = ParserState
       -- roles), 3) Additional classes (rest of Attr is unused)).
       stateCaption         :: Maybe Inlines, -- ^ Caption in current environment
       stateInHtmlBlock     :: Maybe String,  -- ^ Tag type of HTML block being parsed
+      stateFencedDivLevel  :: Int,           -- ^ Depth of fenced div
       stateContainers      :: [String],      -- ^ parent include files
       stateLogMessages     :: [LogMessage],  -- ^ log messages
       stateMarkdownAttribute :: Bool         -- ^ True if in markdown=1 context
@@ -1185,6 +1186,7 @@ defaultParserState =
                   stateRstCustomRoles  = M.empty,
                   stateCaption         = Nothing,
                   stateInHtmlBlock     = Nothing,
+                  stateFencedDivLevel  = 0,
                   stateContainers      = [],
                   stateLogMessages     = [],
                   stateMarkdownAttribute = False

src/Text/Pandoc/Readers/Markdown.hs

@@ -499,6 +499,7 @@ block = do
                , header
                , lhsCodeBlock
                , divHtml
+               , divFenced
                , htmlBlock
                , table
                , codeBlockIndented
@@ -1686,6 +1687,9 @@ endline = try $ do
   guardEnabled Ext_blank_before_header <|> (notFollowedBy . char =<< atxChar) -- atx header
   guardDisabled Ext_backtick_code_blocks <|>
      notFollowedBy (() <$ (lookAhead (char '`') >> codeBlockFenced))
+  guardDisabled Ext_fenced_divs <|>
+    do divLevel <- stateFencedDivLevel <$> getState
+       guard (divLevel < 1) <|> notFollowedBy fenceEnd
   notFollowedByHtmlCloser
   (eof >> return mempty)
     <|> (guardEnabled Ext_hard_line_breaks >> return (return B.linebreak))
@@ -1930,6 +1934,30 @@ divHtml = try $ do
      else -- avoid backtracing
        return $ return (B.rawBlock "html" (rawtag <> bls)) <> contents
 
+divFenced :: PandocMonad m => MarkdownParser m (F Blocks)
+divFenced = try $ do
+  guardEnabled Ext_fenced_divs
+  nonindentSpaces
+  string ":::"
+  skipMany (char ':')
+  skipMany spaceChar
+  attribs <- attributes <|> ((\x -> ("",[x],[])) <$> many1 nonspaceChar)
+  skipMany spaceChar
+  skipMany (char ':')
+  blankline
+  updateState $ \st -> st{ stateFencedDivLevel = stateFencedDivLevel st + 1 }
+  bs <- mconcat <$> manyTill block fenceEnd
+  updateState $ \st -> st{ stateFencedDivLevel = stateFencedDivLevel st - 1 }
+  return $ B.divWith attribs <$> bs
+
+fenceEnd :: PandocMonad m => MarkdownParser m ()
+fenceEnd = try $ do
+  nonindentSpaces
+  string ":::"
+  skipMany (char ':')
+  blanklines
+  return ()
+
 rawHtmlInline :: PandocMonad m => MarkdownParser m (F Inlines)
 rawHtmlInline = do
   guardEnabled Ext_raw_html

test/command/168.md

@@ -0,0 +1,30 @@
+```
+% pandoc -t native
+:::::::::: warning ::::::::::::
+This is the warning!
+
+1. list
+2. another
+
+::: {#myid .class key=val}
+nested div
+:::
+:::::::::::::::::::::::::::::::
+^D
+[Div ("",["warning"],[])
+ [Para [Str "This",Space,Str "is",Space,Str "the",Space,Str "warning!"]
+ ,OrderedList (1,Decimal,Period)
+  [[Plain [Str "list"]]
+  ,[Plain [Str "another"]]]
+ ,Div ("myid",["class"],[("key","val")])
+  [Plain [Str "nested",Space,Str "div"]]]]
+```
+
+```
+% pandoc -t native
+foo
+:::
+bar
+^D
+[Para [Str "foo",SoftBreak,Str ":::",SoftBreak,Str "bar"]]
+```