Org: support task_lists extension

The tasks lists extension is now supported by the org reader and writer;
the extension is turned on by default.

Closes: #6336

3 files changed, 54 insertions, 5 deletions

diff --git a/src/Text/Pandoc/Extensions.hs b/src/Text/Pandoc/Extensions.hs
index 82eb0e957..3b96f9e04 100644
--- a/src/Text/Pandoc/Extensions.hs
+++ b/src/Text/Pandoc/Extensions.hs
@@ -381,6 +381,7 @@ getDefaultExtensions "commonmark_x"    = extensionsFromList
   ]
 getDefaultExtensions "org"             = extensionsFromList
                                           [Ext_citations,
+                                           Ext_task_lists,
                                            Ext_auto_identifiers]
 getDefaultExtensions "html"            = extensionsFromList
                                           [Ext_auto_identifiers,
@@ -515,6 +516,7 @@ getAllExtensions f = universalExtensions <> getAll f
     extensionsFromList
     [ Ext_citations
     , Ext_smart
+    , Ext_task_lists
     ]
   getAll "html"            = autoIdExtensions <>
     extensionsFromList
diff --git a/src/Text/Pandoc/Readers/Org/Blocks.hs b/src/Text/Pandoc/Readers/Org/Blocks.hs
index 6bd046e04..d1aff701e 100644
--- a/src/Text/Pandoc/Readers/Org/Blocks.hs
+++ b/src/Text/Pandoc/Readers/Org/Blocks.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE FlexibleContexts  #-}
-{-# LANGUAGE RecordWildCards   #-}
+{-# LANGUAGE LambdaCase        #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards   #-}
 {- |
    Module      : Text.Pandoc.Readers.Org.Blocks
    Copyright   : Copyright (C) 2014-2021 Albert Krewinkel
@@ -850,16 +851,52 @@ definitionListItem parseIndentedMarker = try $ do
    definitionMarker =
      spaceChar *> string "::" <* (spaceChar <|> lookAhead newline)
 
+-- | Checkbox for tasks.
+data Checkbox
+  = UncheckedBox
+  | CheckedBox
+  | SemicheckedBox
+
+-- | Parses a checkbox in a plain list.
+checkbox :: PandocMonad m
+         => OrgParser m Checkbox
+checkbox = do
+  guardEnabled Ext_task_lists
+  try (char '[' *> status <* char ']') <?> "checkbox"
+  where
+    status = choice
+      [ UncheckedBox   <$ char ' '
+      , CheckedBox     <$ char 'X'
+      , SemicheckedBox <$ char '-'
+      ]
+
+checkboxToInlines :: Checkbox -> Inline
+checkboxToInlines = B.Str . \case
+  UncheckedBox   -> "☐"
+  SemicheckedBox -> "☐"
+  CheckedBox     -> "☒"
+
 -- | parse raw text for one list item
 listItem :: PandocMonad m
          => OrgParser m Int
          -> OrgParser m (F Blocks)
 listItem parseIndentedMarker = try . withContext ListItemState $ do
   markerLength <- try parseIndentedMarker
+  box <- optionMaybe checkbox
   firstLine <- anyLineNewline
   blank <- option "" ("\n" <$ blankline)
   rest <- T.concat <$> many (listContinuation markerLength)
-  parseFromString blocks $ firstLine <> blank <> rest
+  contents <- parseFromString blocks $ firstLine <> blank <> rest
+  return (maybe id (prependInlines . checkboxToInlines) box <$> contents)
+
+-- | Prepend inlines to blocks, adding them to the first paragraph or
+-- creating a new Plain element if necessary.
+prependInlines :: Inline -> Blocks -> Blocks
+prependInlines inlns = B.fromList . prepend . B.toList
+  where
+    prepend (Plain is : bs) = Plain (inlns : Space : is) : bs
+    prepend (Para  is : bs) = Para  (inlns : Space : is) : bs
+    prepend bs              = Plain [inlns, Space] : bs
 
 -- continuation of a list item - indented and separated by blankline or endline.
 -- Note: nested lists are parsed as continuations.
diff --git a/src/Text/Pandoc/Writers/Org.hs b/src/Text/Pandoc/Writers/Org.hs
index 43ebf1807..8dfc2749c 100644
--- a/src/Text/Pandoc/Writers/Org.hs
+++ b/src/Text/Pandoc/Writers/Org.hs
@@ -213,25 +213,35 @@ blockToOrg (DefinitionList items) = do
 -- | Convert bullet list item (list of blocks) to Org.
 bulletListItemToOrg :: PandocMonad m => [Block] -> Org m (Doc Text)
 bulletListItemToOrg items = do
-  contents <- blockListToOrg items
+  exts <- gets $ writerExtensions . stOptions
+  contents <- blockListToOrg (taskListItemToOrg exts items)
   return $ hang 2 "- " contents $$
           if endsWithPlain items
              then cr
              else blankline
 
-
 -- | Convert ordered list item (a list of blocks) to Org.
 orderedListItemToOrg :: PandocMonad m
                      => Text   -- ^ marker for list item
                      -> [Block]  -- ^ list item (list of blocks)
                      -> Org m (Doc Text)
 orderedListItemToOrg marker items = do
-  contents <- blockListToOrg items
+  exts <- gets $ writerExtensions . stOptions
+  contents <- blockListToOrg (taskListItemToOrg exts items)
   return $ hang (T.length marker + 1) (literal marker <> space) contents $$
           if endsWithPlain items
              then cr
              else blankline
 
+-- | Convert a list item containing text starting with @U+2610 BALLOT BOX@
+-- or @U+2612 BALLOT BOX WITH X@ to org checkbox syntax (e.g. @[X]@).
+taskListItemToOrg :: Extensions -> [Block] -> [Block]
+taskListItemToOrg = handleTaskListItem toOrg
+  where
+    toOrg (Str "☐" : Space : is) = Str "[ ]" : Space : is
+    toOrg (Str "☒" : Space : is) = Str "[X]" : Space : is
+    toOrg is = is
+
 -- | Convert definition list item (label, list of blocks) to Org.
 definitionListItemToOrg :: PandocMonad m
                         => ([Inline], [[Block]]) -> Org m (Doc Text)