Lua filters: add SimpleTable for backwards compatibility (#6575)

A new type `SimpleTable` is made available to Lua filters. It is
similar to the `Table` type in pandoc versions before 2.10;
conversion functions from and to the new Table type are provided.

Old filters using tables now require minimal changes and can use,
e.g.,

    if PANDOC_VERSION > {2,10,1} then
      pandoc.Table = pandoc.SimpleTable
    end

and

    function Table (tbl)
      tbl = pandoc.utils.to_simple_table(tbl)
      …
      return pandoc.utils.from_simple_table(tbl)
    end

to work with the current pandoc version.

5 files changed, 106 insertions, 7 deletions

diff --git a/src/Text/Pandoc/Lua/Init.hs b/src/Text/Pandoc/Lua/Init.hs
index a5e513a1f..e89e9d6e0 100644
--- a/src/Text/Pandoc/Lua/Init.hs
+++ b/src/Text/Pandoc/Lua/Init.hs
@@ -80,6 +80,7 @@ putConstructorsInRegistry = liftPandocLua $ do
   putInReg "Attr"  -- used for Attr type alias
   putInReg "ListAttributes"  -- used for ListAttributes type alias
   putInReg "List"  -- pandoc.List
+  putInReg "SimpleTable"  -- helper for backward-compatible table handling
  where
   constrsToReg :: Data a => a -> Lua ()
   constrsToReg = mapM_ (putInReg . showConstr) . dataTypeConstrs . dataTypeOf
diff --git a/src/Text/Pandoc/Lua/Marshaling/AST.hs b/src/Text/Pandoc/Lua/Marshaling/AST.hs
index 679dd1f46..c889618c4 100644
--- a/src/Text/Pandoc/Lua/Marshaling/AST.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/AST.hs
@@ -260,7 +260,7 @@ instance Peekable TableBody where
     return $ TableBody attr (RowHeadColumns rowHeadColumns) head' body
 
 instance Pushable TableHead where
-  push (TableHead attr cells) = Lua.push (attr, cells)
+  push (TableHead attr rows) = Lua.push (attr, rows)
 
 instance Peekable TableHead where
   peek = fmap (uncurry TableHead) . Lua.peek
diff --git a/src/Text/Pandoc/Lua/Marshaling/SimpleTable.hs b/src/Text/Pandoc/Lua/Marshaling/SimpleTable.hs
new file mode 100644
index 000000000..98fa1efa4
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Marshaling/SimpleTable.hs
@@ -0,0 +1,59 @@
+{- |
+   Module      : Text.Pandoc.Lua.Marshaling.SimpleTable
+   Copyright   : © 2020 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Definition and marshaling of the 'SimpleTable' data type used as a
+convenience type when dealing with tables.
+-}
+module Text.Pandoc.Lua.Marshaling.SimpleTable
+  ( SimpleTable (..)
+  , peekSimpleTable
+  , pushSimpleTable
+  )
+  where
+
+import Foreign.Lua (Lua, Peekable, Pushable, StackIndex)
+import Text.Pandoc.Definition
+import Text.Pandoc.Lua.Util (defineHowTo, pushViaConstructor, rawField)
+import Text.Pandoc.Lua.Marshaling.AST ()
+
+import qualified Foreign.Lua as Lua
+
+-- | A simple (legacy-style) table.
+data SimpleTable = SimpleTable
+  { simpleTableCaption :: [Inline]
+  , simpleTableAlignments :: [Alignment]
+  , simpleTableColumnWidths :: [Double]
+  , simpleTableHeader :: [[Block]]
+  , simpleTableBody :: [[[Block]]]
+  }
+
+instance Pushable SimpleTable where
+  push = pushSimpleTable
+
+instance Peekable SimpleTable where
+  peek = peekSimpleTable
+
+-- | Push a simple table to the stack by calling the
+-- @pandoc.SimpleTable@ constructor.
+pushSimpleTable :: SimpleTable -> Lua ()
+pushSimpleTable tbl = pushViaConstructor "SimpleTable"
+  (simpleTableCaption tbl)
+  (simpleTableAlignments tbl)
+  (simpleTableColumnWidths tbl)
+  (simpleTableHeader tbl)
+  (simpleTableBody tbl)
+
+-- | Retrieve a simple table from the stack.
+peekSimpleTable :: StackIndex -> Lua SimpleTable
+peekSimpleTable idx = defineHowTo "get SimpleTable" $
+  SimpleTable
+    <$> rawField idx "caption"
+    <*> rawField idx "aligns"
+    <*> rawField idx "widths"
+    <*> rawField idx "headers"
+    <*> rawField idx "rows"
diff --git a/src/Text/Pandoc/Lua/Module/Utils.hs b/src/Text/Pandoc/Lua/Module/Utils.hs
index 988489a2a..7595b9c0f 100644
--- a/src/Text/Pandoc/Lua/Module/Utils.hs
+++ b/src/Text/Pandoc/Lua/Module/Utils.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {- |
    Module      : Text.Pandoc.Lua.Module.Utils
@@ -7,7 +8,7 @@
    Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
    Stability   : alpha
 
-Utility module for lua, exposing internal helper functions.
+Utility module for Lua, exposing internal helper functions.
 -}
 module Text.Pandoc.Lua.Module.Utils
   ( pushModule
@@ -15,13 +16,17 @@ module Text.Pandoc.Lua.Module.Utils
 
 import Control.Applicative ((<|>))
 import Control.Monad.Catch (try)
+import Data.Data (showConstr, toConstr)
 import Data.Default (def)
 import Data.Version (Version)
-import Foreign.Lua (Peekable, Lua, NumResults)
-import Text.Pandoc.Definition ( Pandoc, Meta, MetaValue (..), Block, Inline
-                              , Citation, Attr, ListAttributes)
+import Foreign.Lua (Peekable, Lua, NumResults (..))
+import Text.Pandoc.Definition
 import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Marshaling ()
+import Text.Pandoc.Lua.Marshaling.SimpleTable
+  ( SimpleTable (..)
+  , pushSimpleTable
+  )
 import Text.Pandoc.Lua.PandocLua (PandocLua, addFunction, liftPandocLua)
 
 import qualified Data.Digest.Pure.SHA as SHA
@@ -31,19 +36,22 @@ import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Builder as B
 import qualified Text.Pandoc.Filter.JSON as JSONFilter
 import qualified Text.Pandoc.Shared as Shared
+import qualified Text.Pandoc.Writers.Shared as Shared
 
--- | Push the "pandoc.utils" module to the lua stack.
+-- | Push the "pandoc.utils" module to the Lua stack.
 pushModule :: PandocLua NumResults
 pushModule = do
   liftPandocLua Lua.newtable
   addFunction "blocks_to_inlines" blocksToInlines
   addFunction "equals" equals
+  addFunction "from_simple_table" from_simple_table
   addFunction "make_sections" makeSections
   addFunction "normalize_date" normalizeDate
   addFunction "run_json_filter" runJSONFilter
   addFunction "sha1" sha1
   addFunction "stringify" stringify
   addFunction "to_roman_numeral" toRomanNumeral
+  addFunction "to_simple_table" to_simple_table
   addFunction "Version" (return :: Version -> Lua Version)
   return 1
 
@@ -131,6 +139,37 @@ instance Peekable AstElement where
       Left (_ :: PandocError) -> Lua.throwMessage
         "Expected an AST element, but could not parse value as such."
 
+-- | Converts an old/simple table into a normal table block element.
+from_simple_table :: SimpleTable -> Lua NumResults
+from_simple_table (SimpleTable capt aligns widths head' body) = do
+  Lua.push $ Table
+    nullAttr
+    (Caption Nothing [Plain capt])
+    (zipWith (\a w -> (a, toColWidth w)) aligns widths)
+    (TableHead nullAttr [blockListToRow head'])
+    [TableBody nullAttr 0 [] $ map blockListToRow body]
+    (TableFoot nullAttr [])
+  return (NumResults 1)
+  where
+    blockListToRow :: [[Block]] -> Row
+    blockListToRow = Row nullAttr . map (B.simpleCell . B.fromList)
+
+    toColWidth :: Double -> ColWidth
+    toColWidth 0 = ColWidthDefault
+    toColWidth w = ColWidth w
+
+-- | Converts a table into an old/simple table.
+to_simple_table :: Block -> Lua NumResults
+to_simple_table = \case
+  Table _attr caption specs thead tbodies tfoot -> do
+    let (capt, aligns, widths, headers, rows) =
+          Shared.toLegacyTable caption specs thead tbodies tfoot
+    pushSimpleTable $ SimpleTable capt aligns widths headers rows
+    return (NumResults 1)
+  blk ->
+    Lua.throwMessage $
+      "Expected Table, got " <> showConstr (toConstr blk) <> "."
+
 -- | Convert a number < 4000 to uppercase roman numeral.
 toRomanNumeral :: Lua.Integer -> PandocLua T.Text
 toRomanNumeral = return . Shared.toRomanNumeral . fromIntegral
diff --git a/src/Text/Pandoc/Lua/Util.hs b/src/Text/Pandoc/Lua/Util.hs
index c6639e94c..fbd013801 100644
--- a/src/Text/Pandoc/Lua/Util.hs
+++ b/src/Text/Pandoc/Lua/Util.hs
@@ -80,7 +80,7 @@ instance (Pushable a, PushViaCall b) => PushViaCall (a -> b) where
 pushViaCall :: PushViaCall a => String -> a
 pushViaCall fn = pushViaCall' fn (return ()) 0
 
--- | Call a pandoc element constructor within lua, passing all given arguments.
+-- | Call a pandoc element constructor within Lua, passing all given arguments.
 pushViaConstructor :: PushViaCall a => String -> a
 pushViaConstructor pandocFn = pushViaCall ("pandoc." ++ pandocFn)