Lua: use package pandoc-lua-marshal (#7719)

The marshaling functions for pandoc's AST are extracted into a separate
package. The package comes with a number of changes:

  - Pandoc's List module was rewritten in C, thereby improving error
    messages.

  - Lists of `Block` and `Inline` elements are marshaled using the new
    list types `Blocks` and `Inlines`, respectively. These types
    currently behave identical to the generic List type, but give better
    error messages. This also opens up the possibility of adding
    element-specific methods to these lists in the future.

  - Elements of type `MetaValue` are no longer pushed as values which
    have `.t` and `.tag` properties. This was already true for
    `MetaString` and `MetaBool` values, which are still marshaled as Lua
    strings and booleans, respectively. Affected values:

      + `MetaBlocks` values are marshaled as a `Blocks` list;

      + `MetaInlines` values are marshaled as a `Inlines` list;

      + `MetaList` values are marshaled as a generic pandoc `List`s.

      + `MetaMap` values are marshaled as plain tables and no longer
        given any metatable.

  - The test suite for marshaled objects and their constructors has
    been extended and improved.

  - A bug in Citation objects, where setting a citation's suffix
    modified it's prefix, has been fixed.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Lua/Marshal/Context.hs b/src/Text/Pandoc/Lua/Marshal/Context.hs
new file mode 100644
index 000000000..17af936e1
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Marshal/Context.hs
@@ -0,0 +1,28 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{- |
+   Module      : Text.Pandoc.Lua.Marshaling.Context
+   Copyright   : © 2012-2021 John MacFarlane
+                 © 2017-2021 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Marshaling instance for doctemplates Context and its components.
+-}
+module Text.Pandoc.Lua.Marshal.Context () where
+
+import qualified HsLua as Lua
+import HsLua (Pushable)
+import Text.DocTemplates (Context(..), Val(..), TemplateTarget)
+import Text.DocLayout (render)
+
+instance (TemplateTarget a, Pushable a) => Pushable (Context a) where
+  push (Context m) = Lua.push m
+
+instance (TemplateTarget a, Pushable a) => Pushable (Val a) where
+  push NullVal = Lua.push ()
+  push (BoolVal b) = Lua.push b
+  push (MapVal ctx) = Lua.push ctx
+  push (ListVal xs) = Lua.push xs
+  push (SimpleVal d) = Lua.push $ render Nothing d