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, 51 insertions, 0 deletions

diff --git a/src/Text/Pandoc/Lua/Marshal/PandocError.hs b/src/Text/Pandoc/Lua/Marshal/PandocError.hs
new file mode 100644
index 000000000..d1c0ad4f4
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Marshal/PandocError.hs
@@ -0,0 +1,51 @@
+{-# LANGUAGE LambdaCase           #-}
+{-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE ScopedTypeVariables  #-}
+{-# LANGUAGE TypeApplications     #-}
+{- |
+   Module      : Text.Pandoc.Lua.Marshal.PandocError
+   Copyright   : © 2020-2021 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Marshal of @'PandocError'@ values.
+-}
+module Text.Pandoc.Lua.Marshal.PandocError
+  ( peekPandocError
+  , pushPandocError
+  , typePandocError
+  )
+  where
+
+import HsLua.Core (LuaError)
+import HsLua.Marshalling (Peeker, Pusher, pushString, liftLua)
+import HsLua.Packaging
+import Text.Pandoc.Error (PandocError (PandocLuaError))
+
+import qualified HsLua as Lua
+import qualified Text.Pandoc.UTF8 as UTF8
+
+-- | Lua userdata type definition for PandocError.
+typePandocError :: LuaError e => DocumentedType e PandocError
+typePandocError = deftype "PandocError"
+  [ operation Tostring $ defun "__tostring"
+    ### liftPure (show @PandocError)
+    <#> udparam typePandocError "obj" "PandocError object"
+    =#> functionResult pushString "string" "string representation of error."
+  ]
+  mempty -- no members
+
+-- | Peek a @'PandocError'@ element to the Lua stack.
+pushPandocError :: LuaError e => Pusher e PandocError
+pushPandocError = pushUD typePandocError
+
+-- | Retrieve a @'PandocError'@ from the Lua stack.
+peekPandocError :: LuaError e => Peeker e PandocError
+peekPandocError idx = Lua.retrieving "PandocError" $
+  liftLua (Lua.ltype idx) >>= \case
+    Lua.TypeUserdata -> peekUD typePandocError idx
+    _ -> do
+      msg <- liftLua $ Lua.state >>= \l -> Lua.liftIO (Lua.popErrorMessage l)
+      return $ PandocLuaError (UTF8.toText msg)