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, 20 insertions, 30 deletions

diff --git a/src/Text/Pandoc/Lua/Init.hs b/src/Text/Pandoc/Lua/Init.hs
index 2f113bff2..835da1fc9 100644
--- a/src/Text/Pandoc/Lua/Init.hs
+++ b/src/Text/Pandoc/Lua/Init.hs
@@ -17,7 +17,6 @@ module Text.Pandoc.Lua.Init
 import Control.Monad (forM, forM_, when)
 import Control.Monad.Catch (throwM, try)
 import Control.Monad.Trans (MonadIO (..))
-import Data.Data (Data, dataTypeConstrs, dataTypeOf, showConstr)
 import Data.Maybe (catMaybes)
 import HsLua as Lua hiding (status, try)
 import GHC.IO.Encoding (getForeignEncoding, setForeignEncoding, utf8)
@@ -27,7 +26,6 @@ import Text.Pandoc.Lua.Packages (installPandocPackageSearcher)
 import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua, runPandocLua)
 import qualified Data.Text as T
 import qualified Lua.LPeg as LPeg
-import qualified Text.Pandoc.Definition as Pandoc
 import qualified Text.Pandoc.Lua.Module.Pandoc as ModulePandoc
 
 -- | Run the lua interpreter, using pandoc's default way of environment
@@ -42,6 +40,19 @@ runLua luaOp = do
   liftIO $ setForeignEncoding enc
   return res
 
+-- | Modules that are loaded at startup and assigned to fields in the
+-- pandoc module.
+loadedModules :: [(Name, Name)]
+loadedModules =
+  [ ("pandoc.List", "List")
+  , ("pandoc.mediabag", "mediabag")
+  , ("pandoc.path", "path")
+  , ("pandoc.system", "system")
+  , ("pandoc.types", "types")
+  , ("pandoc.utils", "utils")
+  , ("text", "text")
+  ]
+
 -- | Initialize the lua state with all required values
 initLuaState :: PandocLua ()
 initLuaState = do
@@ -61,9 +72,13 @@ initLuaState = do
       Lua.getfield Lua.registryindex Lua.loaded
       Lua.pushvalue (Lua.nth 2)
       Lua.setfield (Lua.nth 2) "pandoc"
-      Lua.pop 1
-    -- copy constructors into registry
-    putConstructorsInRegistry
+      Lua.pop 1  -- remove LOADED table
+    -- load modules and add them to the `pandoc` module table.
+    liftPandocLua $ forM_ loadedModules $ \(pkgname, fieldname) -> do
+      Lua.getglobal "require"
+      Lua.pushName pkgname
+      Lua.call 1 1
+      Lua.setfield (nth 2) fieldname
     -- assign module to global variable
     liftPandocLua $ Lua.setglobal "pandoc"
 
@@ -122,28 +137,3 @@ initLuaState = do
     Lua.pushHaskellFunction $ Lua.state >>= liftIO . LPeg.lpeg_searcher
     Lua.rawseti (Lua.nth 2) . (+1) . fromIntegral =<< Lua.rawlen (Lua.nth 2)
     Lua.pop 1  -- remove 'package.searchers' from stack
-
--- | AST elements are marshaled via normal constructor functions in the
--- @pandoc@ module. However, accessing Lua globals from Haskell is
--- expensive (due to error handling). Accessing the Lua registry is much
--- cheaper, which is why the constructor functions are copied into the
--- Lua registry and called from there.
---
--- This function expects the @pandoc@ module to be at the top of the
--- stack.
-putConstructorsInRegistry :: PandocLua ()
-putConstructorsInRegistry = liftPandocLua $ do
-  constrsToReg $ Pandoc.Meta mempty
-  constrsToReg $ Pandoc.MetaList mempty
-  putInReg "List"  -- pandoc.List
-  putInReg "SimpleTable"  -- helper for backward-compatible table handling
- where
-  constrsToReg :: Data a => a -> LuaE PandocError ()
-  constrsToReg = mapM_ (putInReg . showConstr) . dataTypeConstrs . dataTypeOf
-
-  putInReg :: String -> LuaE PandocError ()
-  putInReg name = do
-    Lua.push ("pandoc." ++ name) -- name in registry
-    Lua.push name -- in pandoc module
-    Lua.rawget (Lua.nth 3)
-    Lua.rawset Lua.registryindex