Lua: ensure that tables marshaled via JSON arrays behave like Lists.

This allows to invoke methods like `map` and `includes` on lists like
`PANDOC_WRITER_OPTIONS.extensions`.

pandoc.cabal

@@ -540,9 +540,10 @@ library
     build-depends:  template-haskell
   if flag(lua53)
     build-depends:  hslua >= 2.1 && < 2.2,
-                    hslua-aeson >= 2.1 && < 2.3
+                    hslua-aeson >= 2.2.1 && < 2.3
   else
     build-depends:  hslua >= 2.2.1 && < 2.3
+                  , hslua-aeson >= 2.2.1 && < 2.3
   if flag(embed_data_files)
      cpp-options:   -DEMBED_DATA_FILES
      other-modules: Text.Pandoc.Data

src/Text/Pandoc/Lua/Init.hs

@@ -21,11 +21,12 @@ import Data.Maybe (catMaybes)
 import HsLua as Lua hiding (status, try)
 import Text.Pandoc.Class.PandocMonad (PandocMonad, readDataFile)
 import Text.Pandoc.Error (PandocError (PandocLuaError))
-import Text.Pandoc.Lua.Marshal.List (pushListModule)
+import Text.Pandoc.Lua.Marshal.List (newListMetatable, pushListModule)
 import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua, runPandocLua)
 import qualified Data.ByteString.Char8 as Char8
 import qualified Data.Text as T
 import qualified Lua.LPeg as LPeg
+import qualified HsLua.Aeson
 import qualified HsLua.Module.DocLayout as Module.Layout
 import qualified HsLua.Module.Path as Module.Path
 import qualified HsLua.Module.Text as Module.Text
@@ -66,6 +67,7 @@ loadedModules =
 initLuaState :: PandocLua ()
 initLuaState = do
   liftPandocLua Lua.openlibs
+  initJsonMetatable
   initPandocModule
   installLpegSearcher
   setGlobalModules
@@ -143,3 +145,9 @@ 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
+
+-- | Setup the metatable that's assigned to Lua tables that were created
+-- from/via JSON arrays.
+initJsonMetatable :: PandocLua ()
+initJsonMetatable = liftPandocLua $ do
+  newListMetatable HsLua.Aeson.jsonarray (pure ())

stack.yaml

@@ -12,7 +12,7 @@ extra-deps:
 - emojis-0.1.2
 - lpeg-1.0.3
 - hslua-2.2.1
-- hslua-aeson-2.2.0
+- hslua-aeson-2.2.1
 - hslua-classes-2.2.0
 - hslua-core-2.2.1
 - hslua-marshalling-2.2.1