Lua: support extensions in custom readers.

Like custom readers, like writers, can define the set of supported
extensions by setting a global. E.g.:

``` lua
reader_extensions = {
  smart = true,
  citations = false,
}
```

2 files changed, 6 insertions, 2 deletions

diff --git a/src/Text/Pandoc/App.hs b/src/Text/Pandoc/App.hs
index b4a9454e5..1290fc1c5 100644
--- a/src/Text/Pandoc/App.hs
+++ b/src/Text/Pandoc/App.hs
@@ -165,7 +165,11 @@ convertWithOpts' scriptingEngine istty datadir opts = do
 
   (reader, readerExts) <-
     if ".lua" `T.isSuffixOf` readerName
-       then (,mempty) <$> engineReadCustom scriptingEngine (T.unpack readerName)
+       then do
+            let scriptPath = T.unpack readerNameBase
+            (r, extsConf) <- engineReadCustom scriptingEngine scriptPath
+            rexts         <- Format.applyExtensionsDiff extsConf flvrd
+            return (r, rexts)
        else if optSandbox opts
                then case runPure (getReader flvrd) of
                       Left e -> throwError e
diff --git a/src/Text/Pandoc/Scripting.hs b/src/Text/Pandoc/Scripting.hs
index 0defa2f77..d4be7e377 100644
--- a/src/Text/Pandoc/Scripting.hs
+++ b/src/Text/Pandoc/Scripting.hs
@@ -36,7 +36,7 @@ data ScriptingEngine = ScriptingEngine
     -- ^ Use the scripting engine to run a filter.
 
   , engineReadCustom :: forall m. (PandocMonad m, MonadIO m)
-                     => FilePath -> m (Reader m)
+                     => FilePath -> m (Reader m, ExtensionsConfig)
     -- ^ Function to parse input into a 'Pandoc' document.
 
   , engineWriteCustom :: forall m. (PandocMonad m, MonadIO m)