[API Change] Base custom writers on Writer type.

The `T.P.Lua.writeCustom` function changed to allow either a TextWriter
or ByteStringWriter to be returned. The global variables
`PANDOC_DOCUMENT` and `PANDOC_WRITER_OPTIONS` are no longer set when the
writer script is loaded. Both variables are still set in classic writers
before the conversion is started, so they can be used when they are
wrapped in functions.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/Text/Pandoc/Scripting.hs b/src/Text/Pandoc/Scripting.hs
index ce171c81a..17bc2f972 100644
--- a/src/Text/Pandoc/Scripting.hs
+++ b/src/Text/Pandoc/Scripting.hs
@@ -22,8 +22,9 @@ import Text.Pandoc.Definition (Pandoc)
 import Text.Pandoc.Class.PandocMonad (PandocMonad)
 import Text.Pandoc.Error (PandocError (PandocNoScriptingEngine))
 import Text.Pandoc.Filter.Environment (Environment)
-import Text.Pandoc.Options (ReaderOptions, WriterOptions)
+import Text.Pandoc.Options (ReaderOptions)
 import Text.Pandoc.Sources (Sources)
+import Text.Pandoc.Writers (Writer)
 
 -- | Structure to define a scripting engine.
 data ScriptingEngine = ScriptingEngine
@@ -39,7 +40,7 @@ data ScriptingEngine = ScriptingEngine
     -- ^ Function to parse input into a 'Pandoc' document.
 
   , engineWriteCustom :: forall m. (PandocMonad m, MonadIO m)
-                      => FilePath -> WriterOptions -> Pandoc -> m Text
+                      => FilePath -> m (Writer m)
     -- ^ Invoke the given script file to convert to any custom format.
   }
 
@@ -50,6 +51,6 @@ noEngine = ScriptingEngine
       throwError PandocNoScriptingEngine
   , engineReadCustom = \_fp _ropts _sources ->
       throwError PandocNoScriptingEngine
-  , engineWriteCustom = \_fp _wopts _doc ->
+  , engineWriteCustom = \_fp ->
       throwError PandocNoScriptingEngine
   }