Lua: support `-D` CLI option for custom writers [API change]

A new error `PandocNoTemplateError` (code 87) is thrown if a template is
required but cannot be found.

8 files changed, 43 insertions, 37 deletions

diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Writer.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Writer.hs
index c5e3e2469..91573c87b 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Writer.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Writer.hs
@@ -31,15 +31,13 @@ import Text.Pandoc.Format (ExtensionsConfig (..))
 import Text.Pandoc.Lua.Global (Global (..), setGlobals)
 import Text.Pandoc.Lua.Init (runLuaWith)
 import Text.Pandoc.Lua.Marshal.Format (peekExtensionsConfig)
-import Text.Pandoc.Lua.Marshal.Template (peekTemplate)
 import Text.Pandoc.Lua.Marshal.WriterOptions (pushWriterOptions)
-import Text.Pandoc.Templates (Template)
 import Text.Pandoc.Writers (Writer (..))
 import qualified Text.Pandoc.Lua.Writer.Classic as Classic
 
 -- | Convert Pandoc to custom markup.
 writeCustom :: (PandocMonad m, MonadIO m)
-            => FilePath -> m (Writer m, ExtensionsConfig, m (Template Text))
+            => FilePath -> m (Writer m, ExtensionsConfig, Maybe Text)
 writeCustom luaFile = do
   luaState <- liftIO newGCManagedState
   luaFile' <- fromMaybe luaFile <$> findFileWithDataFallback "writers" luaFile
@@ -66,19 +64,15 @@ writeCustom luaFile = do
       TypeNil   -> ExtensionsConfig mempty mempty <$ pop 1
       _         -> forcePeek $ peekExtensionsConfig top `lastly` pop 1
 
-    -- Store template function in registry
-    let templateField = "Pandoc Writer Template"
-    rawgetglobal "Template" *> setfield registryindex templateField
+    mtemplate <- rawgetglobal "Template" >>= \case
+      TypeNil   -> pure Nothing
+      TypeFunction -> Just <$> do
+        callTrace 0 1
+        forcePeek $ peekText top `lastly` pop 1
+      _ -> Just <$> do
+        forcePeek $ peekText top `lastly` pop 1
 
-    let getTemplate = liftIO $ withGCManagedState @PandocError luaState $ do
-          getfield registryindex templateField >>= \case
-            TypeNil   -> failLua $ "No default template for writer; " <>
-                         "the global variable Template is undefined."
-            _ -> do
-              callTrace 0 1
-              forcePeek $ peekTemplate top `lastly` pop 1
-
-    let addProperties = (, extsConf, getTemplate)
+    let addProperties = (, extsConf, mtemplate)
 
     rawgetglobal "Writer" >>= \case
       TypeNil -> rawgetglobal "ByteStringWriter" >>= \case
diff --git a/pandoc-lua-engine/test/Tests/Lua/Writer.hs b/pandoc-lua-engine/test/Tests/Lua/Writer.hs
index c9a0d478c..97d772bc5 100644
--- a/pandoc-lua-engine/test/Tests/Lua/Writer.hs
+++ b/pandoc-lua-engine/test/Tests/Lua/Writer.hs
@@ -11,6 +11,7 @@ Tests for custom Lua writers.
 module Tests.Lua.Writer (tests) where
 
 import Data.Default (Default (def))
+import Data.Maybe (fromMaybe)
 import Text.Pandoc.Class (runIOorExplode, readFileStrict)
 import Text.Pandoc.Extensions (Extension (..))
 import Text.Pandoc.Format (ExtensionsDiff (..), FlavoredFormat (..),
@@ -59,13 +60,8 @@ tests =
   , goldenVsString "template"
     "writer-template.out.txt"
     (runIOorExplode $ do
-        txt <- writeCustom "writer-template.lua" >>= \case
-          (TextWriter f, _, mt) -> do
-            template <- mt
-            let opts = def{ writerTemplate = Just template }
-            f opts (B.doc (B.plain (B.str "body goes here")))
-          _ -> error "Expected a text writer"
-        pure $ BL.fromStrict (UTF8.fromText txt))
+        (_, _, template) <- writeCustom "writer-template.lua"
+        pure . BL.fromStrict . UTF8.fromText $ fromMaybe "" template)
 
   , testCase "preset extensions" $ do
       let ediff = ExtensionsDiff{extsToEnable = [], extsToDisable = []}
diff --git a/pandoc-lua-engine/test/writer-template.lua b/pandoc-lua-engine/test/writer-template.lua
index c90f7c1ef..8908c0ebb 100644
--- a/pandoc-lua-engine/test/writer-template.lua
+++ b/pandoc-lua-engine/test/writer-template.lua
@@ -3,5 +3,5 @@ function Writer (doc, opts)
 end
 
 function Template ()
-  return pandoc.template.compile '<!-- start -->\n$body$\n<!-- stop -->\n'
+  return '<!-- start -->\n$body$\n<!-- stop -->\n'
 end
diff --git a/pandoc-lua-engine/test/writer-template.out.txt b/pandoc-lua-engine/test/writer-template.out.txt
index 1fb343c28..18e531cff 100644
--- a/pandoc-lua-engine/test/writer-template.out.txt
+++ b/pandoc-lua-engine/test/writer-template.out.txt
@@ -1,4 +1,3 @@
 <!-- start -->
-body goes here
-
+$body$
 <!-- stop -->
diff --git a/src/Text/Pandoc/App/CommandLineOptions.hs b/src/Text/Pandoc/App/CommandLineOptions.hs
index 78f548fb3..a65fe5a04 100644
--- a/src/Text/Pandoc/App/CommandLineOptions.hs
+++ b/src/Text/Pandoc/App/CommandLineOptions.hs
@@ -51,6 +51,7 @@ import Text.Pandoc.App.Opt (Opt (..), LineEnding (..), IpynbOutput (..),
                             fullDefaultsPath, OptInfo(..))
 import Text.Pandoc.Filter (Filter (..))
 import Text.Pandoc.Highlighting (highlightingStyles, lookupHighlightingStyle)
+import Text.Pandoc.Scripting (ScriptingEngine (..))
 import Text.Pandoc.Shared (safeStrRead)
 import Text.Printf
 import qualified Control.Exception as E
@@ -60,7 +61,6 @@ import qualified Data.ByteString.Lazy as B
 import qualified Data.Map as M
 import qualified Data.Text as T
 import qualified Text.Pandoc.UTF8 as UTF8
-import Text.Pandoc.Scripting (ScriptingEngine(..))
 
 parseOptions :: [OptDescr (Opt -> ExceptT OptInfo IO Opt)]
              -> Opt -> IO (Either OptInfo Opt)
@@ -105,7 +105,7 @@ parseOptionsFromArgs options' defaults prg rawArgs = do
 -- | React to an 'OptInfo' by printing the requested information
 -- and exiting or (if there was a parsing error) raising an error.
 handleOptInfo :: ScriptingEngine -> OptInfo -> IO ()
-handleOptInfo _engine info = E.handle (handleError . Left) $ do
+handleOptInfo engine info = E.handle (handleError . Left) $ do
   case info of
     BashCompletion -> do
       datafiles <- getDataFileNames
@@ -152,9 +152,19 @@ handleOptInfo _engine info = E.handle (handleError . Left) $ do
       mapM_ (UTF8.hPutStrLn stdout . fst) highlightingStyles
     PrintDefaultTemplate mbout fmt -> do
       let write = maybe (UTF8.hPutStr stdout) (UTF8.writeFile) mbout
-      templ <- runIO $ do
-                 setUserDataDir Nothing
-                 getDefaultTemplate fmt
+
+      templ <- runIO $
+               case splitExtension (T.unpack fmt) of
+                    (_, "") -> do
+                      -- built-in format
+                      setUserDataDir Nothing
+                      getDefaultTemplate fmt
+                    _ -> do
+                      -- format looks like a filepath => custom writer
+                      (_, _, mt) <- engineWriteCustom engine (T.unpack fmt)
+                      case mt of
+                        Just t  -> pure t
+                        Nothing -> E.throw $ PandocNoTemplateError fmt
       case templ of
            Right t
              | T.null t -> -- e.g. for docx, odt, json:
diff --git a/src/Text/Pandoc/App/OutputSettings.hs b/src/Text/Pandoc/App/OutputSettings.hs
index 8b5d450cf..c3f0ade8b 100644
--- a/src/Text/Pandoc/App/OutputSettings.hs
+++ b/src/Text/Pandoc/App/OutputSettings.hs
@@ -107,6 +107,9 @@ optToOutputSettings scriptingEngine opts = do
     Format.parseFlavoredFormat writerName
 
   let standalone = optStandalone opts || not (isTextFormat format) || pdfOutput
+  let templateOrThrow = \case
+        Left  e -> throwError $ PandocTemplateError (T.pack e)
+        Right t -> pure t
   let processCustomTemplate getDefault =
         case optTemplate opts of
           _ | not standalone -> return Nothing
@@ -118,16 +121,18 @@ optToOutputSettings scriptingEngine opts = do
                         _  -> tp
             getTemplate tp'
               >>= runWithPartials . compileTemplate tp'
-              >>= (\case
-                      Left  e -> throwError $ PandocTemplateError (T.pack e)
-                      Right t -> return $ Just t)
+              >>= fmap Just . templateOrThrow
 
   (writer, writerExts, mtemplate) <-
     if "lua" `T.isSuffixOf` format
     then do
-      (w, extsConf, mt) <- engineWriteCustom scriptingEngine (T.unpack format)
+      let path = T.unpack format
+      (w, extsConf, mt) <- engineWriteCustom scriptingEngine path
       wexts <- Format.applyExtensionsDiff extsConf flvrd
-      templ <- processCustomTemplate mt
+      templ <- processCustomTemplate $ case mt of
+        Nothing -> throwError $ PandocNoTemplateError format
+        Just t  -> (runWithDefaultPartials $ compileTemplate path t) >>=
+                   templateOrThrow
       return (w, wexts, templ)
     else do
       tmpl <- processCustomTemplate (compileDefaultTemplate format)
diff --git a/src/Text/Pandoc/Error.hs b/src/Text/Pandoc/Error.hs
index 434b37240..915fa04cb 100644
--- a/src/Text/Pandoc/Error.hs
+++ b/src/Text/Pandoc/Error.hs
@@ -52,6 +52,7 @@ data PandocError = PandocIOError Text IOError
                  | PandocCouldNotFindMetadataFileError Text
                  | PandocResourceNotFound Text
                  | PandocTemplateError Text
+                 | PandocNoTemplateError Text
                  | PandocAppError Text
                  | PandocEpubSubdirectoryError Text
                  | PandocMacroLoop Text
@@ -100,6 +101,7 @@ renderError e =
     PandocResourceNotFound fn ->
         "File " <> fn <> " not found in resource path"
     PandocTemplateError s -> "Error compiling template " <> s
+    PandocNoTemplateError fp -> "No template defined in " <> fp
     PandocAppError s -> s
     PandocEpubSubdirectoryError s ->
       "EPUB subdirectory name '" <> s <> "' contains illegal characters"
@@ -174,6 +176,7 @@ handleError (Left e) =
       PandocSyntaxMapError{} -> 67
       PandocFilterError{} -> 83
       PandocLuaError{} -> 84
+      PandocNoTemplateError{} -> 87
       PandocNoScriptingEngine -> 89
       PandocMacroLoop{} -> 91
       PandocUTF8DecodingError{} -> 92
diff --git a/src/Text/Pandoc/Scripting.hs b/src/Text/Pandoc/Scripting.hs
index 29027dd6d..1942014cb 100644
--- a/src/Text/Pandoc/Scripting.hs
+++ b/src/Text/Pandoc/Scripting.hs
@@ -23,7 +23,6 @@ import Text.Pandoc.Definition (Pandoc)
 import Text.Pandoc.Error (PandocError (PandocNoScriptingEngine))
 import Text.Pandoc.Filter.Environment (Environment)
 import Text.Pandoc.Format (ExtensionsConfig)
-import Text.Pandoc.Templates (Template)
 import Text.Pandoc.Readers (Reader)
 import Text.Pandoc.Writers (Writer)
 
@@ -42,7 +41,7 @@ data ScriptingEngine = ScriptingEngine
 
   , engineWriteCustom :: forall m. (PandocMonad m, MonadIO m)
                       => FilePath
-                      -> m (Writer m, ExtensionsConfig, m (Template Text))
+                      -> m (Writer m, ExtensionsConfig, Maybe Text)
     -- ^ Invoke the given script file to convert to any custom format.
   }