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.

3 files changed, 5 insertions, 10 deletions

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 -->