Templates: Change type of renderTemplate'.

Return value is now Text rather than being polymorphic.
This makes room for upcoming removal of the TemplateTarget
class from doctemplates.

Other code modified accordingly, and should compile with
both current and upcoming version of doctemplates.

pandoc.cabal

@@ -408,7 +408,7 @@ library
                  JuicyPixels >= 3.1.6.1 && < 3.4,
                  Glob >= 0.7 && < 0.11,
                  cmark-gfm >= 0.2 && < 0.3,
-                 doctemplates >= 0.2.1 && < 0.3,
+                 doctemplates >= 0.2.2.1 && < 0.4,
                  network-uri >= 2.6 && < 2.7,
                  network >= 2.6,
                  http-client >= 0.4.30 && < 0.7,

src/Text/Pandoc/Templates.hs

@@ -22,7 +22,7 @@ import Control.Monad.Except (throwError)
 import Data.Aeson (ToJSON (..))
 import qualified Data.Text as T
 import System.FilePath ((<.>), (</>))
-import Text.DocTemplates (Template, TemplateTarget, applyTemplate,
+import Text.DocTemplates (Template, applyTemplate,
                           compileTemplate, renderTemplate, varListToJSON)
 import Text.Pandoc.Class (PandocMonad, readDataFile)
 import Text.Pandoc.Error
@@ -57,8 +57,8 @@ getDefaultTemplate writer = do
 
 -- | Like 'applyTemplate', but runs in PandocMonad and
 -- raises an error if compilation fails.
-renderTemplate' :: (PandocMonad m, ToJSON a, TemplateTarget b)
-                => String -> a -> m b
+renderTemplate' :: (PandocMonad m, ToJSON a)
+                => String -> a -> m T.Text
 renderTemplate' template context =
   case applyTemplate (T.pack template) context of
        Left e  -> throwError (PandocTemplateError e)

src/Text/Pandoc/Writers/Custom.hs

@@ -114,7 +114,7 @@ writeCustom luaFile opts doc@(Pandoc meta _) = do
        Just tpl ->
          case applyTemplate (pack tpl) $ setField "body" body context of
               Left e  -> throw (PandocTemplateError e)
-              Right r -> return (pack r)
+              Right r -> return r
 
 docToCustom :: WriterOptions -> Pandoc -> Lua String
 docToCustom opts (Pandoc (Meta metamap) blocks) = do

src/Text/Pandoc/Writers/MediaWiki.hs

@@ -66,9 +66,9 @@ pandocToMediaWiki (Pandoc meta blocks) = do
   let main = body ++ notes
   let context = defField "body" main
                 $ defField "toc" (writerTableOfContents opts) metadata
-  pack <$> case writerTemplate opts of
-                Nothing  -> return main
-                Just tpl -> renderTemplate' tpl context
+  case writerTemplate opts of
+         Nothing  -> return $ pack main
+         Just tpl -> renderTemplate' tpl context
 
 -- | Escape special characters for MediaWiki.
 escapeString :: String -> String

src/Text/Pandoc/Writers/RTF.hs

@@ -112,13 +112,12 @@ writeRTF options doc = do
                         -- of the toc rather than a boolean:
                         . defField "toc" toc
                    else id) metadata
-  T.pack <$>
-      case writerTemplate options of
-           Just tpl -> renderTemplate' tpl context
-           Nothing  -> return $
-                       case reverse body of
-                            ('\n':_) -> body
-                            _        -> body ++ "\n"
+  case writerTemplate options of
+       Just tpl -> renderTemplate' tpl context
+       Nothing  -> return $ T.pack $
+                   case reverse body of
+                        ('\n':_) -> body
+                        _        -> body ++ "\n"
 
 -- | Convert unicode characters (> 127) into rich text format representation.
 handleUnicode :: String -> String