Allow specifying string value in metadata using `!!literal` tag.

This is experimental.  Normally metadata values are interpreted
as markdown, but if the !!literal tag is used they will be interpreted
as plain strings.

We need to consider whether this can still be implemented if
we switch back from HsYAML to yaml for performance reasons.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/Text/Pandoc/Readers/Metadata.hs b/src/Text/Pandoc/Readers/Metadata.hs
index 23ceb40f9..d91c4a406 100644
--- a/src/Text/Pandoc/Readers/Metadata.hs
+++ b/src/Text/Pandoc/Readers/Metadata.hs
@@ -99,10 +99,12 @@ yamlToMetaValue pBlocks (YAML.Scalar _ x) =
        YAML.SBool b      -> return $ return $ MetaBool b
        YAML.SFloat d     -> return $ return $ MetaString $ tshow d
        YAML.SInt i       -> return $ return $ MetaString $ tshow i
-       YAML.SUnknown _ t ->
-         case checkBoolean t of
-           Just b        -> return $ return $ MetaBool b
-           Nothing       -> toMetaValue pBlocks t
+       YAML.SUnknown tag t
+         | (T.takeWhileEnd (/= ':') <$> YE.tagToText tag) ==
+           Just "literal" -> return $ return $ MetaString t
+         | otherwise -> case checkBoolean t of
+                           Just b    -> return $ return $ MetaBool b
+                           Nothing   -> toMetaValue pBlocks t
        YAML.SNull        -> return $ return $ MetaString ""
 
 yamlToMetaValue pBlocks (YAML.Sequence _ _ xs) = do