Lua filter: allow filtering of meta data only

src/Text/Pandoc/Lua.hs

@@ -75,7 +75,8 @@ runAll (x:xs) = walkMWithLuaFilter x >=> runAll xs
 walkMWithLuaFilter :: LuaFilter -> Pandoc -> IO Pandoc
 walkMWithLuaFilter (LuaFilter lua fnMap) =
   walkM (execInlineLuaFilter lua fnMap) >=>
-  walkM (execBlockLuaFilter  lua fnMap)  >=>
+  walkM (execBlockLuaFilter  lua fnMap) >=>
+  walkM (execMetaLuaFilter   lua fnMap) >=>
   walkM (execDocLuaFilter    lua fnMap)
 
 type FunctionMap = Map String LuaFilterFunction
@@ -92,6 +93,17 @@ execDocLuaFilter lua fnMap x = do
     Nothing -> return x
     Just fn -> runLuaFilterFunction lua fn x
 
+execMetaLuaFilter :: LuaState
+                  -> FunctionMap
+                  -> Pandoc -> IO Pandoc
+execMetaLuaFilter lua fnMap pd@(Pandoc meta blks) = do
+  let metaFnName = "Meta"
+  case Map.lookup metaFnName fnMap of
+    Nothing -> return pd
+    Just fn -> do
+      meta' <- runLuaFilterFunction lua fn meta
+      return $ Pandoc meta' blks
+
 execBlockLuaFilter :: LuaState
                    -> FunctionMap
                    -> Block -> IO Block

test/lua/smallcaps-title.lua

@@ -0,0 +1,12 @@
+return {
+  {
+    Meta = function(meta)
+      -- The call to `MetaInlines` is redundant and used for testing purposes
+      -- only. The explicit use of a MetaValue constructor is only useful when
+      -- used with an empty table: `MetaInlines{}` is read differently than
+      -- `MetaBlocks{}`.
+      meta.title = pandoc.MetaInlines{pandoc.SmallCaps(meta.title)}
+      return meta
+    end
+  }
+}