Text.Pandoc.Lua: support Inline and Block catch-alls

Try function `Inline`/`Block` if no other filter function of the
respective type matches an element.

Closes: #3859

data/pandoc.lua

@@ -808,7 +808,8 @@ function M.global_filter()
   function is_filter_function(k)
     return M.Inline.constructor[k] or
       M.Block.constructor[k] or
-      k == "Meta" or k == "Doc" or k == "Pandoc"
+      k == "Meta" or k == "Doc" or k == "Pandoc" or
+      k == "Block" or k == "Inline"
   end
   for k, v in pairs(_G) do
     if is_filter_function(k) then

src/Text/Pandoc/Lua.hs

@@ -35,7 +35,7 @@ module Text.Pandoc.Lua (LuaException (..), pushPandocModule, runLuaFilter) where
 import Control.Monad (mplus, unless, when, (>=>))
 import Control.Monad.Trans (MonadIO (..))
 import Data.Data (DataType, Data, toConstr, showConstr, dataTypeOf,
-                  dataTypeConstrs)
+                  dataTypeConstrs, dataTypeName)
 import Data.Foldable (foldrM)
 import Data.Map (Map)
 import Data.Maybe (isJust)
@@ -108,10 +108,10 @@ constructorsFor :: DataType -> [String]
 constructorsFor x = map show (dataTypeConstrs x)
 
 inlineFilterNames :: [String]
-inlineFilterNames = constructorsFor (dataTypeOf (Str []))
+inlineFilterNames = "Inline" : constructorsFor (dataTypeOf (Str []))
 
 blockFilterNames :: [String]
-blockFilterNames = constructorsFor (dataTypeOf (Para []))
+blockFilterNames = "Block" : constructorsFor (dataTypeOf (Para []))
 
 metaFilterName :: String
 metaFilterName = "Meta"
@@ -126,10 +126,12 @@ newtype LuaFilterFunction = LuaFilterFunction { functionIndex :: Int }
 -- | Try running a filter for the given element
 tryFilter :: (Data a, FromLuaStack a, ToLuaStack a) => FunctionMap -> a -> Lua a
 tryFilter fnMap x =
-  let filterFnName = showConstr (toConstr x) in
-  case Map.lookup filterFnName fnMap of
-    Nothing -> return x
+  let filterFnName = showConstr (toConstr x)
+      catchAllName = dataTypeName (dataTypeOf x)
+  in
+  case Map.lookup filterFnName fnMap `mplus` Map.lookup catchAllName fnMap of
     Just fn -> runFilterFunction fn x
+    Nothing -> return x
 
 instance FromLuaStack LuaFilter where
   peek idx =

test/Tests/Lua.hs

@@ -70,6 +70,12 @@ tests = map (localOption (QuickCheckTests 20))
       "metatable-catch-all.lua"
       (doc . para $ "four words, three spaces")
       (doc . para $ str "7")
+
+  , testCase "Count blocks via Block-specific catch-all" $
+    assertFilterConversion "filtering with Block catch-all failed"
+      "block-count.lua"
+      (doc $ para "one" <> para "two")
+      (doc $ para "2")
   ]
 
 assertFilterConversion :: String -> FilePath -> Pandoc -> Pandoc -> Assertion

test/lua/block-count.lua

@@ -0,0 +1,11 @@
+local num_blocks = 0
+
+function Block(el)
+  num_blocks = num_blocks + 1
+end
+
+function Pandoc(blocks, meta)
+  return pandoc.Pandoc {
+    pandoc.Para{pandoc.Str(num_blocks)}
+  }
+end