Lua: fix regression in package searcher

This caused `require 'module'` to fail for third party packages.

Fixes: #6361

src/Text/Pandoc/Lua/Packages.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {- |
    Module      : Text.Pandoc.Lua.Packages
@@ -14,9 +15,11 @@ module Text.Pandoc.Lua.Packages
   ( installPandocPackageSearcher
   ) where
 
+import Control.Monad.Catch (try)
 import Control.Monad (forM_)
 import Data.ByteString (ByteString)
 import Foreign.Lua (Lua, NumResults)
+import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Class.PandocMonad (readDataFile)
 import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua)
 
@@ -58,8 +61,11 @@ pandocPackageSearcher pkgName =
     return 1
   searchPureLuaLoader = do
     let filename = pkgName ++ ".lua"
-    script <- readDataFile filename
-    pushWrappedHsFun (loadStringAsPackage pkgName script)
+    try (readDataFile filename) >>= \case
+      Right script -> pushWrappedHsFun (loadStringAsPackage pkgName script)
+      Left (_ :: PandocError) -> liftPandocLua $ do
+        Lua.push ("\n\tno file '" ++ filename ++ "' in pandoc's datadir")
+        return (1 :: NumResults)
 
 loadStringAsPackage :: String -> ByteString -> Lua NumResults
 loadStringAsPackage pkgName script = do

test/Tests/Lua.hs

@@ -172,6 +172,12 @@ tests = map (localOption (QuickCheckTests 20))
       Lua.liftIO . assertEqual "pandoc-types version is wrong" pandocTypesVersion
         =<< Lua.peek Lua.stackTop
 
+  , testCase "require file" $
+    assertFilterConversion "requiring file failed"
+      "require-file.lua"
+      (doc $ para "ignored")
+      (doc $ para (str . T.pack $ "lua" </> "require-file.lua"))
+
   , testCase "Allow singleton inline in constructors" . runLuaTest $ do
       Lua.liftIO . assertEqual "Not the exptected Emph" (Emph [Str "test"])
         =<< Lua.callFunc "pandoc.Emph" (Str "test")

test/lua/require-file.lua

@@ -0,0 +1,2 @@
+package.path = package.path .. ';lua/?.lua'
+require 'script-name'