Lua: ensure that 're' module is always available.

The module is shipped with LPeg.

pandoc.cabal

@@ -563,7 +563,7 @@ library
                  http-types            >= 0.8      && < 0.13,
                  ipynb                 >= 0.1.0.2  && < 0.2,
                  jira-wiki-markup      >= 1.4      && < 1.5,
-                 lpeg                  >= 1.0      && < 1.1,
+                 lpeg                  >= 1.0.1    && < 1.1,
                  mtl                   >= 2.2      && < 2.3,
                  network               >= 2.6,
                  network-uri           >= 2.6      && < 2.8,

src/Text/Pandoc/Lua/Init.hs

@@ -46,6 +46,7 @@ initLuaState :: PandocLua ()
 initLuaState = do
   liftPandocLua Lua.openlibs
   installPandocPackageSearcher
+  installLpegSearcher
   initPandocModule
   requireGlobalModules
   loadInitScript "init.lua"
@@ -99,6 +100,13 @@ initLuaState = do
     -- Module on top of stack. Register as global
     Lua.setglobal "lpeg"
 
+  installLpegSearcher :: PandocLua ()
+  installLpegSearcher = liftPandocLua $ do
+    Lua.getglobal' "package.searchers"
+    Lua.pushHaskellFunction $ Lua.state >>= liftIO . LPeg.lpeg_searcher
+    Lua.rawseti (Lua.nth 2) . (+1) . fromIntegral =<< Lua.rawlen (Lua.nth 2)
+    Lua.pop 1  -- remove 'package.searchers' from stack
+
 -- | AST elements are marshaled via normal constructor functions in the
 -- @pandoc@ module. However, accessing Lua globals from Haskell is
 -- expensive (due to error handling). Accessing the Lua registry is much

test/Tests/Lua.hs

@@ -18,7 +18,7 @@ import Control.Monad (when)
 import HsLua as Lua hiding (Operation (Div), error)
 import System.FilePath ((</>))
 import Test.Tasty (TestTree, localOption)
-import Test.Tasty.HUnit (Assertion, HasCallStack, assertEqual, testCase)
+import Test.Tasty.HUnit ((@=?), Assertion, HasCallStack, assertEqual, testCase)
 import Test.Tasty.QuickCheck (QuickCheckTests (..), ioProperty, testProperty)
 import Text.Pandoc.Arbitrary ()
 import Text.Pandoc.Builder (bulletList, definitionList, displayMath, divWith,
@@ -211,6 +211,14 @@ tests = map (localOption (QuickCheckTests 20))
       ty <- Lua.ltype Lua.top
       Lua.liftIO $ assertEqual "module should be a table" Lua.TypeTable ty
 
+  , testCase "module 'lpeg' is loaded into a global" . runLuaTest $ do
+      s <- Lua.dostring "assert(type(lpeg)=='table');assert(lpeg==require'lpeg')"
+      Lua.liftIO $ Lua.OK @=? s
+
+  , testCase "module 're' is available" . runLuaTest $ do
+      s <- Lua.dostring "require 're'"
+      Lua.liftIO $ Lua.OK @=? s
+
   , testCase "informative error messages" . runLuaTest $ do
       Lua.pushboolean True
       -- Lua.newtable