Lua: include lpeg module

Compiles the 'lpeg' library (Parsing Expression Grammars For Lua) into
the program.

Package maintainers may choose to rely on package dependencies to make
lpeg available, in which case they can compile the with the constraint
`lpeg +rely-on-shared-lpeg-library`.

pandoc.cabal

@@ -561,6 +561,7 @@ 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,
                  mtl                   >= 2.2      && < 2.3,
                  network               >= 2.6,
                  network-uri           >= 2.6      && < 2.8,

src/Text/Pandoc/Lua/Packages.hs

@@ -22,6 +22,7 @@ import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua, loadDefaultModule)
 import qualified HsLua as Lua
 import qualified HsLua.Module.Path as Path
 import qualified HsLua.Module.Text as Text
+import qualified Lua.LPeg as LPeg
 import qualified Text.Pandoc.Lua.Module.Pandoc as Pandoc
 import qualified Text.Pandoc.Lua.Module.MediaBag as MediaBag
 import qualified Text.Pandoc.Lua.Module.System as System
@@ -35,6 +36,9 @@ installPandocPackageSearcher = liftPandocLua $ do
   shiftArray
   Lua.pushHaskellFunction $ Lua.toHaskellFunction pandocPackageSearcher
   Lua.rawseti (Lua.nth 2) 1
+  -- add lpeg searcher as last searcher
+  Lua.pushHaskellFunction $ Lua.state >>= Lua.liftIO . LPeg.lpeg_searcher
+  Lua.rawseti (Lua.nth 2) 6
   Lua.pop 1           -- remove 'package.searchers' from stack
  where
   shiftArray = forM_ [4, 3, 2, 1] $ \i -> do
@@ -64,5 +68,5 @@ pandocPackageSearcher pkgName =
     Lua.pushHaskellFunction f
     return 1
   reportPandocSearcherFailure = liftPandocLua $ do
-    Lua.push ("\n\t" <> pkgName <> "is not one of pandoc's default packages")
+    Lua.push ("\n\t" <> pkgName <> " is not one of pandoc's default packages")
     return (Lua.NumResults 1)

stack.yaml

@@ -12,6 +12,7 @@ extra-deps:
 - doctemplates-0.10
 - emojis-0.1.2
 - doclayout-0.3.1.1
+- lpeg-1.0.0
 - hslua-2.0.0
 - hslua-classes-2.0.0
 - hslua-core-2.0.0