Lua: use proper interface functions to access the CommonState.

- The `PANDOC_STATE` is no longer a userdata object, but a table that
  behaves like the old object.

- Log messages in `PANDOC_STATE.log` are now in temporal order.

9 files changed, 79 insertions, 82 deletions

diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Global.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Global.hs
index 079181d74..d9902df98 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Global.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Global.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase         #-}
 {-# LANGUAGE OverloadedStrings  #-}
 {- |
    Module      : Text.Pandoc.Lua
@@ -16,14 +17,18 @@ module Text.Pandoc.Lua.Global
 
 import HsLua as Lua
 import HsLua.Module.Version (pushVersion)
-import Text.Pandoc.Class (CommonState)
+import Text.Pandoc.Class ( getInputFiles, getOutputFile, getLog
+                         , getRequestHeaders, getResourcePath, getSourceURL
+                         , getUserDataDir, getTrace, getVerbosity
+                         )
 import Text.Pandoc.Definition (Pandoc, pandocTypesVersion)
 import Text.Pandoc.Error (PandocError)
-import Text.Pandoc.Lua.Marshal.CommonState (pushCommonState)
+import Text.Pandoc.Lua.Marshal.List (pushPandocList)
+import Text.Pandoc.Lua.Marshal.LogMessage (pushLogMessage)
 import Text.Pandoc.Lua.Marshal.Pandoc (pushPandoc)
 import Text.Pandoc.Lua.Marshal.ReaderOptions (pushReaderOptionsReadonly)
 import Text.Pandoc.Lua.Marshal.WriterOptions (pushWriterOptions)
-import Text.Pandoc.Lua.PandocLua ()
+import Text.Pandoc.Lua.PandocLua (unPandocLua)
 import Text.Pandoc.Options (ReaderOptions, WriterOptions)
 import Text.Pandoc.Version (pandocVersion)
 
@@ -37,7 +42,7 @@ data Global =
   | PANDOC_READER_OPTIONS ReaderOptions
   | PANDOC_WRITER_OPTIONS WriterOptions
   | PANDOC_SCRIPT_FILE FilePath
-  | PANDOC_STATE CommonState
+  | PANDOC_STATE
   | PANDOC_VERSION
   -- Cannot derive instance of Data because of CommonState
 
@@ -66,8 +71,47 @@ setGlobal global = case global of
   PANDOC_SCRIPT_FILE filePath -> do
     Lua.pushString filePath
     Lua.setglobal "PANDOC_SCRIPT_FILE"
-  PANDOC_STATE commonState -> do
-    pushCommonState commonState
+  PANDOC_STATE -> do
+    -- The common state is an opaque value. We provide a table that
+    -- contains the values accessible through the PandocMonad API. This
+    -- is for backwards compatibility, as the state used to be exposed
+    -- as a read-only object.
+    Lua.newtable
+    Lua.newmetatable "CommonStateInterface"
+    Lua.pushHaskellFunction $ do
+      Lua.forcePeek (peekText (Lua.nthBottom 2)) >>= \case
+        "input_files" -> do
+          pushPandocList pushString =<< unPandocLua getInputFiles
+          return 1
+        "output_file" -> do
+          maybe pushnil pushString =<< unPandocLua getOutputFile
+          return 1
+        "log" -> do
+          pushPandocList pushLogMessage =<< unPandocLua getLog
+          return 1
+        "request_headers" -> do
+          pushPandocList (pushPair pushText pushText)
+                   =<< unPandocLua getRequestHeaders
+          return 1
+        "resource_path" -> do
+          pushPandocList pushString =<< unPandocLua getResourcePath
+          return 1
+        "source_url" -> do
+          maybe pushnil pushText =<< unPandocLua getSourceURL
+          return 1
+        "user_data_dir" -> do
+          maybe pushnil pushString =<< unPandocLua getUserDataDir
+          return 1
+        "trace" -> do
+          pushBool =<< unPandocLua getTrace
+          return 1
+        "verbosity" -> do
+          pushString . show =<< unPandocLua getVerbosity
+          return 1
+        _ ->
+          failLua "Unknown key"
+    Lua.setfield (Lua.nth 2) "__index"
+    Lua.setmetatable (Lua.nth 2)
     Lua.setglobal "PANDOC_STATE"
   PANDOC_VERSION              -> do
     pushVersion pandocVersion
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/CommonState.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/CommonState.hs
index b0d2b0990..3f705616d 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/CommonState.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/CommonState.hs
@@ -16,41 +16,15 @@ module Text.Pandoc.Lua.Marshal.CommonState
   ) where
 
 import HsLua
-import Text.Pandoc.Class (CommonState (..))
-import Text.Pandoc.Lua.Marshal.List (pushPandocList)
-import Text.Pandoc.Lua.Marshal.LogMessage (pushLogMessage)
+import Text.Pandoc.Class (CommonState)
 
 -- | Lua type used for the @CommonState@ object.
+--
+-- This is an opaque value that is required for the Lua interpreter
+-- to become an instance of "PandocMonad".
+--
 typeCommonState :: LuaError e => DocumentedType e CommonState
-typeCommonState = deftype "CommonState" []
-  [ readonly "input_files" "input files passed to pandoc"
-      (pushPandocList pushString, stInputFiles)
-
-  , readonly "output_file" "the file to which pandoc will write"
-      (maybe pushnil pushString, stOutputFile)
-
-  , readonly "log" "list of log messages"
-      (pushPandocList pushLogMessage, stLog)
-
-  , readonly "request_headers" "headers to add for HTTP requests"
-      (pushPandocList (pushPair pushText pushText), stRequestHeaders)
-
-  , readonly "resource_path"
-      "path to search for resources like included images"
-      (pushPandocList pushString, stResourcePath)
-
-  , readonly "source_url" "absolute URL + dir of 1st source file"
-      (maybe pushnil pushText, stSourceURL)
-
-  , readonly "user_data_dir" "directory to search for data files"
-      (maybe pushnil pushString, stUserDataDir)
-
-  , readonly "trace" "controls whether tracing messages are issued"
-      (pushBool, stTrace)
-
-  , readonly "verbosity" "verbosity level"
-      (pushString . show, stVerbosity)
-  ]
+typeCommonState = deftype "CommonState" [] []
 
 peekCommonState :: LuaError e => Peeker e CommonState
 peekCommonState = peekUD typeCommonState
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Log.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Log.hs
index 135591981..b885cae74 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Log.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Log.hs
@@ -14,14 +14,9 @@ module Text.Pandoc.Lua.Module.Log
 
 import Data.Version (makeVersion)
 import HsLua
-import Text.Pandoc.Class
-  ( CommonState (stVerbosity, stLog)
-  , PandocMonad (putCommonState, getCommonState)
-  , report )
+import Text.Pandoc.Class (report, runSilently)
 import Text.Pandoc.Error (PandocError)
-import Text.Pandoc.Logging
-  ( Verbosity (ERROR)
-  , LogMessage (ScriptingInfo, ScriptingWarning) )
+import Text.Pandoc.Logging (LogMessage (ScriptingInfo, ScriptingWarning))
 import Text.Pandoc.Lua.Marshal.List (pushPandocList)
 import Text.Pandoc.Lua.Marshal.LogMessage (pushLogMessage)
 import Text.Pandoc.Lua.PandocLua (liftPandocLua, unPandocLua)
@@ -92,23 +87,12 @@ documentedModule = Module
 -- results of the function call after that.
 silence :: LuaE PandocError NumResults
 silence = unPandocLua $ do
-  -- get current log messages
-  origState <- getCommonState
-  let origLog = stLog origState
-  let origVerbosity = stVerbosity origState
-  putCommonState (origState { stLog = [], stVerbosity = ERROR })
-
   -- call function given as the first argument
-  liftPandocLua $ do
+  ((), messages) <- runSilently . liftPandocLua $ do
     nargs <- (NumArgs . subtract 1 . fromStackIndex) <$> gettop
     call @PandocError nargs multret
 
-  -- restore original log messages
-  newState <- getCommonState
-  let newLog = stLog newState
-  putCommonState (newState { stLog = origLog, stVerbosity = origVerbosity })
-
   liftPandocLua $ do
-    pushPandocList pushLogMessage newLog
+    pushPandocList pushLogMessage messages
     insert 1
     (NumResults . fromStackIndex) <$> gettop
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/MediaBag.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/MediaBag.hs
index da666779a..0e21c6340 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/MediaBag.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Module/MediaBag.hs
@@ -18,8 +18,7 @@ import Data.Version (makeVersion)
 import HsLua ( LuaE, DocumentedFunction, Module (..)
              , (<#>), (###), (=#>), (=?>), (#?), defun, functionResult
              , opt, parameter, since, stringParam, textParam)
-import Text.Pandoc.Class ( CommonState (..), fetchItem, fillMediaBag
-                         , getMediaBag, modifyCommonState, setMediaBag)
+import Text.Pandoc.Class ( fetchItem, fillMediaBag, getMediaBag, setMediaBag )
 import Text.Pandoc.Class.IO (writeMedia)
 import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Marshal.Pandoc (peekPandoc, pushPandoc)
@@ -71,8 +70,9 @@ documentedModule = Module
 -- | Delete a single item from the media bag.
 delete :: DocumentedFunction PandocError
 delete = defun "delete"
-  ### (\fp -> unPandocLua $ modifyCommonState
-              (\st -> st { stMediaBag = MB.deleteMedia fp (stMediaBag st) }))
+  ### (\fp -> unPandocLua $ do
+          mb <- getMediaBag
+          setMediaBag $ MB.deleteMedia fp mb)
   <#> stringParam "filepath"
       ("Filename of the item to deleted. The media bag will be " <>
        "left unchanged if no entry with the given filename exists.")
@@ -82,7 +82,7 @@ delete = defun "delete"
 -- | Delete all items from the media bag.
 empty :: DocumentedFunction PandocError
 empty = defun "empty"
-  ### unPandocLua (modifyCommonState (\st -> st { stMediaBag = mempty }))
+  ### unPandocLua (setMediaBag mempty)
   =#> []
   #? "Clear-out the media bag, deleting all items."
 
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/PandocLua.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/PandocLua.hs
index 242281b08..a968b30d3 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/PandocLua.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/PandocLua.hs
@@ -81,9 +81,7 @@ instance PandocMonad PandocLua where
     forcePeek $ peekCommonState Lua.top `lastly` pop 1
   putCommonState cst = PandocLua $ do
     pushCommonState cst
-    Lua.pushvalue Lua.top
     Lua.setfield registryindex "PANDOC_STATE"
-    Lua.setglobal "PANDOC_STATE"
 
   logOutput = IO.logOutput
 
diff --git a/pandoc-lua-engine/src/Text/Pandoc/Lua/Run.hs b/pandoc-lua-engine/src/Text/Pandoc/Lua/Run.hs
index f3bc6ebdd..19c2d0241 100644
--- a/pandoc-lua-engine/src/Text/Pandoc/Lua/Run.hs
+++ b/pandoc-lua-engine/src/Text/Pandoc/Lua/Run.hs
@@ -61,7 +61,7 @@ runPandocLuaWith :: (PandocMonad m, MonadIO m)
                  -> m a
 runPandocLuaWith runner pLua = do
   origState <- getCommonState
-  globals <- defaultGlobals
+  let globals = defaultGlobals
   (result, newState) <- liftIO . runner . unPandocLua $ do
     putCommonState origState
     liftPandocLua $ setGlobals globals
@@ -72,11 +72,9 @@ runPandocLuaWith runner pLua = do
   return result
 
 -- | Global variables which should always be set.
-defaultGlobals :: PandocMonad m => m [Global]
-defaultGlobals = do
-  commonState <- getCommonState
-  return
-    [ PANDOC_API_VERSION
-    , PANDOC_STATE commonState
-    , PANDOC_VERSION
-    ]
+defaultGlobals :: [Global]
+defaultGlobals =
+  [ PANDOC_API_VERSION
+  , PANDOC_STATE
+  , PANDOC_VERSION
+  ]
diff --git a/pandoc-lua-engine/test/Tests/Lua.hs b/pandoc-lua-engine/test/Tests/Lua.hs
index 990a1d039..82b815219 100644
--- a/pandoc-lua-engine/test/Tests/Lua.hs
+++ b/pandoc-lua-engine/test/Tests/Lua.hs
@@ -24,8 +24,7 @@ import Text.Pandoc.Builder (bulletList, definitionList, displayMath, divWith,
                             linebreak, math, orderedList, para, plain, rawBlock,
                             singleQuoted, space, str, strong,
                             HasMeta (setMeta))
-import Text.Pandoc.Class ( CommonState (stVerbosity)
-                         , modifyCommonState, runIOorExplode, setUserDataDir)
+import Text.Pandoc.Class ( runIOorExplode, setUserDataDir, setVerbosity )
 import Text.Pandoc.Definition (Attr, Block (BlockQuote, Div, Para), Pandoc,
                                Inline (Emph, Str), pandocTypesVersion)
 import Text.Pandoc.Error (PandocError (PandocLuaError))
@@ -242,7 +241,7 @@ runLuaTest :: HasCallStack => Lua.LuaE PandocError a -> IO a
 runLuaTest op = runIOorExplode $ do
   -- Disable printing of warnings on stderr: some tests will generate
   -- warnings, we don't want to see those messages.
-  modifyCommonState $ \st -> st { stVerbosity = ERROR }
+  setVerbosity ERROR
   res <- runLua $ do
     setGlobals [ PANDOC_WRITER_OPTIONS def ]
     op
diff --git a/pandoc-lua-engine/test/lua/module/globals.lua b/pandoc-lua-engine/test/lua/module/globals.lua
index 4df133e46..11b003981 100644
--- a/pandoc-lua-engine/test/lua/module/globals.lua
+++ b/pandoc-lua-engine/test/lua/module/globals.lua
@@ -110,8 +110,8 @@ return {
   },
 
   group 'PANDOC_STATE' {
-    test('is a userdata object', function ()
-      assert.are_equal(type(PANDOC_STATE), 'userdata')
+    test('is a table object', function ()
+      assert.are_equal(type(PANDOC_STATE), 'table')
     end),
     test('has property "input_files"', function ()
       assert.are_equal(type(PANDOC_STATE.input_files), 'table')
diff --git a/pandoc-lua-engine/test/lua/module/pandoc-log.lua b/pandoc-lua-engine/test/lua/module/pandoc-log.lua
index 923f03cd9..1daf6240d 100644
--- a/pandoc-lua-engine/test/lua/module/pandoc-log.lua
+++ b/pandoc-lua-engine/test/lua/module/pandoc-log.lua
@@ -22,13 +22,13 @@ return {
     end),
     test('reports a warning', function ()
       log.info('info test')
-      local msg = json.decode(json.encode(PANDOC_STATE.log[1]))
+      local msg = json.decode(json.encode(PANDOC_STATE.log:at(-1)))
       assert.are_equal(msg.message, 'info test')
       assert.are_equal(msg.type, 'ScriptingInfo')
     end),
     test('info includes the correct number', function ()
       log.info('line number test')
-      local msg = json.decode(json.encode(PANDOC_STATE.log[1]))
+      local msg = json.decode(json.encode(PANDOC_STATE.log:at(-1)))
       -- THIS NEEDS UPDATING if lines above are shifted.
       assert.are_equal(msg.line, 30)
     end),
@@ -40,7 +40,7 @@ return {
     end),
     test('reports a warning', function ()
       log.warn('testing')
-      local msg = json.decode(json.encode(PANDOC_STATE.log[1]))
+      local msg = json.decode(json.encode(PANDOC_STATE.log:at(-1)))
       assert.are_equal(msg.message, 'testing')
       assert.are_equal(msg.type, 'ScriptingWarning')
     end),