Lua: use global state when parsing documents in pandoc.read

The function `pandoc.read` is updated to use the same state that was
used while parsing the main input files. This ensures that log messages
are preserved and that images embedded in the input are added to the
mediabag.

doc/lua-filters.md

@@ -3232,6 +3232,14 @@ Returns: the transformed inline element
 
 Parse the given string into a Pandoc document.
 
+The parser is run in the same environment that was used to read
+the main input files; it has full access to the file-system and
+the mediabag. This means that if the document specifies files to
+be included, as is possible in formats like LaTeX,
+reStructuredText, and Org, then these will be included in the
+resulting document. Any media elements are added to those
+retrieved from the other parsed input files.
+
 Parameters:
 
 `markup`:
@@ -3246,7 +3254,7 @@ Parameters:
     ReaderOptions object; defaults to the default values
     documented in the manual. ([ReaderOptions]|table)
 
-Returns: pandoc document
+Returns: pandoc document ([Pandoc](#type-pandoc))
 
 Usage:
 

src/Text/Pandoc/Lua/Module/Pandoc.hs

@@ -28,7 +28,6 @@ import Data.Proxy (Proxy (Proxy))
 import HsLua hiding (pushModule)
 import HsLua.Class.Peekable (PeekError)
 import System.Exit (ExitCode (..))
-import Text.Pandoc.Class.PandocIO (runIO)
 import Text.Pandoc.Definition
 import Text.Pandoc.Lua.Orphans ()
 import Text.Pandoc.Lua.Marshal.AST
@@ -36,7 +35,7 @@ import Text.Pandoc.Lua.Marshal.Filter (peekFilter)
 import Text.Pandoc.Lua.Marshal.ReaderOptions ( peekReaderOptions
                                              , pushReaderOptions)
 import Text.Pandoc.Lua.Module.Utils (sha1)
-import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua)
+import Text.Pandoc.Lua.PandocLua (PandocLua (unPandocLua), liftPandocLua)
 import Text.Pandoc.Options (ReaderOptions (readerExtensions))
 import Text.Pandoc.Process (pipeProcess)
 import Text.Pandoc.Readers (Reader (..), getReader)
@@ -171,13 +170,15 @@ functions =
     ### (\content mformatspec mreaderOptions -> do
             let formatSpec = fromMaybe "markdown" mformatspec
                 readerOpts = fromMaybe def mreaderOptions
-            res <- Lua.liftIO . runIO $ getReader formatSpec >>= \case
-              (TextReader r, es)      ->
-                r readerOpts{ readerExtensions = es } (UTF8.toText content)
-              (ByteStringReader r, es) ->
-                r readerOpts{ readerExtensions = es } (BSL.fromStrict content)
-            case res of
-              Right pd -> return pd -- success, got a Pandoc document
+                readAction = getReader formatSpec >>= \case
+                  (TextReader r, es)      ->
+                    r readerOpts{readerExtensions = es} (UTF8.toText content)
+                  (ByteStringReader r, es) ->
+                    r readerOpts{readerExtensions = es} (BSL.fromStrict content)
+            try (unPandocLua readAction) >>= \case
+              Right pd ->
+                -- success, got a Pandoc document
+                return pd
               Left  (PandocUnknownReaderError f) ->
                 Lua.failLua . T.unpack $ "Unknown reader: " <> f
               Left  (PandocUnsupportedExtensionError e f) ->