Lua: add function pandoc.format.extensions.

This simplifies the creation of custom readers and writers that are
based on built-in formats.

doc/lua-filters.md

@@ -4441,6 +4441,27 @@ Returns:
 
 -   default extensions enabled for `format` (FormatExtensions)
 
+### extensions {#pandoc.format.extensions}
+
+Returns the extension configuration for the given format.
+The configuration is represented as a table with all supported
+extensions as keys and their default status as value, with
+`true` indicating that the extension is enabled by default,
+while `false` marks a supported extension that's disabled.
+
+This function can be used to assign a value to the `Extensions`
+global in custom readers and writers.
+
+Parameters:
+
+`format`
+:   format identifier (string)
+
+Returns:
+
+-  extensions config
+
+
 # Module pandoc.path
 
 Module for file path manipulations.

pandoc-lua-engine/src/Text/Pandoc/Lua/Marshal/Format.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE LambdaCase           #-}
 {-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE TupleSections        #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {- |
    Module      : Text.Pandoc.Lua.Marshaling.Format
@@ -14,6 +15,7 @@ module Text.Pandoc.Lua.Marshal.Format
   ( peekExtensions
   , pushExtensions
   , peekExtensionsConfig
+  , pushExtensionsConfig
   , peekFlavoredFormat
   ) where
 
@@ -23,20 +25,25 @@ import Data.Maybe (fromMaybe)
 import HsLua
 import Text.Pandoc.Error (PandocError (..))
 import Text.Pandoc.Extensions
-  ( Extension, Extensions, extensionsFromList
-  , getDefaultExtensions, readExtension )
+  ( Extension, Extensions, extensionsFromList, extensionsToList
+  , getDefaultExtensions, readExtension, showExtension )
 import Text.Pandoc.Format
   ( ExtensionsConfig (..), ExtensionsDiff (..), FlavoredFormat (..)
   , diffExtensions, parseFlavoredFormat)
 import Text.Pandoc.Lua.PandocLua (PandocLua (unPandocLua))
 
--- | Retrieves an 'Extensions' set from the Lua stack.
+-- | Retrieves a single 'Extension' from the Lua stack.
 peekExtension :: LuaError e => Peeker e Extension
 peekExtension idx = do
   extString <- peekString idx
   return $ readExtension extString
 {-# INLINE peekExtension #-}
 
+-- | Pushes an individual 'Extension' to the Lua stack.
+pushExtension :: LuaError e => Pusher e Extension
+pushExtension = pushText . showExtension
+{-# INLINE pushExtension #-}
+
 -- | Retrieves an 'Extensions' set from the Lua stack.
 peekExtensions :: LuaError e => Peeker e Extensions
 peekExtensions = fmap extensionsFromList . peekList peekExtension
@@ -62,6 +69,14 @@ peekExtensionsConfig idx = do
     , extsSupported = extsToEnable diff <> extsToDisable diff
     }
 
+-- | Pushes an 'ExtensionsConfig' value as a table with that maps
+-- extensions to their default enabled/disabled status.
+pushExtensionsConfig :: LuaError e => Pusher e ExtensionsConfig
+pushExtensionsConfig (ExtensionsConfig def supported) =
+  pushKeyValuePairs pushExtension pushBool $
+    map (,False) (extensionsToList supported) ++
+    map (,True)  (extensionsToList def)
+
 instance Peekable ExtensionsConfig where
   safepeek = peekExtensionsConfig
 

pandoc-lua-engine/src/Text/Pandoc/Lua/Module/Format.hs

@@ -14,7 +14,8 @@ module Text.Pandoc.Lua.Module.Format
 import HsLua
 import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Extensions (getAllExtensions, getDefaultExtensions)
-import Text.Pandoc.Lua.Marshal.Format (pushExtensions)
+import Text.Pandoc.Format (getExtensionsConfig)
+import Text.Pandoc.Lua.Marshal.Format (pushExtensions, pushExtensionsConfig)
 import Text.Pandoc.Lua.PandocLua ()
 
 import qualified Data.Text as T
@@ -56,4 +57,19 @@ functions =
         , "can have an effect when reading a format but not when"
         , "writing it, or *vice versa*."
         ]
+
+  , defun "extensions"
+     ### liftPure getExtensionsConfig
+     <#> textParam "format" "format identifier"
+     =#> functionResult pushExtensionsConfig "table" "extensions config"
+     #? T.unlines
+        [ "Returns the extension configuration for the given format."
+        , "The configuration is represented as a table with all supported"
+        , "extensions as keys and their default status as value, with"
+        , "`true` indicating that the extension is enabled by default,"
+        , "while `false` marks a supported extension that's disabled."
+        , ""
+        , "This function can be used to assign a value to the `Extensions`"
+        , "global in custom readers and writers."
+        ]
   ]

pandoc-lua-engine/test/lua/module/pandoc-format.lua

@@ -31,4 +31,20 @@ return {
       assert.are_same(format.all_extensions('docx'), docx_default_exts)
     end),
   },
+
+  group 'extensions' {
+    test('org', function ()
+      local org_default_exts = {
+        ascii_identifiers = false,
+        auto_identifiers = true,
+        citations = true,
+        east_asian_line_breaks = false,
+        fancy_lists = false,
+        gfm_auto_identifiers = false,
+        smart = false,
+        task_lists = true,
+      }
+      assert.are_same(format.extensions 'org', org_default_exts)
+    end),
+  },
 }