T.P.Scripting: Refactor the scripting engine.

The new type CustomComponents is exported from T.P.Scripting, and the
ScriptEngine fields are changed. Instead of separate fields for custom
readers and writers, we now have a single function that loads any number
of "components" from a script: these may be custom readers, custom
writers, templates for writers, or extension configs. (Note: it's
possible to have a custom reader and a custom writer for a format
together in the same file.)

Pandoc now checks the folder `custom` in the user's data directory for a
matching script if it can't find one in the local directory. Previously,
the `readers` and `writers` data directories were search for custom
readers and writers, respectively. Scripts in those directories must be
moved to the `custom` folder.

Custom readers used to implement a fallback behavior that allowed to
consume just a string value as input to the `Reader` function. This has
been removed, the first argument is now always a list of sources. Use
`tostring` on that argument to get a string.

Closes #8417.

Signed-off-by: Albert Krewinkel <[email protected]>

1 files changed, 17 insertions, 11 deletions

diff --git a/src/Text/Pandoc/Scripting.hs b/src/Text/Pandoc/Scripting.hs
index 1942014cb..8b90a9749 100644
--- a/src/Text/Pandoc/Scripting.hs
+++ b/src/Text/Pandoc/Scripting.hs
@@ -11,6 +11,7 @@ Central data structure for scripting engines.
 -}
 module Text.Pandoc.Scripting
   ( ScriptingEngine (..)
+  , CustomComponents(..)
   , noEngine
   )
 where
@@ -26,6 +27,18 @@ import Text.Pandoc.Format (ExtensionsConfig)
 import Text.Pandoc.Readers (Reader)
 import Text.Pandoc.Writers (Writer)
 
+-- | A component of a custom reader/writer: a custom reader,
+-- a custom writer, a template for a custom writer, or a specification
+-- of the extensions used by a script and their default values.
+-- Note that a single script can contain all of these.
+data CustomComponents m =
+  CustomComponents
+  { customReader :: Maybe (Reader m)
+  , customWriter :: Maybe (Writer m)
+  , customTemplate :: Maybe Text
+  , customExtensions :: Maybe ExtensionsConfig
+  }
+
 -- | Structure to define a scripting engine.
 data ScriptingEngine = ScriptingEngine
   { engineName :: Text   -- ^ Name of the engine.
@@ -35,14 +48,9 @@ data ScriptingEngine = ScriptingEngine
                       -> Pandoc -> m Pandoc
     -- ^ Use the scripting engine to run a filter.
 
-  , engineReadCustom :: forall m. (PandocMonad m, MonadIO m)
-                     => FilePath -> m (Reader m, ExtensionsConfig)
-    -- ^ Function to parse input into a 'Pandoc' document.
-
-  , engineWriteCustom :: forall m. (PandocMonad m, MonadIO m)
-                      => FilePath
-                      -> m (Writer m, ExtensionsConfig, Maybe Text)
-    -- ^ Invoke the given script file to convert to any custom format.
+  , engineLoadCustom :: forall m. (PandocMonad m, MonadIO m)
+                     => FilePath -> m (CustomComponents m)
+    -- ^ Function to load a custom reader/writer from a script.
   }
 
 noEngine :: ScriptingEngine
@@ -50,8 +58,6 @@ noEngine = ScriptingEngine
   { engineName = "none"
   , engineApplyFilter = \_env _args _fp _doc ->
       throwError PandocNoScriptingEngine
-  , engineReadCustom = \_fp ->
-      throwError PandocNoScriptingEngine
-  , engineWriteCustom = \_fp ->
+  , engineLoadCustom = \_fp ->
       throwError PandocNoScriptingEngine
   }