RST reader: improve support for custom roles

- Add "sourceCode" to classes for :code: role, and anything inheriting
  from it.
- Add the name of the custom role to classes if the Inline constructor
  supports Attr.
- If the custom role directive does not specify a parent role, inherit
  from the :span: role.

This differs somewhat from the rst2xml.py behavior.  If a custom role
inherits from another custom role, Pandoc will attach both roles' names
as classes.  rst2xml.py will only use the class of the directly invoked
role (though in the case of inheriting from a :code: role with a
:language: defined, it will also provide the inherited language as a
class).

src/Text/Pandoc/Readers/RST.hs

@@ -39,11 +39,11 @@ import Text.Pandoc.Parsing
 import Text.Pandoc.Options
 import Control.Monad ( when, liftM, guard, mzero, mplus )
 import Data.List ( findIndex, intersperse, intercalate,
-                   transpose, sort, deleteFirstsBy, isSuffixOf )
+                   transpose, sort, deleteFirstsBy, isSuffixOf , nub, union)
 import Data.Maybe (fromMaybe)
 import qualified Data.Map as M
 import Text.Printf ( printf )
-import Control.Applicative ((<$>), (<$), (<*), (*>), (<*>))
+import Control.Applicative ((<$>), (<$), (<*), (*>), (<*>), pure)
 import Text.Pandoc.Builder (Inlines, Blocks, trimInlines, (<>))
 import qualified Text.Pandoc.Builder as B
 import Data.Monoid (mconcat, mempty)
@@ -619,7 +619,6 @@ directive' = do
 
 -- TODO:
 --  - Silently ignores illegal fields
---  - Silently drops classes
 --  - Only supports :format: fields with a single format for :raw: roles,
 --    change Text.Pandoc.Definition.Format to fix
 addNewRole :: String -> [(String, String)] -> RSTParser Blocks
@@ -631,7 +630,7 @@ addNewRole roleString fields = do
         Nothing -> return parentRole
 
     let fmt = if baseRole == "raw" then lookup "format" fields else Nothing
-        annotate = maybe id addLanguage $
+        annotate = maybe (addClass role) (addLanguage role) $
             if baseRole == "code"
                then lookup "language" fields
                else Nothing
@@ -643,10 +642,10 @@ addNewRole roleString fields = do
 
     return $ B.singleton Null
   where
-    addLanguage lang (ident, classes, keyValues) =
-        (ident, "sourceCode" : lang : classes, keyValues)
+    addLanguage role lang (ident, classes, keyValues) =
+        (ident, nub ("sourceCode" : lang : role : classes), keyValues)
     inheritedRole =
-        (,) <$> roleNameEndingIn (char '(') <*> roleNameEndingIn (char ')')
+        (,) <$> roleName <*> ((char '(' *> roleName <* char ')') <|> pure "span")
 
 -- Can contain character codes as decimal numbers or
 -- hexadecimal numbers, prefixed by 0x, x, \x, U+, u, or \u
@@ -1011,7 +1010,8 @@ renderRole contents fmt role attr = case role of
     "title-reference" -> titleRef contents
     "title" -> titleRef contents
     "t" -> titleRef contents
-    "code" -> return $ B.codeWith (union attr ["code"]) contents
+    "code" -> return $ B.codeWith (addClass "sourceCode" attr) contents
+    "span" -> return $ B.spanWith attr $ B.str contents
     "raw" -> return $ B.rawInline (fromMaybe "" fmt) contents
     custom -> do
         customRole <- stateRstCustomRoles <$> getState
@@ -1032,11 +1032,14 @@ renderRole contents fmt role attr = case role of
      where padNo = replicate (4 - length pepNo) '0' ++ pepNo
            pepUrl = "http://www.python.org/dev/peps/pep-" ++ padNo ++ "/"
 
-roleNameEndingIn :: RSTParser Char -> RSTParser String
-roleNameEndingIn end = many1Till (letter <|> char '-') end
+addClass :: String -> Attr -> Attr
+addClass c (ident, classes, keyValues) = (ident, union classes [c], keyValues)
+
+roleName :: RSTParser String
+roleName = many1 (letter <|> char '-')
 
 roleMarker :: RSTParser String
-roleMarker = char ':' *> roleNameEndingIn (char ':')
+roleMarker = char ':' *> roleName <* char ':'
 
 roleBefore :: RSTParser (String,String)
 roleBefore = try $ do