Org reader: respect unnumbered header property

Sections the `unnumbered` property should, as the name implies, be
excluded from the automatic numbering of section provided by some output
formats.  The Pandoc convention for this is to add an "unnumbered" class
to the header.  The reader treats properties as key-value pairs per
default, so a special case is added to translate the above property to a
class instead.

Closes #3095.

src/Text/Pandoc/Readers/Org/Blocks.hs

@@ -80,6 +80,10 @@ newtype PropertyValue = PropertyValue { fromValue :: String }
 toPropertyValue :: String -> PropertyValue
 toPropertyValue = PropertyValue
 
+-- | Check whether the property value is non-nil (i.e. truish).
+isNonNil :: PropertyValue -> Bool
+isNonNil p = map toLower (fromValue p) `notElem` ["()", "{}", "nil"]
+
 -- | Key/value pairs from a PROPERTIES drawer
 type Properties = [(PropertyKey, PropertyValue)]
 
@@ -200,12 +204,16 @@ propertiesToAttr properties =
     toStringPair prop = (fromKey (fst prop), fromValue (snd prop))
     customIdKey = toPropertyKey "custom_id"
     classKey    = toPropertyKey "class"
+    unnumberedKey = toPropertyKey "unnumbered"
+    specialProperties = [customIdKey, classKey, unnumberedKey]
     id'  = fromMaybe mempty . fmap fromValue . lookup customIdKey $ properties
     cls  = fromMaybe mempty . fmap fromValue . lookup classKey    $ properties
-    kvs' = map toStringPair . filter ((`notElem` [customIdKey, classKey]) . fst)
+    kvs' = map toStringPair . filter ((`notElem` specialProperties) . fst)
            $ properties
+    isUnnumbered =
+      fromMaybe False . fmap isNonNil . lookup unnumberedKey $ properties
   in
-    (id', words cls, kvs')
+    (id', words cls ++ (if isUnnumbered then ["unnumbered"] else []), kvs')
 
 tagTitle :: Inlines -> [Tag] -> Inlines
 tagTitle title tags = title <> (mconcat $ map tagToInline tags)

tests/Tests/Readers/Org.hs

@@ -818,6 +818,15 @@ tests =
                   ] =?>
           headerWith ("fubar", [], [("bar", "baz")]) 1 "foo"
 
+
+      , "Headers marked with a unnumbered property get a class of the same name" =:
+          unlines [ "* Not numbered"
+                  , "  :PROPERTIES:"
+                  , "  :UNNUMBERED: t"
+                  , "  :END:"
+                  ] =?>
+          headerWith ("not-numbered", ["unnumbered"], []) 1 "Not numbered"
+
       , "Paragraph starting with an asterisk" =:
           "*five" =?>
           para "*five"