Compare plain list type in diff.rs.

src/compare/util.rs

@@ -190,3 +190,15 @@ pub(crate) fn get_property<'s, 'x>(
     };
     Ok(Some(*prop))
 }
+
+/// Get a named property containing an unquoted atom from the emacs token.
+///
+/// Returns None if key is not found.
+pub(crate) fn get_property_unquoted_atom<'s, 'x>(
+    emacs: &'s Token<'s>,
+    key: &'x str,
+) -> Result<Option<&'s str>, Box<dyn std::error::Error>> {
+    Ok(get_property(emacs, key)?
+        .map(Token::as_atom)
+        .map_or(Ok(None), |r| r.map(Some))?)
+}