Add app.override_domain().

1 files changed, 8 insertions, 1 deletions

diff --git a/sphinx/application.py b/sphinx/application.py
index 7d4e3cac..860affbb 100644
--- a/sphinx/application.py
+++ b/sphinx/application.py
@@ -388,11 +388,18 @@ class Sphinx(object):
         roles.register_local_role(name, role)
 
     def add_domain(self, domain):
-        # XXX what about subclassing and overriding?
         if domain.name in self.domains:
             raise ExtensionError('domain %s already registered' % domain.name)
         self.domains[domain.name] = domain
 
+    def override_domain(self, domain):
+        if domain.name not in self.domains:
+            raise ExtensionError('domain %s not yet registered' % domain.name)
+        if not issubclass(domain, self.domains[domain.name]):
+            raise ExtensionError('new domain not a subclass of registered '
+                                 'domain' % domain.name)
+        self.domains[domain.name] = domain
+
     def add_directive_to_domain(self, domain, name, obj,
                                 content=None, arguments=None, **options):
         if domain not in self.domains: