--- a/hgext3rd/topic/__init__.py	Tue May 03 21:46:23 2022 +0400
+++ b/hgext3rd/topic/__init__.py	Tue May 03 21:45:59 2022 +0400
@@ -504,6 +504,24 @@
             return super(topicrepo, self).commitctx(ctx, *args, **kwargs)
 
         @util.propertycache
+        def _tnscache(self):
+            return {}
+
+        @property
+        def topic_namespaces(self):
+            if self._topic_namespaces is not None:
+                return self._topic_namespaces
+            namespaces = set([self.currenttns])
+            for c in self.set(b'not public()'):
+                namespaces.add(c.topic_namespace())
+            self._topic_namespaces = namespaces
+            return namespaces
+
+        @property
+        def currenttns(self):
+            return self.vfs.tryread(b'topic-namespace') or b'default'
+
+        @util.propertycache
         def _topiccache(self):
             return {}
 
@@ -545,6 +563,7 @@
         def invalidatevolatilesets(self):
             # XXX we might be able to move this to something invalidated less often
             super(topicrepo, self).invalidatevolatilesets()
+            self._topic_namespaces = None
             self._topics = None
 
         def peer(self):
@@ -691,6 +710,7 @@
             return tr
 
     repo.__class__ = topicrepo
+    repo._topic_namespaces = None
     repo._topics = None
     if util.safehasattr(repo, 'names'):
         repo.names.addnamespace(namespaces.namespace(
@@ -1501,6 +1521,12 @@
     if topic:
         _changecurrenttopic(repo, topic)
 
+@command(b'debug-topic-namespaces', [])
+def debugtopicnamespaces(ui, repo, **opts):
+    """list repository namespaces"""
+    for tns in repo.topic_namespaces:
+        ui.write(b'%s\n' % (tns,))
+
 @command(b'debug-parse-fqbn', commands.formatteropts, _(b'FQBN'), optionalrepo=True)
 def debugparsefqbn(ui, repo, fqbn, **opts):
     """parse branch//namespace/topic string into its components"""