--- a/hgext3rd/topic/__init__.py	Thu Jul 06 03:56:36 2017 +0530
+++ b/hgext3rd/topic/__init__.py	Thu Jul 06 03:31:11 2017 +0530
@@ -232,6 +232,11 @@
                 current = self.currenttopic
                 if current:
                     ctx.extra()[constants.extrakey] = current
+                else:
+                    if ui.configbool('experimental', 'enforce-topic', False):
+                        # calling a function to raise an error as error variable
+                        # in this function does not refer to the error module
+                        panicforuntopicedcommit()
             if (isinstance(ctx, context.memctx) and
                 ctx.extra().get('amend_source') and
                 ctx.topic() and
@@ -489,6 +494,12 @@
         fm.plain('\n')
     fm.end()
 
+def panicforuntopicedcommit():
+    msg = _("no active topic")
+    hint = _("set a current topic or use '--config " +
+             "experimental.enforce-topic=no' to commit without a topic")
+    raise error.Abort(msg, hint=hint)
+
 def summaryhook(ui, repo):
     t = repo.currenttopic
     if not t: