diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -169,14 +169,7 @@
     except socket.error, inst:
         ui.warn(_("abort: %s\n") % inst.args[-1])
     except:
-        ui.warn(_("** unknown exception encountered,"
-                  " please report by visiting\n"))
-        ui.warn(_("**  http://mercurial.selenic.com/wiki/BugTracker\n"))
-        ui.warn(_("** Python %s\n") % sys.version.replace('\n', ''))
-        ui.warn(_("** Mercurial Distributed SCM (version %s)\n")
-               % util.version())
-        ui.warn(_("** Extensions loaded: %s\n")
-               % ", ".join([x[0] for x in extensions.extensions()]))
+        ui.exceptionheader(unknown=True)
         raise
 
     return -1
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -7,7 +7,7 @@
 
 from i18n import _
 import errno, getpass, os, socket, sys, tempfile, traceback
-import config, util, error
+import config, util, error, extensions
 
 class ui(object):
     def __init__(self, src=None):
@@ -624,3 +624,15 @@
         ui.write(ui.label(s, 'label')).
         '''
         return msg
+
+    def exceptionheader(self, unknown=False):
+        '''useful information to output before printing a traceback'''
+        if unknown:
+            self.warn(_("** unknown exception encountered,"
+                        " please report by visiting\n"))
+            self.warn(_("**  http://mercurial.selenic.com/wiki/BugTracker\n"))
+        self.warn(_("** Python %s\n") % sys.version.replace('\n', ''))
+        self.warn(_("** Mercurial Distributed SCM (version %s)\n")
+                 % util.version())
+        self.warn(_("** Extensions loaded: %s\n")
+                 % ", ".join([x[0] for x in extensions.extensions()]))