mercurial/extensions.py

--- a/mercurial/extensions.py	Mon Feb 15 14:57:06 2016 +0000
+++ b/mercurial/extensions.py	Wed Feb 10 16:59:34 2016 +0000
@@ -456,6 +456,10 @@
 
     return exts
 
+def notloaded():
+    '''return short names of extensions that failed to load'''
+    return [name for name, mod in _extensions.iteritems() if mod is None]
+
 def moduleversion(module):
     '''return version information from given module as a string'''
     if (util.safehasattr(module, 'getversion')