diff -r ebe488e04ca3 -r 3741a8f86e88 mercurial/extensions.py
--- a/mercurial/extensions.py	Fri Sep 30 00:25:15 2016 +0200
+++ b/mercurial/extensions.py	Fri Sep 30 00:27:35 2016 +0200
@@ -81,6 +81,8 @@
     return mod
 
 def _reportimporterror(ui, err, failed, next):
+    # note: this ui.debug happens before --debug is processed,
+    #       Use --config ui.debug=1 to see them.
     ui.debug('could not import %s (%s): trying %s\n'
              % (failed, err, next))
     if ui.debugflag: