diff -r 5857be01962e -r 8243e999f22b mercurial/dispatch.py
--- a/mercurial/dispatch.py	Thu Jun 25 17:44:15 2015 -0500
+++ b/mercurial/dispatch.py	Thu Jun 25 17:45:49 2015 -0500
@@ -129,10 +129,11 @@
                 for sec, name, val in cfgs:
                     req.repo.ui.setconfig(sec, name, val, source='--config')
 
-            # if we are in HGPLAIN mode, then disable custom debugging
+            # developer config: ui.debugger
             debugger = ui.config("ui", "debugger")
             debugmod = pdb
             if not debugger or ui.plain():
+                # if we are in HGPLAIN mode, then disable custom debugging
                 debugger = 'pdb'
             elif '--debugger' in req.args:
                 # This import can be slow for fancy debuggers, so only