diff -r b647b923486f -r 2def402bd16d mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Thu May 25 01:45:52 2017 +0200
+++ b/mercurial/debugcommands.py	Mon May 22 11:08:52 2017 -0700
@@ -2125,6 +2125,7 @@
 def debugwalk(ui, repo, *pats, **opts):
     """show how files match on given patterns"""
     m = scmutil.match(repo[None], pats, opts)
+    ui.write(('matcher: %r\n' % m))
     items = list(repo[None].walk(m))
     if not items:
         return