diff -r e28dedf4ff43 -r 8251c4c4abdc mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Sat Dec 16 12:34:40 2017 -0500
+++ b/mercurial/debugcommands.py	Mon Nov 27 18:48:36 2017 -0500
@@ -1173,6 +1173,11 @@
              fm.formatlist([e.name() for e in wirecompengines
                             if e.wireprotosupport()],
                            name='compengine', fmt='%s', sep=', '))
+    re2 = 'missing'
+    if util._re2:
+        re2 = 'available'
+    fm.plain(_('checking "re2" regexp engine (%s)\n') % re2)
+    fm.data(re2=bool(util._re2))
 
     # templates
     p = templater.templatepaths()