--- a/mercurial/templater.py	Wed May 27 13:22:48 2015 -0700
+++ b/mercurial/templater.py	Mon Jun 15 13:31:22 2015 -0500
@@ -266,7 +266,7 @@
 
     def getpatterns(i):
         if i < len(args):
-            s = args[i][1].strip()
+            s = stringify(args[i][0](context, mapping, args[i][1])).strip()
             if s:
                 return [s]
         return []