--- a/mercurial/templatefilters.py	Sun Mar 18 16:47:44 2018 +0900
+++ b/mercurial/templatefilters.py	Sun Mar 18 16:53:08 2018 +0900
@@ -263,8 +263,7 @@
     elif util.safehasattr(obj, '__iter__'):
         out = [json(i, paranoid) for i in obj]
         return '[' + ', '.join(out) + ']'
-    else:
-        raise TypeError('cannot encode type %s' % obj.__class__.__name__)
+    raise error.ProgrammingError('cannot encode %r' % obj)
 
 @templatefilter('lower', intype=bytes)
 def lower(text):