--- a/mercurial/registrar.py	Mon Mar 19 20:39:06 2018 +0900
+++ b/mercurial/registrar.py	Sun Mar 18 15:14:58 2018 +0900
@@ -324,7 +324,7 @@
 
         templatefilter = registrar.templatefilter()
 
-        @templatefilter('myfilter')
+        @templatefilter('myfilter', intype=bytes)
         def myfilterfunc(text):
             '''Explanation of this template filter ....
             '''
@@ -332,6 +332,9 @@
 
     The first string argument is used also in online help.
 
+    Optional argument 'intype' defines the type of the input argument,
+    which should be (bytes, int, or None for any.)
+
     'templatefilter' instance in example above can be used to
     decorate multiple functions.
 
@@ -342,6 +345,9 @@
     Otherwise, explicit 'templatefilters.loadkeyword()' is needed.
     """
 
+    def _extrasetup(self, name, func, intype=None):
+        func._intype = intype
+
 class templatefunc(_templateregistrarbase):
     """Decorator to register template function