Document / test quirk that kw only args can be passed positionally

Rather than making a backwards incompatible change, document the
quirk and add a test for it.

Fixes: #405
Closes: #406
Pull-request: #406
Pull-request-sha: 0ad95a2

Change-Id: Id66fb5b59c18e60e35479ad553deb7a314ccfaa5

Author: ianjosephwilson

doc/build/defs.rst

@@ -73,6 +73,10 @@ value). This is in contrast to using context-level variables,
 which evaluate to ``UNDEFINED`` if you reference a name that
 does not exist.
 
+Note there is a quirk that results in a bare ``*`` being silently removed from
+a function definition.  The function then incorrectly
+allows keyword only arguments to be used as positional arguments.
+
 Calling Defs from Other Files
 -----------------------------
 

test/test_def.py

@@ -62,6 +62,25 @@ def test_def_py3k_args(self):
             """look at all these args: one two three four 5 seven""",
         )
 
+    def test_def_py3k_args_quirk(self):
+        """Document quirk where bare * is silently removed which incorrectly
+        allows for kwonly args to be passed as positional.
+
+        See issue #405 for more information."""
+        template = Template(
+            """
+        <%def name="kwonly(a, *, b)">
+            hello kwonly: ${a} ${b} """
+            """
+        </%def>
+
+        ${kwonly('1', '2')}"""
+        )
+        eq_(
+            template.render().strip(),
+            """hello kwonly: 1 2""",
+        )
+
     def test_inter_def(self):
         """test defs calling each other"""
         template = Template(