Passing keyword only args as positional should fail.

mako/ast.py

@@ -172,6 +172,14 @@ def get_argument_expressions(self, as_call=False):
             else:
                 namedecls.append(name)
 
+        # A bare `*` immediately followed by `**kwargs` is not valid python.
+        # Ie. Using a bare `*` without any named keyword arguments.
+        # A bare `*` and `*args` together is not valid python.
+        # Ie. Using variable positional arguments already means everything
+        # following that argument must be keyword only.
+        if not as_call and kwargnames and not self.varargs:
+            namedecls.append("*")
+
         # Positional arguments
         if self.varargs:
             namedecls.append("*" + argnames.pop(0))

test/test_def.py

@@ -1,6 +1,6 @@
 from mako import lookup
 from mako.template import Template
-from mako.testing.assertions import assert_raises
+from mako.testing.assertions import assert_raises, assert_raises_message
 from mako.testing.assertions import eq_
 from mako.testing.fixtures import TemplateTest
 from mako.testing.helpers import flatten_result
@@ -62,6 +62,23 @@ def test_def_py3k_args(self):
             """look at all these args: one two three four 5 seven""",
         )
 
+    def test_def_py3k_kwonly_as_pos(self):
+        """Test that using position arg for kwonly argument fails."""
+        template = Template(
+            """
+        <%def name="kwonly(one, *, two)">
+            look at all these args: ${one} ${two}"""
+            """
+        </%def>
+
+        ${kwonly('one', 'two')}"""
+        )
+        assert_raises_message(
+            TypeError,
+            "takes 1 positional argument but 2 were given",
+            template.render,
+        )
+
     def test_inter_def(self):
         """test defs calling each other"""
         template = Template(