Simplify FilterExpression.args_check

django/template/base.py

@@ -622,34 +622,17 @@ class FilterExpression(object):
 
     def args_check(name, func, provided):
         provided = list(provided)
-        plen = len(provided)
+        # First argument, filter input, is implied.
+        plen = len(provided) + 1
         # Check to see if a decorator is providing the real function.
         func = getattr(func, '_decorated_function', func)
         args, varargs, varkw, defaults = getargspec(func)
-        # First argument is filter input.
-        args.pop(0)
-        if defaults:
-            nondefs = args[:-len(defaults)]
-        else:
-            nondefs = args
-        # Args without defaults must be provided.
-        try:
-            for arg in nondefs:
-                provided.pop(0)
-        except IndexError:
-            # Not enough
+        alen = len(args)
+        dlen = len(defaults or [])
+        # Not enough OR Too many
+        if plen < (alen - dlen) or plen > alen:
             raise TemplateSyntaxError("%s requires %d arguments, %d provided" %
-                                      (name, len(nondefs), plen))
-
-        # Defaults can be overridden.
-        defaults = list(defaults) if defaults else []
-        try:
-            for parg in provided:
-                defaults.pop(0)
-        except IndexError:
-            # Too many.
-            raise TemplateSyntaxError("%s requires %d arguments, %d provided" %
-                                      (name, len(nondefs), plen))
+                                      (name, alen - dlen, plen))
 
         return True
     args_check = staticmethod(args_check)

tests/template_tests/test_parser.py

@@ -6,7 +6,7 @@ from __future__ import unicode_literals
 from unittest import TestCase
 
 from django.template import (TokenParser, FilterExpression, Parser, Variable,
-    Template, TemplateSyntaxError)
+    Template, TemplateSyntaxError, Library)
 from django.test.utils import override_settings
 from django.utils import six
 
@@ -94,3 +94,42 @@ class ParserTests(TestCase):
         with six.assertRaisesRegex(self, TemplateSyntaxError, msg) as cm:
             Template("{% if 1 %}{{ foo@bar }}{% endif %}")
         self.assertEqual(cm.exception.django_template_source[1], (10, 23))
+
+    def test_filter_args_count(self):
+        p = Parser("")
+        l = Library()
+        @l.filter
+        def no_arguments(value):
+            pass
+        @l.filter
+        def one_argument(value, arg):
+            pass
+        @l.filter
+        def one_opt_argument(value, arg=False):
+            pass
+        @l.filter
+        def two_arguments(value, arg, arg2):
+            pass
+        @l.filter
+        def two_one_opt_arg(value, arg, arg2=False):
+            pass
+        p.add_library(l)
+        for expr in (
+                '1|no_arguments:"1"',
+                '1|two_arguments',
+                '1|two_arguments:"1"',
+                '1|two_one_opt_arg',
+            ):
+            with self.assertRaises(TemplateSyntaxError):
+                FilterExpression(expr, p)
+        for expr in (
+                # Correct number of arguments
+                '1|no_arguments',
+                '1|one_argument:"1"',
+                # One optional
+                '1|one_opt_argument',
+                '1|one_opt_argument:"1"',
+                # Not supplying all
+                '1|two_one_opt_arg:"1"',
+            ):
+            FilterExpression(expr, p)