StrictDefaultUndefined hot fix. See #62.

CHANGES.rst

@@ -1,8 +1,18 @@
 Python Liquid Change Log
 ========================
 
+Version 1.4.1
+-------------
+
+**Hot fix**
+
+- Fixed a bug with the ``StrictDefaultFilter``. It was failing to be strict when
+  accessed by some filter decorators and helpers. Now the ``default`` filter will
+  immediately return its default value if its left value defines a
+  ``force_liquid_default`` property and that property is truthy. See #62.
+
 Version 1.4.0
---------------------------
+-------------
 
 **Features**
 

liquid/__init__.py

@@ -1,7 +1,7 @@
 # flake8: noqa
 # pylint: disable=useless-import-alias,missing-module-docstring
 
-__version__ = "1.4.0"
+__version__ = "1.4.1"
 
 try:
     from markupsafe import escape as escape

liquid/builtin/filters/misc.py

@@ -40,6 +40,12 @@ def size(obj: Any) -> int:
 def default(obj: Any, default_: object = "", *, allow_false: bool = False) -> Any:
     """Return a default value if the input is nil, false, or empty."""
     _obj = obj
+
+    # Return the default value immediately if the object defines a
+    # `force_liquid_default` property.
+    if hasattr(obj, "force_liquid_default") and obj.force_liquid_default:
+        return default_
+
     if hasattr(obj, "__liquid__"):
         _obj = obj.__liquid__()
 

liquid/context.py

@@ -353,12 +353,15 @@ def __reversed__(self) -> Iterable[Any]:
 class StrictDefaultUndefined(StrictUndefined):
     """An undefined that plays nicely with the `default` filter."""
 
+    # Force the `default` filter to return its default value
+    # without inspecting this class type.
+    force_liquid_default = True
+
     # Properties that don't raise an UndefinedError.
     allowed_properties = frozenset(
         [
             "__repr__",
-            "__liquid__",
-            "__class__",
+            "force_liquid_default",
             "name",
             "hint",
             "obj",

tests/test_undefined.py

@@ -238,9 +238,8 @@ def test_debug_undefined_object(self):
     def test_strict_default_undefined(self):
         """Test that we can use an undefined type with the default filter."""
         env = Environment(undefined=StrictDefaultUndefined)
-        undef = DebugUndefined(name="nosuchthing", obj="foo")
         template = env.from_string(r"{{ nosuchthing | default: 'hello' }}")
-        result = template.render(nosuchthing=undef)
+        result = template.render()
         self.assertEqual(result, "hello")
 
         template = env.from_string(r"{{ thing | default: 'hello' }}")
@@ -253,6 +252,23 @@ def test_strict_default_undefined(self):
 
         self.assertEqual(str(raised.exception), "'nosuchthing' is undefined, on line 1")
 
+    def test_filter_strict_default_undefined(self):
+        """Test that the default undefined type raises an exception when used as a
+        filter left value."""
+        env = Environment(undefined=StrictDefaultUndefined)
+        template = env.from_string(r"{{ nosuchthing | floor }}")
+        with self.assertRaises(UndefinedError) as raised:
+            template.render()
+
+        self.assertEqual(str(raised.exception), "'nosuchthing' is undefined, on line 1")
+
+    def test_isinstance_strict_default_filter(self):
+        """Test that the default undefined type raises an exception when accessing
+        __class__."""
+        undef = StrictDefaultUndefined("nosuchthing")
+        with self.assertRaises(UndefinedError):
+            undef.__class__
+
     def test_lax_filter(self):
         """Test that undefined filters can be silently ignored."""
         tests = [