Added Undefined type. Undefined variables get this value if FATAL_UNDEFINED is False

3 files changed, 24 insertions, 6 deletions

diff --git a/scss/expression.py b/scss/expression.py
index 55a1bdd..0b03aa2 100644
--- a/scss/expression.py
+++ b/scss/expression.py
@@ -9,7 +9,7 @@ import six
 
 import scss.config as config
 from scss.cssdefs import COLOR_NAMES, is_builtin_css_function, _expr_glob_re, _interpolate_re, _variable_re
-from scss.types import BooleanValue, ColorValue, ListValue, Null, NumberValue, ParserValue, String
+from scss.types import BooleanValue, ColorValue, ListValue, Null, Undefined, NumberValue, ParserValue, String
 from scss.util import dequote, normalize_var, to_str
 
 ################################################################################
@@ -292,7 +292,8 @@ class CallOp(Expression):
                 u"%s(%s)" % (self.func_name, u", ".join(rendered_args)),
                 quotes=None)
         else:
-            return func(*args, **kwargs)
+            if func is not None and not func.is_null:
+                return func(*args, **kwargs)
 
 class Literal(Expression):
     def __init__(self, value):
@@ -337,8 +338,10 @@ class ArgspecLiteral(Expression):
 def parse_bareword(word):
     if word in COLOR_NAMES:
         return ColorValue.from_name(word)
-    elif word in ('null', 'undefined'):
+    elif word == 'null':
         return Null()
+    elif word == 'undefined':
+        return Undefined()
     elif word == 'true':
         return BooleanValue(True)
     elif word == 'false':
diff --git a/scss/rule.py b/scss/rule.py
index 5b7cbfc..ff445a7 100644
--- a/scss/rule.py
+++ b/scss/rule.py
@@ -2,8 +2,15 @@ from __future__ import absolute_import
 from __future__ import print_function
 
 import six
+import logging
 
 from scss.cssdefs import _has_placeholder_re
+from scss.types import Undefined
+
+log = logging.getLogger(__name__)
+
+
+FATAL_UNDEFINED = False
 
 
 def normalize_var(name):
@@ -29,7 +36,11 @@ class VariableScope(object):
             if key in map:
                 return map[key]
 
-        raise KeyError(key)
+        if FATAL_UNDEFINED:
+            raise KeyError(key)
+
+        log.error("Undefined variable '%s'", key)
+        return Undefined()
 
     def __setitem__(self, key, value):
         for map in self.maps:
diff --git a/scss/types.py b/scss/types.py
index 303e01c..1e314eb 100644
--- a/scss/types.py
+++ b/scss/types.py
@@ -99,7 +99,7 @@ class Null(Value):
         pass
 
     def __str__(self):
-        return 'null'
+        return self.sass_type_name
 
     def __repr__(self):
         return "<%s>" % (type(self).__name__,)
@@ -114,7 +114,11 @@ class Null(Value):
         return isinstance(other, Null)
 
     def render(self, compress=False):
-        return 'null'
+        return self.sass_type_name
+
+
+class Undefined(Null):
+    sass_type_name = u'undefined'
 
 
 class BooleanValue(Value):