rejects variables like a/b in for loops, closes #150

lib/liquid/tags/for.rb

@@ -44,7 +44,7 @@ module Liquid
   # forloop.last:: Returns true if the item is the last item.
   #
   class For < Block
-    Syntax = /(\w+)\s+in\s+(#{QuotedFragment}+)\s*(reversed)?/o
+    Syntax = /\A(\w+)\s+in\s+(#{QuotedFragment}+)\s*(reversed)?/o
 
     def initialize(tag_name, markup, tokens)
       if markup =~ Syntax

test/liquid/tags/for_tag_test.rb

@@ -281,4 +281,10 @@ HERE
   def test_blank_string_not_iterable
     assert_template_result('', "{% for char in characters %}I WILL NOT BE OUTPUT{% endfor %}", 'characters' => '')
   end
+
+  def test_bad_variable_naming_in_for_loop
+    assert_raise(Liquid::SyntaxError) do
+      Liquid::Template.parse('{% for a/b in x %}{% endfor %}')
+    end
+  end
 end