The if tag now raises Liquid::SyntaxError rather than a generic RuntimeError for syntax problems.

lib/liquid/tags/if.rb

@@ -51,14 +51,14 @@ module Liquid
       else        
         
         expressions = markup.split(/\b(and|or)\b/).reverse
-        raise SyntaxHelp unless expressions.shift =~ Syntax 
+        raise(SyntaxError, SyntaxHelp) unless expressions.shift =~ Syntax 
 
         condition = Condition.new($1, $2, $3)               
         
         while not expressions.empty?
           operator = expressions.shift 
           
-          raise SyntaxHelp unless expressions.shift.to_s =~ Syntax    
+          raise(SyntaxError, SyntaxHelp) unless expressions.shift.to_s =~ Syntax    
           
           new_condition = Condition.new($1, $2, $3)
           new_condition.send(operator.to_sym, condition)     

test/if_else_test.rb

@@ -116,6 +116,10 @@ class IfElseTest < Test::Unit::TestCase
     assert_raise(SyntaxError){ assert_template_result('', '{% if jerry == 1 %}')}
   end
   
+  def test_syntax_error_no_expression
+    assert_raise(SyntaxError) { assert_template_result('', '{% if %}') }
+  end
+  
   def test_if_with_custom_condition
     Condition.operators['contains'] = :[]