Allow template to be re-used without persisting assigns

lib/liquid/template.rb

@@ -89,10 +89,11 @@ module Liquid
       when Liquid::Context
         args.shift
       when Hash
-        self.assigns.merge!(args.shift)
-        Context.new(assigns, registers, @rethrow_errors)
+        a = args.shift
+        assigns.each { |k,v| a[k] = v unless a.has_key?(k) }
+        Context.new(a, registers, @rethrow_errors)
       when nil
-        Context.new(assigns, registers, @rethrow_errors)
+        Context.new(assigns.dup, registers, @rethrow_errors)
       else
         raise ArgumentError, "Expect Hash or Liquid::Context as parameter"
       end

test/variable_test.rb

@@ -138,4 +138,23 @@ class VariableResolutionTest < Test::Unit::TestCase
     assert_equal 'worked', template.render
   end
 
+  def test_reuse_parsed_template
+    template = Template.parse(%|{{ greeting }} {{ name }}|)
+    template.assigns['greeting'] = 'Goodbye'
+    assert_equal 'Hello Tobi', template.render('greeting' => 'Hello', 'name' => 'Tobi')
+    assert_equal 'Hello ', template.render('greeting' => 'Hello', 'unknown' => 'Tobi')
+    assert_equal 'Hello Brian', template.render('greeting' => 'Hello', 'name' => 'Brian')
+    assert_equal 'Goodbye Brian', template.render('name' => 'Brian')
+    assert_equal({'greeting'=>'Goodbye'}, template.assigns)
+  end
+
+  def test_assigns_not_polluted_from_template
+    template = Template.parse(%|{{ test }}{% assign test = 'bar' %}{{ test }}|)
+    template.assigns['test'] = 'baz'
+    assert_equal 'bazbar', template.render
+    assert_equal 'bazbar', template.render
+    assert_equal 'foobar', template.render('test' => 'foo')
+    assert_equal 'bazbar', template.render
+  end
+
 end