[New Feature] Add forloop inside render tag when using for syntax (#1191)

* Add forloop to render for syntax

* Remove forloop guard

lib/liquid/tags/render.rb

@@ -43,19 +43,26 @@ module Liquid
 
       context_variable_name = @alias_name || template_name.split('/').last
 
-      render_partial_func = ->(var) {
+      render_partial_func = ->(var, forloop) {
         inner_context = context.new_isolated_subcontext
         inner_context.template_name = template_name
         inner_context.partial = true
+        inner_context['forloop'] = forloop if forloop
         @attributes.each do |key, value|
           inner_context[key] = context.evaluate(value)
         end
         inner_context[context_variable_name] = var unless var.nil?
         partial.render_to_output_buffer(inner_context, output)
+        forloop&.send(:increment!)
       }
 
       variable = @variable_name_expr ? context.evaluate(@variable_name_expr) : nil
-      variable.is_a?(Array) ? variable.each(&render_partial_func) : render_partial_func.call(variable)
+      if variable.is_a?(Array)
+        forloop = Liquid::ForloopDrop.new(template_name, variable.count, nil)
+        variable.each { |var| render_partial_func.call(var, forloop) }
+      else
+        render_partial_func.call(variable, nil)
+      end
 
       output
     end

test/integration/tags/render_tag_test.rb

@@ -205,4 +205,13 @@ class RenderTagTest < Minitest::Test
     assert_template_result("Product: Draft 151cm Product: Element 155cm ",
                            "{% render 'product' for products %}", "products" => [{ 'title' => 'Draft 151cm' }, { 'title' => 'Element 155cm' }])
   end
+
+  def test_render_tag_forloop
+    Liquid::Template.file_system = StubFileSystem.new(
+      'product' => "Product: {{ product.title }} {% if forloop.first %}first{% endif %} {% if forloop.last %}last{% endif %} index:{{ forloop.index }} ",
+    )
+
+    assert_template_result("Product: Draft 151cm first  index:1 Product: Element 155cm  last index:2 ",
+                           "{% render 'product' for products %}", "products" => [{ 'title' => 'Draft 151cm' }, { 'title' => 'Element 155cm' }])
+  end
 end