From 47fbff07fa9184dfbedd9ad536fb192378f27c3f Mon Sep 17 00:00:00 2001
From: Chris AtLee <chris.atlee@shopify.com>
Date: Tue, 18 Jan 2022 18:08:43 -0500
Subject: [PATCH] WIP - Support {% render obj %}

---
 lib/liquid.rb                            |  1 +
 lib/liquid/locales/en.yml                |  1 +
 lib/liquid/renderabledrop.rb             |  9 ++++++
 lib/liquid/tags/render.rb                | 37 ++++++++++++++++++++----
 test/integration/tags/render_tag_test.rb |  5 ++--
 5 files changed, 44 insertions(+), 9 deletions(-)
 create mode 100644 lib/liquid/renderabledrop.rb

diff --git a/lib/liquid.rb b/lib/liquid.rb
index 28337943..4849c7c1 100644
--- a/lib/liquid.rb
+++ b/lib/liquid.rb
@@ -64,6 +64,7 @@ require 'liquid/strainer_template'
 require 'liquid/expression'
 require 'liquid/context'
 require 'liquid/parser_switching'
+require 'liquid/renderabledrop'
 require 'liquid/tag'
 require 'liquid/tag/disabler'
 require 'liquid/tag/disableable'
diff --git a/lib/liquid/locales/en.yml b/lib/liquid/locales/en.yml
index eb35d868..33adc9b7 100644
--- a/lib/liquid/locales/en.yml
+++ b/lib/liquid/locales/en.yml
@@ -24,5 +24,6 @@
       render: "Syntax error in tag 'render' - Template name must be a quoted string"
     argument:
       include: "Argument error in tag 'include' - Illegal template name"
+      render: "Argument error in tag 'render' - Illegal template name"
     disabled:
       tag: "usage is not allowed in this context"
diff --git a/lib/liquid/renderabledrop.rb b/lib/liquid/renderabledrop.rb
new file mode 100644
index 00000000..2894ac39
--- /dev/null
+++ b/lib/liquid/renderabledrop.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Liquid
+  class RenderableDrop < Drop
+    def render(_context, _output)
+      raise NotImplementedError, "render must be implemented for #{self.class.name}"
+    end
+  end
+end
diff --git a/lib/liquid/tags/render.rb b/lib/liquid/tags/render.rb
index 6380249c..295fbd6a 100644
--- a/lib/liquid/tags/render.rb
+++ b/lib/liquid/tags/render.rb
@@ -3,7 +3,20 @@
 module Liquid
   class Render < Tag
     FOR = 'for'
-    SYNTAX = /(#{QuotedString}+)(\s+(with|#{FOR})\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
+    SYNTAX = %r{
+      (
+        ## for {% render "snippet" %}
+        #{Liquid::QuotedString}+ |
+        ## for {% render block %}
+        \A#{Liquid::VariableSegment}+
+      )
+      ## for {% render "snippet" with product as p %}
+      ## or  {% render "snippet" for products p %}
+      (\s+(with|#{Liquid::Render::FOR})\s+(#{Liquid::QuotedFragment}+))?
+      (\s+(?:as)\s+(#{Liquid::VariableSegment}+))?
+      ## variables passed into the tag (e.g. {% render "snippet", var1: value1, var2: value2 %}
+      ## are not matched by this regex and are handled by .initialize
+    }xo
 
     disable_tags "include"
 
@@ -14,13 +27,13 @@ module Liquid
 
       raise SyntaxError, options[:locale].t("errors.syntax.render") unless markup =~ SYNTAX
 
-      template_name = Regexp.last_match(1)
+      @template_name = Regexp.last_match(1)
       with_or_for = Regexp.last_match(3)
       variable_name = Regexp.last_match(4)
 
       @alias_name = Regexp.last_match(6)
       @variable_name_expr = variable_name ? parse_expression(variable_name) : nil
-      @template_name_expr = parse_expression(template_name)
+      @template_name_expr = parse_expression(@template_name)
       @for = (with_or_for == FOR)
 
       @attributes = {}
@@ -34,9 +47,21 @@ module Liquid
     end
 
     def render_tag(context, output)
-      # Though we evaluate this here we will only ever parse it as a string literal.
-      template_name = context.evaluate(@template_name_expr)
-      raise ArgumentError, options[:locale].t("errors.argument.include") unless template_name
+      render_target = context.evaluate(@template_name_expr)
+      raise ArgumentError, options[:locale].t("errors.argument.render") unless render_target
+
+      # Check to see if this is a renderable drop
+      if render_target.is_a?(Liquid::RenderableDrop)
+        return render_target.render(context, output)
+      end
+
+      # Otherwise it must be a quoted string
+      unless /#{Liquid::QuotedString}+/.match?(@template_name)
+        output << "<!-- #{options[:locale].t('errors.syntax.render')} -->"
+        return
+      end
+
+      template_name = render_target
 
       partial = PartialCache.load(
         template_name,
diff --git a/test/integration/tags/render_tag_test.rb b/test/integration/tags/render_tag_test.rb
index 1af22b9b..c17de80d 100644
--- a/test/integration/tags/render_tag_test.rb
+++ b/test/integration/tags/render_tag_test.rb
@@ -75,9 +75,8 @@ class RenderTagTest < Minitest::Test
   def test_dynamically_choosen_templates_are_not_allowed
     Liquid::Template.file_system = StubFileSystem.new('snippet' => 'should not be rendered')
 
-    assert_raises(Liquid::SyntaxError) do
-      Liquid::Template.parse("{% assign name = 'snippet' %}{% render name %}")
-    end
+    assert_equal("<!-- Syntax error in tag 'render' - Template name must be a quoted string -->",
+      Liquid::Template.parse("{% assign name = 'snippet' %}{% render name %}").render!)
   end
 
   def test_include_tag_caches_second_read_of_same_partial