`RenderingHelper` supports rendering objects that `respond_to?` `:render_in`

Co-authored-by: Natasha Umer <natashau@github.com>
Co-authored-by: Aaron Patterson <tenderlove@github.com>
Co-authored-by: Shawn Allen <shawnbot@github.com>
Co-authored-by: Emily Plummer <emplums@github.com>
Co-authored-by: Diana Mounter <broccolini@github.com>
Co-authored-by: John Hawthorn <jhawthorn@github.com>
Co-authored-by: Nathan Herald <myobie@github.com>
Co-authored-by: Zaid Zawaideh <zawaideh@github.com>
Co-authored-by: Zach Ahn <engineering@zachahn.com>

2 files changed, 63 insertions, 0 deletions

diff --git a/actionview/test/lib/test_component.rb b/actionview/test/lib/test_component.rb
new file mode 100644
index 0000000000..493b9487b1
--- /dev/null
+++ b/actionview/test/lib/test_component.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+class TestComponent < ActionView::Base
+  include ActiveModel::Validations
+
+  validates :content, :title, presence: true
+  delegate :render, to: :view_context
+
+  def initialize(title:)
+    @title = title
+  end
+
+  # Entrypoint for rendering. Called by ActionView::RenderingHelper#render.
+  #
+  # Returns ActionView::OutputBuffer.
+  def render_in(view_context, &block)
+    self.class.compile
+    @view_context = view_context
+    @content = view_context.capture(&block) if block_given?
+    validate!
+    rendered_template
+  end
+
+  def self.template
+    <<~'erb'
+    <span title="<%= title %>"><%= content %> (<%= render(plain: "Inline render") %>)</span>
+    erb
+  end
+
+  def self.compile
+    @compiled ||= nil
+    return if @compiled
+
+    class_eval(
+      "def rendered_template; @output_buffer = ActionView::OutputBuffer.new; " +
+      ActionView::Template::Handlers::ERB.erb_implementation.new(template, trim: true).src +
+      "; end"
+    )
+
+    @compiled = true
+  end
+
+private
+
+  attr_reader :content, :title, :view_context
+end
diff --git a/actionview/test/template/render_test.rb b/actionview/test/template/render_test.rb
index 2235a7816f..c82264a170 100644
--- a/actionview/test/template/render_test.rb
+++ b/actionview/test/template/render_test.rb
@@ -2,6 +2,8 @@
 
 require "abstract_unit"
 require "controller/fake_models"
+require "test_component"
+require "active_model/validations"
 
 class TestController < ActionController::Base
 end
@@ -670,6 +672,21 @@ module RenderTestCases
   def test_render_throws_exception_when_no_extensions_passed_to_register_template_handler_function_call
     assert_raises(ArgumentError) { ActionView::Template.register_template_handler CustomHandler }
   end
+
+  def test_render_component
+    assert_equal(
+      %(<span title="my title">Hello, World! (Inline render)</span>),
+      @view.render(TestComponent.new(title: "my title")) { "Hello, World!" }.strip
+    )
+  end
+
+  def test_render_component_with_validation_error
+    error = assert_raises(ActiveModel::ValidationError) do
+      @view.render(TestComponent.new(title: "my title")).strip
+    end
+
+    assert_match "Content can't be blank", error.message
+  end
 end
 
 class CachedViewRenderTest < ActiveSupport::TestCase