Adds, by name, a renderer or renderers to the _renderers available to call within controller actions.

It is useful when rendering from an ActionController::Metal controller or otherwise to add an available renderer proc to a specific controller.

Both ActionController::Base and ActionController::API include ActionController::Renderers::All, making all renderers available in the controller. See Renderers::RENDERERS and Renderers.add.

Since ActionController::Metal controllers cannot render, the controller must include AbstractController::Rendering, ActionController::Rendering, and ActionController::Renderers, and have at least one renderer.

Rather than including ActionController::Renderers::All and including all renderers, you may specify which renderers to include by passing the renderer name or names to use_renderers. For example, a controller that includes only the :json renderer (_render_with_renderer_json) might look like:

class MetalRenderingController < ActionController::Metal
  include AbstractController::Rendering
  include ActionController::Rendering
  include ActionController::Renderers

  use_renderers :json

  def show
    render json: record
  end
end

You must specify a use_renderer, else the controller.renderer and controller._renderers will be nil, and the action will fail.