Debugging exceptions Rails 5 jbuilder views

There comes a time where regardless of your unit testing you have errors in production. But, alas, the exception isn't in your controller itself but the view!

There has been a quick and dirty way of getting the full stack trace in console for a while but it fails to hit the mark in Rails 4 and Rails 5.

Below is the full copy/paste snippet that will let you try and render a view in console. Very helpful with JSON APIs that use jbuilder that can have complex logic and multiple partial inheritance. Any error or exception will generate a full stack trace for you to debug with.

def rendered_view(view_path, variables = {})  
  view = ActionView::Base.new(Rails.configuration.paths['app/views'], variables)
  view.extend ApplicationHelper
  view.class_eval do
    include Rails.application.routes.url_helpers
    include ApplicationHelper
    def protect_against_forgery?
      false
    end
  end
  view.render(file: view_path)
end  

Example

Given a view like below

# views/api/users/show.json.jbuilder
json.foo  foo  
json.user @user.id  

Use the helper method you'd use in production console like so to get the exception stack trace:

rendered_view('api/users/show', { 'user' => User.find(123), 'foo' => 'bar' })  
# => ActionView::Template::Error: some exception you're debugging for
#        from ...
#        from ...
#        ...

Or once you've resolved the error:

# => "{\"foo\":\"bar\":,\"user\":123}"

Happy hunting!

This posts's header is by Matthew Potter. Used under CC BY 2.0 license.