One Man’s Walk in work

Wouldn’t it be nice if when an error happened in your application, you could not only see the stack trace, but click on a line and jump to the offending code? This is not groundbreaking stuff, I know, I had this like 10 years ago in C++ and later Java fat clients, and I’m sure other languages & IDEs had it too – but somehow in moving to writing web apps in Ruby, I lost it.

I want it back damnit!

Turns out it’s pretty easy to get back (at least it is if you use textmate) – check it out.

Custom Error Page

First, to get a custom error page for your project, add something like this to your application.rb :

def rescue_action_locally(*args)
  render :template  => "application/public_error", :layout => false
end
 
alias rescue_action_in_public render_action_locally

Note, if you’re using exception notifiable, you probably want to change the last line to something like :

alias render_404 rescue_action_locally
alias render_500 rescue_action_locally

We use markaby, so our public_error template looks something like this; it’s probably a good idea to keep this simple and not use a layout, just in case the error came from the layout :

html do
  head do
    title action_name
    stylesheet_link_tag 'error'
  end
  body do
    div.error do
      div.message do
        h1 "Whoops"
 
        p "We detected an error.  Don't worry, though, 
we've been notified and we're on it."
      end
    end
  end
end

Adding a Stack Trace w/ Links to the Error Page

So, it would be helpful to us for our error page to tell us more in our development and staging environments. We do use exception notifiable, so we don’t actually need or want it to say anything else to a real user in production. Adding this to our template, it now looks like this :

html do
  head do
    title action_name
    stylesheet_link_tag 'error'
  end
  body do
    div.error do
      div.message do
        h1 "Whoops"
 
        p "We detected an error.  Don't worry, though, 
we've been notified and we're on it."
      end
 
      if RAILS_ENV != 'production'
        div.stack_trace do
          h2 "Stack Trace"
          div { link_to_code $!.to_s.to_s.gsub("\n", "
") }
          hr
          div { link_to_code $!.backtrace.join("
") }
        end
      end
    end
  end
end

What’s that “link_to_code” method in there?

It’s a method in application_helper that replaces any path with a textmate url to open up that file on your local system and jump to the offending line. Check it out :

def link_to_code(text)
  text.gsub(/([\w\.-]*\/[\w\/\.-]+)\:(\d+)/) do |match|
    file = $1.starts_with?("/") ? $1 : File.join(RAILS_ROOT, $1)
    link_to match, "txmt://open?url=file://#{file}&line=#{$2}"
  end
end

That’s it. Suddenly, stack traces are friendly again!

Tags: rails, ruby, testing

This entry was posted on Wednesday, April 30th, 2008 at 6:29 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.