Debugging Ruby and Rails on Pry

Railscasts has a very good screencast regarding http://railscasts.com/episodes/280-pry-with-rails. The Pry screencast from Joshua Cheek is also very useful as an introduction to Pry, going inside a class, inspecting it, showing instance variables, etc.

In your Gemfile, you can add the pry gems in the development group

group :development, :test do
  . . .
  gem 'better_errors'
  gem 'binding_of_caller'
  gem 'meta_request'
 
  # Pry gems related to debugging. Move this outside the development group
  # in case production debugging is necessary. Note, pry-debugger works
  # in production and conflicts locally with RubyMine, use pry-nav + ~/.pryrc instead.
  # Unfortunately pry-nav does not work in production, so you are left with
  # pry-debugger.
  #
  # Locally where RubyMine exists:
  # group :development, :test do
  #   gem 'pry'
  #   gem 'pry-remote'
  #   gem 'pry-nav'
  # end
  #
  # Production Debugging: See config/environments/production.rb
  # gem 'pry'
  # gem 'pry-remote'
  # gem 'pry-debugger'
 
  gem 'pry'
  gem 'pry-remote'
  gem 'pry-nav'
end

Create a ~/.pryrc

Pry.config.correct_indent = false
Pry.config.auto_indent = false
Pry.commands.alias_command 'c', 'continue'
Pry.commands.alias_command 's', 'step'
Pry.commands.alias_command 'n', 'next'
Pry.commands.alias_command 'f', 'finish' # Only works in pry-debugger gem

To debug, add binding.pry. Execution will stop where you specify binding.pry

     5: def index
     6:   poller
     7:   binding.pry
     8: 
     9:   if current_user.admin?
    10:     @notices = Notice.updated_descending
    11:   else
    12:     @notices = current_user.client.notices.approved.updated_descending
    13:   end
    14: 
    15: end

To navigate, you can use the navigation aliases on step 2
To use pry instead of the rails console

pry -r ./config/environment

To remotely debug a rails application you can use pry-remote. Instead of using binding.pry we use binding.remote_pry. From there, you can use pry normally and navigate using our navigation aliases (step 2). See also http://blog.bignerdranch.com/1629-debugging-remote-processes-with-pry-remote/

On the server:

     5: def index
     6:   poller
     7:   binding.remote_pry
     8: 
     9:   if current_user.admin?
    10:     @notices = Notice.updated_descending
    11:   else
    12:     @notices = current_user.client.notices.approved.updated_descending
    13:   end
    14: 
    15: end

On the client:

# pry-remote -h 127.0.0.1 -p 9876
     5: def index
     6:   poller
   =>7:   binding.remote_pry
     8: 
     9:   if current_user.admin?
    10:     @notices = Notice.updated_descending
    11:   else
    12:     @notices = current_user.client.notices.approved.updated_descending
    13:   end
    14: 
    15: end

Note: If you experience issues with pry unable to exit or continue. You might need to specify the proper Pry.config settings. Since, we have a rails app + apache passenger and having .pryrc doesn’t seem to work, I specified the Pry.config settings in my config/environments/production.rb and moved the gems out of development (irk!). From there, it works as expected.

MyApp::Application.configure do
   . . .
 
   # Settings for PRY debugging in production. Yes, it is enabled, use with caution
   # as you really need to know what you are doing. If you are uncommenting the lines below
   # then you should have a very good reason why. If you are doing this in production too often,
   # then you are not writing more tests! When you are finished debugging, please
   # do comment the lines below.
   Pry.config.correct_indent = false
   Pry.config.auto_indent = false
   Pry.config.history.file = "#{Rails.root}/log/pry_history.log"
   Pry.commands.alias_command 'c', 'continue'
   Pry.commands.alias_command 's', 'step'
   Pry.commands.alias_command 'n', 'next'
   Pry.commands.alias_command 'f', 'finish'
 
end

~~One thing that broke is debugging with RubyMine after I used pry. I’ll take a stab on this another day.~~

RuntimeError - Debugger.start is not called yet.:
  debugger (1.6.1) lib/ruby-debug/processor.rb:144:in `at_breakpoint'
  (eval):5:in `block in at_breakpoint'
  <internal:prelude>:10:in `synchronize'
  (eval):3:in `at_breakpoint'
  debugger (1.6.1) lib/ruby-debug-base.rb:41:in `at_breakpoint'

Update 1: pry-debugger has a gem dependency with debugger which conflicts with RubyMine’s debugging gems. See step 1 which now has updated gems. To uninstall pry-debugger and debugger, simply do:

# gem uninstall pry-debugger
# gem uninstall debugger

References:

http://railscasts.com/episodes/280-pry-with-rails
Pry screencast from Joshua Cheek
https://github.com/pry/pry/wiki/Remote-sessions
https://github.com/pry/pry/wiki