Best Way to Debug Third-Party Gems in Ruby

Best way to debug third-party gems in ruby

I would love to know if there's a better way to do this, but how I usually do it is:

1. Add the ruby-debug gem to your Gemfile (or ruby-debug19 if you're on Ruby 1.9.2)
2. Find the Gem by doing bundle show gemname. I'm on a Mac so I usually pipe this to pbcopy so it gets copied to my clipboard. bundle show rails | pbcopy
3. Open the gem directory in your favorite editor. mvim /path/to/gem/directory
4. Navigate to the file and line where you want to put the breakpoint* and insert debugger above the line in question.
5. Reload page, run test, or do whatever you would to get the Gem file to execute
6. When execution stops at debugger, you can inspect variables (p variable_name), and move line by line with the ruby debugger commands.

*Knowing where to put the breakpoint can take some understanding of the code, but you should start in lib/gemname.rb

Process for debugging a third-party gem

Use :path in the project's gemfile.

You are working on gem my_gem and project my_project at the same time. To make this painless use this in the gemfile of your project

# in /path/to/my_project/Gemfile
...

gem 'my_gem', :path => '/path/to/my_gem'

...

And then you can iterate without having to build the gem all time.

There's isn't even a need to rename the gem.

How to debug a plugin / gem? (with useful notes to setup and use ruby-debug gem)

I highly recommend you learn to use ruby-debug. You can install it by doing:

gem install ruby-debug

You can then add a debugger statement to your code either in the plugin code or where your code calls the plugin, step through it, and see what's going wrong.

I also personally use these settings which makes it a bit easier to use - put them in a ~/.rdebugrc file.

set autoeval
set autolist
set autoreload

rails: How to log response & request of 3rd party gem?

As it says in the active_shipping docs:

To log requests and responses, just set the logger on your carrier class to some kind of Logger object:

ActiveShipping::USPS.logger = Logger.new($stdout)

Can I access the source of a ruby block without &block?

So, the real issue here is that I didn't read all the Pry help (specifically rescue-pry) and didn't know about the up command...

Usage: up [OPTIONS]
  Go up to the caller's context. Accepts optional numeric parameter for how many frames to move up.
  Also accepts a string (regex) instead of numeric; for jumping to nearest parent method frame which matches the regex.
  e.g: up      #=> Move up 1 stack frame.
  e.g: up 3    #=> Move up 2 stack frames.
  e.g: up meth #=> Jump to nearest parent stack frame whose method matches /meth/ regex, i.e `my_method`.

    -h, --help      Show this message.

By executing up within a pry session from a raised exception, I was able to get to the block where the exception was raised and inspect the local variables I needed.

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