Use Pry in gems without modifying the Gemfile or using `require`

Question

I am trying to debug a gem that\'s used by a Rails app.

I cloned the Gem locally to go prying around (and also allows me to do nice things such as git bisect

Answer 1

Jon from the past! As you know, I have the answers to (almost) all your problems.

In this case, you're actually describing two problems: (a) you can't require 'pry' when Pry is not in the Gemfile, (b) you can't use Pry if you don't require it.

What Bundler does, as Conrad Irwin writes:

Bundler is an awesome gem that gives you a good degree of confidence that "if it works in development, it works in production". It can do this by being vicious about gem dependencies: if it's not in the Gemfile, it's not getting required. It also ensures that everyone's development environment is identical, no more does "it works on my machine" cut it as an excuse.

There are circumstances when this dogmatic dedication to duty can get in the way. In particular all good developers have set up their development environment very personally. Obviously, it's not important that my local tools work in production, and it's positively bad for productivity if everyone is forced to have an identicial development setup.

So in doing all the good things Bundler does for us Ruby developers, it comes by design with a caveat: "what's outside the bundle/Gemfile (eg system gems) doesn't exist anymore." How it does that is by redefining the require process and changes your PATH so that it only sees what's in the bundle.

That means you can't use Pry at all without polluting the Gemfile, you say, right? Not so fast. Conrad Irwin being the smart little cookie that he is, came up with a solution and made Pry Debundle, a gem that temporarily reverses the patches Bundler made to our require.

So all you have to do is just require 'pry-debundle' then, right? Oh... wait. Yep, Debundle is probably not in the Gemfile.

The monkey fix is to hard copy the source of pry-debundle.rb to ~/debundle.rb, and then load that. (For now, you'll need Pry loaded to run that source file, but you can run only the debundle! method to get there, require Pry, and go prying around. A little monkeypatching is needed, but I'm working on a PR.)