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Run Rails with custom patches
2012-10-04 04:47

I often see comments like this in the Rails bugtracker. Generally, someone is running an older version of Rails, and some bug they face has been fixed on edge. But they may be running a version that's too old to recieve fixes, or need a fix that has yet to be included in an actual release. What to do?

Luckily, Bundler exists. It makes it super easy to run your own Rails. Check it out:

Step 1: Fork you!

Go to GitHub, hit up rails/rails, and click that fork button. My own personal fork of Rails is here, for example, so in the rest of these examples, I'll be using my own username. If you're me, you can use it too, but seriously, stop being me. If you're not me, substitute your own username.

Step 2: apply patch

Let's get our copy going locally:

$ git clone git@github.com:steveklabnik/rails.git
$ cd rails

We'll apply the patch from the example comment above. In this case, the person wants to have this patch work on Rails 3.1.

You have two options here: Rails keeps a branch open for every minor version, and also tags every release. You can pick between the stable branch and a particular release. The stable branch should work just fine, but maybe you're on a specific Rails release for a reason. For example, the latest version of Rails 3.1 is 3.1.8, but this person says they're on 3.1.1. If they use the 3-1-stable branch, they'll also get all the changes from 3.1.1-3.1.8, as well as unreleased changes that may exist on that branch. That's possibly too much for you, so we'll just work off of 3.1.1. This is probably a bad idea, since 3.1.6 included several security fixes, but you're an adult, do dumb things if you want to.

$ git checkout v3.1.1

You'll see a big message about a detached HEAD. Don't worry about it.

If you want the stable branch for extra fixes,

$ git checkout 3-1-stable

Now, it's a good idea to make our own branches, so that we don't get confused with upstream. So let's make a new branch:

$ git checkout -b my_patched_rails

Awesome. Now, we can grab the commit we wanted. We can do this with cherry-pick:

$ git cherry-pick 8fc8763fde2cc685ed63fcf640cfae556252809b

I found this SHA1 by checking out this page, which is linked at the top of the pull request.

If there are multiple commits you need, you can do one of two things: either cherry-pick the merge commit, in which case you'll probably need to pass the -m1 option, or simply cherry-pick them all in order.

You may get conflicts. Yay backporting! If git whines at you, do what you normally do. Resolve the merge, then git commit.

Finally, push it back up to your GitHub:

$ git push origin my_patched_rails

Congrats! You've got your own custom Rails. Now it's time to use it.

Step 3: update Gemfile

Go to your Rails app, and edit this line in your Gemfile:

gem 'rails', "3.1.1"

change it to this:

gem 'rails', :git => "https://github.com/steveklabnik/rails", :branch => "my_patched_rails"

It's that easy! Now bundle:

$ bundle update

You should see it mention something about checking out a certain copy of Rails.

Step 4: Profit!

That's it! Congrats, you're using Rails with your patch.

But I'm on 2.3, I'm not running Bundler!

Do this.