**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.**

Contributing to Ruby on Rails
=============================

This guide covers ways in which _you_ can become a part of the ongoing development of Ruby on Rails.

After reading this guide, you will know:

* How to use GitHub to report issues.
* How to clone master and run the test suite.
* How to help resolve existing issues.
* How to contribute to the Ruby on Rails documentation.
* How to contribute to the Ruby on Rails code.

Ruby on Rails is not "someone else's framework." Over the years, thousands of people have contributed to Ruby on Rails ranging from a single character to massive architectural changes or significant documentation - all with the goal of making Ruby on Rails better for everyone. Even if you don't feel up to writing code or documentation yet, there are a variety of other ways that you can contribute, from reporting issues to testing patches.

As mentioned in [Rails'
README](https://github.com/rails/rails/blob/master/README.md), everyone interacting in Rails and its sub-projects' codebases, issue trackers, chat rooms, and mailing lists is expected to follow the Rails [code of conduct](http://rubyonrails.org/conduct/).

--------------------------------------------------------------------------------

Reporting an Issue
------------------

Ruby on Rails uses [GitHub Issue Tracking](https://github.com/rails/rails/issues) to track issues (primarily bugs and contributions of new code). If you've found a bug in Ruby on Rails, this is the place to start. You'll need to create a (free) GitHub account in order to submit an issue, to comment on them or to create pull requests.

NOTE: Bugs in the most recent released version of Ruby on Rails are likely to get the most attention. Also, the Rails core team is always interested in feedback from those who can take the time to test _edge Rails_ (the code for the version of Rails that is currently under development). Later in this guide, you'll find out how to get edge Rails for testing.

### Creating a Bug Report

If you've found a problem in Ruby on Rails which is not a security risk, do a search on GitHub under [Issues](https://github.com/rails/rails/issues) in case it has already been reported. If you are unable to find any open GitHub issues addressing the problem you found, your next step will be to [open a new one](https://github.com/rails/rails/issues/new). (See the next section for reporting security issues.)

Your issue report should contain a title and a clear description of the issue at the bare minimum. You should include as much relevant information as possible and should at least post a code sample that demonstrates the issue. It would be even better if you could include a unit test that shows how the expected behavior is not occurring. Your goal should be to make it easy for yourself - and others - to reproduce the bug and figure out a fix.

Then, don't get your hopes up! Unless you have a "Code Red, Mission Critical, the World is Coming to an End" kind of bug, you're creating this issue report in the hope that others with the same problem will be able to collaborate with you on solving it. Do not expect that the issue report will automatically see any activity or that others will jump to fix it. Creating an issue like this is mostly to help yourself start on the path of fixing the problem and for others to confirm it with an "I'm having this problem too" comment.

### Create an Executable Test Case

Having a way to reproduce your issue will be very helpful for others to help confirm, investigate and ultimately fix your issue. You can do this by providing an executable test case. To make this process easier, we have prepared several bug report templates for you to use as a starting point:

* Template for Active Record (models, database) issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_master.rb)
* Template for testing Active Record (migration) issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_migrations_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_migrations_master.rb)
* Template for Action Pack (controllers, routing) issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/action_controller_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/action_controller_master.rb)
* Template for Active Job issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_job_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_job_master.rb)
* Generic template for other issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/generic_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/generic_master.rb)

These templates include the boilerplate code to set up a test case against either a released version of Rails (`*_gem.rb`) or edge Rails (`*_master.rb`).

Simply copy the content of the appropriate template into a `.rb` file and make the necessary changes to demonstrate the issue. You can execute it by running `ruby the_file.rb` in your terminal. If all goes well, you should see your test case failing.

You can then share your executable test case as a [gist](https://gist.github.com), or simply paste the content into the issue description.

### Special Treatment for Security Issues

WARNING: Please do not report security vulnerabilities with public GitHub issue reports. The [Rails security policy page](http://rubyonrails.org/security) details the procedure to follow for security issues.

### What about Feature Requests?

Please don't put "feature request" items into GitHub Issues. If there's a new
feature that you want to see added to Ruby on Rails, you'll need to write the
code yourself - or convince someone else to partner with you to write the code.
Later in this guide, you'll find detailed instructions for proposing a patch to
Ruby on Rails. If you enter a wish list item in GitHub Issues with no code, you
can expect it to be marked "invalid" as soon as it's reviewed.

Sometimes, the line between 'bug' and 'feature' is a hard one to draw.
Generally, a feature is anything that adds new behavior, while a bug is
anything that causes incorrect behavior. Sometimes,
the core team will have to make a judgment call. That said, the distinction
generally just affects which release your patch will get in to; we love feature
submissions! They just won't get backported to maintenance branches.

If you'd like feedback on an idea for a feature before doing the work to make
a patch, please send an email to the [rails-core mailing
list](https://groups.google.com/forum/?fromgroups#!forum/rubyonrails-core). You
might get no response, which means that everyone is indifferent. You might find
someone who's also interested in building that feature. You might get a "This
won't be accepted." But it's the proper place to discuss new ideas. GitHub
Issues are not a particularly good venue for the sometimes long and involved
discussions new features require.


Helping to Resolve Existing Issues
----------------------------------

As a next step beyond reporting issues, you can help the core team resolve existing issues. If you check the [issues list](https://github.com/rails/rails/issues) in GitHub Issues, you'll find lots of issues already requiring attention. What can you do for these? Quite a bit, actually:

### Verifying Bug Reports

For starters, it helps just to verify bug reports. Can you reproduce the reported issue on your own computer? If so, you can add a comment to the issue saying that you're seeing the same thing.

If an issue is very vague, can you help narrow it down to something more specific? Maybe you can provide additional information to help reproduce a bug, or help by eliminating needless steps that aren't required to demonstrate the problem.

If you find a bug report without a test, it's very useful to contribute a failing test. This is also a great way to get started exploring the source code: looking at the existing test files will teach you how to write more tests. New tests are best contributed in the form of a patch, as explained later on in the "[Contributing to the Rails Code](#contributing-to-the-rails-code)" section.

Anything you can do to make bug reports more succinct or easier to reproduce helps folks trying to write code to fix those bugs - whether you end up writing the code yourself or not.

### Testing Patches

You can also help out by examining pull requests that have been submitted to Ruby on Rails via GitHub. In order to apply someone's changes, you need to first create a dedicated branch:

```bash
$ git checkout -b testing_branch
```

Then, you can use their remote branch to update your codebase. For example, let's say the GitHub user JohnSmith has forked and pushed to a topic branch "orange" located at https://github.com/JohnSmith/rails.

```bash
$ git remote add JohnSmith https://github.com/JohnSmith/rails.git
$ git pull JohnSmith orange
```

After applying their branch, test it out! Here are some things to think about:

* Does the change actually work?
* Are you happy with the tests? Can you follow what they're testing? Are there any tests missing?
* Does it have the proper documentation coverage? Should documentation elsewhere be updated?
* Do you like the implementation? Can you think of a nicer or faster way to implement a part of their change?

Once you're happy that the pull request contains a good change, comment on the GitHub issue indicating your approval. Your comment should indicate that you like the change and what you like about it. Something like:

>I like the way you've restructured that code in generate_finder_sql - much nicer. The tests look good too.

If your comment simply reads "+1", then odds are that other reviewers aren't going to take it too seriously. Show that you took the time to review the pull request.

Contributing to the Rails Documentation
---------------------------------------

Ruby on Rails has two main sets of documentation: the guides, which help you
learn about Ruby on Rails, and the API, which serves as a reference.

You can help improve the Rails guides by making them more coherent, consistent or readable, adding missing information, correcting factual errors, fixing typos, or bringing them up to date with the latest edge Rails.

To do so, open a pull request to [Rails](https://github.com/rails/rails) on GitHub.

When working with documentation, please take into account the [API Documentation Guidelines](api_documentation_guidelines.html) and the [Ruby on Rails Guides Guidelines](ruby_on_rails_guides_guidelines.html).

NOTE: To help our CI servers you should add [ci skip] to your documentation commit message to skip build on that commit. Please remember to use it for commits containing only documentation changes.

Translating Rails Guides
------------------------

We are happy to have people volunteer to translate the Rails guides. Just follow these steps:

* Fork https://github.com/rails/rails.
* Add a source folder for your own language, for example: *guides/source/it-IT* for Italian.
* Copy the contents of *guides/source* into your own language directory and translate them.
* Do NOT translate the HTML files, as they are automatically generated.

Note that translations are not submitted to the Rails repository. As detailed above, your work happens in a fork. This is so because in practice documentation maintenance via patches is only sustainable in English.

To generate the guides in HTML format cd into the *guides* directory then run (eg. for it-IT):

```bash
$ bundle install
$ bundle exec rake guides:generate:html GUIDES_LANGUAGE=it-IT
```

This will generate the guides in an *output* directory.

NOTE: The instructions are for Rails > 4. The Redcarpet Gem doesn't work with JRuby.

Translation efforts we know about (various versions):

* **Italian**: [https://github.com/rixlabs/docrails](https://github.com/rixlabs/docrails)
* **Spanish**: [https://github.com/gramos/docrails/wiki](https://github.com/gramos/docrails/wiki)
* **Polish**: [https://github.com/apohllo/docrails](https://github.com/apohllo/docrails)
* **French** : [https://github.com/railsfrance/docrails](https://github.com/railsfrance/docrails)
* **Czech** : [https://github.com/rubyonrails-cz/docrails/tree/czech](https://github.com/rubyonrails-cz/docrails/tree/czech)
* **Turkish** : [https://github.com/ujk/docrails](https://github.com/ujk/docrails)
* **Korean** : [https://github.com/rorlakr/rails-guides](https://github.com/rorlakr/rails-guides)
* **Simplified Chinese** : [https://github.com/ruby-china/guides](https://github.com/ruby-china/guides)
* **Traditional Chinese** : [https://github.com/docrails-tw/guides](https://github.com/docrails-tw/guides)
* **Russian** : [https://github.com/morsbox/rusrails](https://github.com/morsbox/rusrails)
* **Japanese** : [https://github.com/yasslab/railsguides.jp](https://github.com/yasslab/railsguides.jp)

Contributing to the Rails Code
------------------------------

### Setting Up a Development Environment

To move on from submitting bugs to helping resolve existing issues or contributing your own code to Ruby on Rails, you _must_ be able to run its test suite. In this section of the guide, you'll learn how to setup the tests on your own computer.

#### The Easy Way

The easiest and recommended way to get a development environment ready to hack is to use the [rails-dev-box](https://github.com/rails/rails-dev-box).

#### The Hard Way

In case you can't use the Rails development box, see [this other guide](development_dependencies_install.html).

### Clone the Rails Repository

To be able to contribute code, you need to clone the Rails repository:

```bash
$ git clone https://github.com/rails/rails.git
```

and create a dedicated branch:

```bash
$ cd rails
$ git checkout -b my_new_branch
```

It doesn't matter much what name you use, because this branch will only exist on your local computer and your personal repository on GitHub. It won't be part of the Rails Git repository.

### Bundle install

Install the required gems.

```bash
$ bundle install
```

### Running an Application Against Your Local Branch

In case you need a dummy Rails app to test changes, the `--dev` flag of `rails new` generates an application that uses your local branch:

```bash
$ cd rails
$ bundle exec rails new ~/my-test-app --dev
```

The application generated in `~/my-test-app` runs against your local branch
and in particular sees any modifications upon server reboot.

### Write Your Code

Now get busy and add/edit code. You're on your branch now, so you can write whatever you want (make sure you're on the right branch with `git branch -a`). But if you're planning to submit your change back for inclusion in Rails, keep a few things in mind:

* Get the code right.
* Use Rails idioms and helpers.
* Include tests that fail without your code, and pass with it.
* Update the (surrounding) documentation, examples elsewhere, and the guides: whatever is affected by your contribution.


TIP: Changes that are cosmetic in nature and do not add anything substantial to the stability, functionality, or testability of Rails will generally not be accepted (read more about [our rationales behind this decision](https://github.com/rails/rails/pull/13771#issuecomment-32746700)).

#### Follow the Coding Conventions

Rails follows a simple set of coding style conventions:

* Two spaces, no tabs (for indentation).
* No trailing whitespace. Blank lines should not have any spaces.
* Indent after private/protected.
* Use Ruby >= 1.9 syntax for hashes. Prefer `{ a: :b }` over `{ :a => :b }`.
* Prefer `&&`/`||` over `and`/`or`.
* Prefer class << self over self.method for class methods.
* Use `my_method(my_arg)` not `my_method( my_arg )` or `my_method my_arg`.
* Use `a = b` and not `a=b`.
* Use assert_not methods instead of refute.
* Prefer `method { do_stuff }` instead of `method{do_stuff}` for single-line blocks.
* Follow the conventions in the source you see used already.

The above are guidelines - please use your best judgment in using them.

### Benchmark Your Code

For changes that might have an impact on performance, please benchmark your
code and measure the impact. Please share the benchmark script you used as well
as the results. You should consider including this information in your commit
message, which allows future contributors to easily verify your findings and
determine if they are still relevant. (For example, future optimizations in the
Ruby VM might render certain optimizations unnecessary.)

It is very easy to make an optimization that improves performance for a
specific scenario you care about but regresses on other common cases.
Therefore, you should test your change against a list of representative
scenarios. Ideally, they should be based on real-world scenarios extracted
from production applications.

You can use the [benchmark template](https://github.com/rails/rails/blob/master/guides/bug_report_templates/benchmark.rb)
as a starting point. It includes the boilerplate code to setup a benchmark
using the [benchmark-ips](https://github.com/evanphx/benchmark-ips) gem. The
template is designed for testing relatively self-contained changes that can be
inlined into the script.

### Running Tests

It is not customary in Rails to run the full test suite before pushing
changes. The railties test suite in particular takes a long time, and takes an
especially long time if the source code is mounted in `/vagrant` as happens in
the recommended workflow with the [rails-dev-box](https://github.com/rails/rails-dev-box).

As a compromise, test what your code obviously affects, and if the change is
not in railties, run the whole test suite of the affected component. If all
tests are passing, that's enough to propose your contribution. We have
[Travis CI](https://travis-ci.org/rails/rails) as a safety net for catching
unexpected breakages elsewhere.

#### Entire Rails:

To run all the tests, do:

```bash
$ cd rails
$ bundle exec rake test
```

#### For a Particular Component

You can run tests only for a particular component (e.g. Action Pack). For example,
to run Action Mailer tests:

```bash
$ cd actionmailer
$ bundle exec rake test
```

#### Running a Single Test

You can run a single test through ruby. For instance:

```bash
$ cd actionmailer
$ bundle exec ruby -w -Itest test/mail_layout_test.rb -n test_explicit_class_layout
```

The `-n` option allows you to run a single method instead of the whole
file.

#### Testing Active Record

First, create the databases you'll need. You can find a list of the required
table names, usernames, and passwords in `activerecord/test/config.example.yml`.

For MySQL and PostgreSQL, running the SQL statements `create database
activerecord_unittest` and `create database activerecord_unittest2` is
sufficient. This is not necessary for SQLite3.

This is how you run the Active Record test suite only for SQLite3:

```bash
$ cd activerecord
$ bundle exec rake test:sqlite3
```

You can now run the tests as you did for `sqlite3`. The tasks are respectively:

```bash
test:mysql2
test:postgresql
```

Finally,

```bash
$ bundle exec rake test
```

will now run the three of them in turn.

You can also run any single test separately:

```bash
$ ARCONN=sqlite3 bundle exec ruby -Itest test/cases/associations/has_many_associations_test.rb
```

To run a single test against all adapters, use:

```bash
$ bundle exec rake TEST=test/cases/associations/has_many_associations_test.rb
```

You can invoke `test_jdbcmysql`, `test_jdbcsqlite3` or `test_jdbcpostgresql` also. See the file `activerecord/RUNNING_UNIT_TESTS.rdoc` for information on running more targeted database tests, or the file `ci/travis.rb` for the test suite run by the continuous integration server.

### Warnings

The test suite runs with warnings enabled. Ideally, Ruby on Rails should issue no warnings, but there may be a few, as well as some from third-party libraries. Please ignore (or fix!) them, if any, and submit patches that do not issue new warnings.

If you are sure about what you are doing and would like to have a more clear output, there's a way to override the flag:

```bash
$ RUBYOPT=-W0 bundle exec rake test
```

### Updating the CHANGELOG

The CHANGELOG is an important part of every release. It keeps the list of changes for every Rails version.

You should add an entry **to the top** of the CHANGELOG of the framework that you modified if you're adding or removing a feature, committing a bug fix or adding deprecation notices. Refactorings and documentation changes generally should not go to the CHANGELOG.

A CHANGELOG entry should summarize what was changed and should end with the author's name. You can use multiple lines if you need more space and you can attach code examples indented with 4 spaces. If a change is related to a specific issue, you should attach the issue's number. Here is an example CHANGELOG entry:

```
*   Summary of a change that briefly describes what was changed. You can use multiple
    lines and wrap them at around 80 characters. Code examples are ok, too, if needed:

        class Foo
          def bar
            puts 'baz'
          end
        end

    You can continue after the code example and you can attach issue number. GH#1234

    *Your Name*
```

Your name can be added directly after the last word if there are no code
examples or multiple paragraphs. Otherwise, it's best to make a new paragraph.

### Updating the Gemfile.lock

Some changes require the dependencies to be upgraded. In these cases make sure you run `bundle update` to get the right version of the dependency and commit the `Gemfile.lock` file within your changes.

### Commit Your Changes

When you're happy with the code on your computer, you need to commit the changes to Git:

```bash
$ git commit -a
```

This should fire up your editor to write a commit message. When you have
finished, save and close to continue.

A well-formatted and descriptive commit message is very helpful to others for
understanding why the change was made, so please take the time to write it.

A good commit message looks like this:

```
Short summary (ideally 50 characters or less)

More detailed description, if necessary. It should be wrapped to
72 characters. Try to be as descriptive as you can. Even if you
think that the commit content is obvious, it may not be obvious
to others. Add any description that is already present in the
relevant issues; it should not be necessary to visit a webpage
to check the history.

The description section can have multiple paragraphs.

Code examples can be embedded by indenting them with 4 spaces:

    class ArticlesController
      def index
        render json: Article.limit(10)
      end
    end

You can also add bullet points:

- make a bullet point by starting a line with either a dash (-)
  or an asterisk (*)

- wrap lines at 72 characters, and indent any additional lines
  with 2 spaces for readability
```

TIP. Please squash your commits into a single commit when appropriate. This
simplifies future cherry picks and keeps the git log clean.

### Update Your Branch

It's pretty likely that other changes to master have happened while you were working. Go get them:

```bash
$ git checkout master
$ git pull --rebase
```

Now reapply your patch on top of the latest changes:

```bash
$ git checkout my_new_branch
$ git rebase master
```

No conflicts? Tests still pass? Change still seems reasonable to you? Then move on.

### Fork

Navigate to the Rails [GitHub repository](https://github.com/rails/rails) and press "Fork" in the upper right hand corner.

Add the new remote to your local repository on your local machine:

```bash
$ git remote add mine https://github.com/<your user name>/rails.git
```

Push to your remote:

```bash
$ git push mine my_new_branch
```

You might have cloned your forked repository into your machine and might want to add the original Rails repository as a remote instead, if that's the case here's what you have to do.

In the directory you cloned your fork:

```bash
$ git remote add rails https://github.com/rails/rails.git
```

Download new commits and branches from the official repository:

```bash
$ git fetch rails
```

Merge the new content:

```bash
$ git checkout master
$ git rebase rails/master
```

Update your fork:

```bash
$ git push origin master
```

If you want to update another branch:

```bash
$ git checkout branch_name
$ git rebase rails/branch_name
$ git push origin branch_name
```


### Issue a Pull Request

Navigate to the Rails repository you just pushed to (e.g.
https://github.com/your-user-name/rails) and click on "Pull Requests" seen in
the right panel. On the next page, press "New pull request" in the upper right
hand corner.

Click on "Edit", if you need to change the branches being compared (it compares
"master" by default) and press "Click to create a pull request for this
comparison".

Ensure the changesets you introduced are included. Fill in some details about
your potential patch including a meaningful title. When finished, press "Send
pull request". The Rails core team will be notified about your submission.

### Get some Feedback

Most pull requests will go through a few iterations before they get merged.
Different contributors will sometimes have different opinions, and often
patches will need to be revised before they can get merged.

Some contributors to Rails have email notifications from GitHub turned on, but
others do not. Furthermore, (almost) everyone who works on Rails is a
volunteer, and so it may take a few days for you to get your first feedback on
a pull request. Don't despair! Sometimes it's quick, sometimes it's slow. Such
is the open source life.

If it's been over a week, and you haven't heard anything, you might want to try
and nudge things along. You can use the [rubyonrails-core mailing
list](https://groups.google.com/forum/#!forum/rubyonrails-core) for this. You can also
leave another comment on the pull request.

While you're waiting for feedback on your pull request, open up a few other
pull requests and give someone else some! I'm sure they'll appreciate it in
the same way that you appreciate feedback on your patches.

### Iterate as Necessary

It's entirely possible that the feedback you get will suggest changes. Don't get discouraged: the whole point of contributing to an active open source project is to tap into the knowledge of the community. If people are encouraging you to tweak your code, then it's worth making the tweaks and resubmitting. If the feedback is that your code doesn't belong in the core, you might still think about releasing it as a gem.

#### Squashing commits

One of the things that we may ask you to do is to "squash your commits", which
will combine all of your commits into a single commit. We prefer pull requests
that are a single commit. This makes it easier to backport changes to stable
branches, squashing makes it easier to revert bad commits, and the git history
can be a bit easier to follow. Rails is a large project, and a bunch of
extraneous commits can add a lot of noise.

In order to do this, you'll need to have a git remote that points at the main
Rails repository. This is useful anyway, but just in case you don't have it set
up, make sure that you do this first:

```bash
$ git remote add upstream https://github.com/rails/rails.git
```

You can call this remote whatever you'd like, but if you don't use `upstream`,
then change the name to your own in the instructions below.

Given that your remote branch is called `my_pull_request`, then you can do the
following:

```bash
$ git fetch upstream
$ git checkout my_pull_request
$ git rebase -i upstream/master

< Choose 'squash' for all of your commits except the first one. >
< Edit the commit message to make sense, and describe all your changes. >

$ git push origin my_pull_request -f
```

You should be able to refresh the pull request on GitHub and see that it has
been updated.

#### Updating pull request

Sometimes you will be asked to make some changes to the code you have
already committed. This can include amending existing commits. In this
case Git will not allow you to push the changes as the pushed branch
and local branch do not match. Instead of opening a new pull request,
you can force push to your branch on GitHub as described earlier in
squashing commits section:

```bash
$ git push origin my_pull_request -f
```

This will update the branch and pull request on GitHub with your new code. Do
note that using force push may result in commits being lost on the remote branch; use it with care.


### Older Versions of Ruby on Rails

If you want to add a fix to older versions of Ruby on Rails, you'll need to set up and switch to your own local tracking branch. Here is an example to switch to the 4-0-stable branch:

```bash
$ git branch --track 4-0-stable origin/4-0-stable
$ git checkout 4-0-stable
```

TIP: You may want to [put your Git branch name in your shell prompt](http://qugstart.com/blog/git-and-svn/add-colored-git-branch-name-to-your-shell-prompt/) to make it easier to remember which version of the code you're working with.

#### Backporting

Changes that are merged into master are intended for the next major release of Rails. Sometimes, it might be beneficial for your changes to propagate back to the maintenance releases for older stable branches. Generally, security fixes and bug fixes are good candidates for a backport, while new features and patches that introduce a change in behavior will not be accepted. When in doubt, it is best to consult a Rails team member before backporting your changes to avoid wasted effort.

For simple fixes, the easiest way to backport your changes is to [extract a diff from your changes in master and apply them to the target branch](http://ariejan.net/2009/10/26/how-to-create-and-apply-a-patch-with-git).

First, make sure your changes are the only difference between your current branch and master:

```bash
$ git log master..HEAD
```

Then extract the diff:

```bash
$ git format-patch master --stdout > ~/my_changes.patch
```

Switch over to the target branch and apply your changes:

```bash
$ git checkout -b my_backport_branch 4-2-stable
$ git apply ~/my_changes.patch
```

This works well for simple changes. However, if your changes are complicated or if the code in master has deviated significantly from your target branch, it might require more work on your part. The difficulty of a backport varies greatly from case to case, and sometimes it is simply not worth the effort.

Once you have resolved all conflicts and made sure all the tests are passing, push your changes and open a separate pull request for your backport. It is also worth noting that older branches might have a different set of build targets than master. When possible, it is best to first test your backport locally against the Ruby versions listed in `.travis.yml` before submitting your pull request.

And then... think about your next contribution!

Rails Contributors
------------------

All contributions get credit in [Rails Contributors](http://contributors.rubyonrails.org).
