# Contributing to Protocol Buffers

We welcome some types of contributions to protocol buffers. This doc describes the
process to contribute patches to protobuf and the general guidelines we
expect contributors to follow.

## What We Accept

* Bug fixes with unit tests demonstrating the problem are very welcome.
  We also appreciate bug reports, even when they don't come with a patch.
  Bug fixes without tests are usually not accepted.
* New APIs and features with adequate test coverage and documentation
  may be accepted if they do not compromise backwards 
  compatibility. However there's a fairly high bar of usefulness a new public
  method must clear before it will be accepted. Features that are fine in 
  isolation are often rejected because they don't have enough impact to justify the 
  conceptual burden and ongoing maintenance cost. It's best to file an issue 
  and get agreement from maintainers on the value of a new feature before
  working on a PR.
* Performance optimizations may be accepted if they have convincing benchmarks that demonstrate 
  an improvement and they do not significantly increase complexity.  
* Changes to existing APIs are almost never accepted. Stability and
  backwards compatibility are paramount. In the unlikely event a breaking change 
  is required, it must usually be implemented in google3 first. 
* Changes to the wire and text formats are never accepted. Any breaking change
  to these formats would have to be implemented as a completely new format.
  We cannot begin generating protos that cannot be parsed by existing code.

## Before You Start

We accept patches in the form of github pull requests. If you are new to
github, please read [How to create github pull requests](https://help.github.com/articles/about-pull-requests/)
first.

### Contributor License Agreements

Contributions to this project must be accompanied by a Contributor License
Agreement. You (or your employer) retain the copyright to your contribution,
this simply gives us permission to use and redistribute your contributions
as part of the project.

* If you are an individual writing original source code and you're sure you
  own the intellectual property, then you'll need to sign an [individual CLA](https://cla.developers.google.com/about/google-individual?csw=1).
* If you work for a company that wants to allow you to contribute your work,
  then you'll need to sign a [corporate CLA](https://cla.developers.google.com/about/google-corporate?csw=1).

### Coding Style

This project follows [Google’s Coding Style Guides](https://github.com/google/styleguide).
Before sending out your pull request, please familiarize yourself with the
corresponding style guides and make sure the proposed code change is style
conforming.

## Contributing Process

Most pull requests should go to the master branch and the change will be
included in the next major/minor version release (e.g., 3.6.0 release). If you
need to include a bug fix in a patch release (e.g., 3.5.2), make sure it’s
already merged to master, and then create a pull request cherry-picking the
commits from master branch to the release branch (e.g., branch 3.5.x).

For each pull request, a protobuf team member will be assigned to review the
pull request. For minor cleanups, the pull request may be merged right away
after an initial review. For larger changes, you will likely receive multiple
rounds of comments and it may take some time to complete. We will try to keep
our response time within 7-days but if you don’t get any response in a few
days, feel free to comment on the threads to get our attention. We also expect
you to respond to our comments within a reasonable amount of time. If we don’t
hear from you for 2 weeks or longer, we may close the pull request. You can
still send the pull request again once you have time to work on it.

Once a pull request is merged, we will take care of the rest and get it into
the final release.

## Pull Request Guidelines

* If you are a Googler, it is preferable to first create an internal CL and
  have it reviewed and submitted. The code propagation process will deliver the
  change to GitHub.
* Create small PRs that are narrowly focused on addressing a single concern.
  We often receive PRs that are trying to fix several things at a time, but if
  only one fix is considered acceptable, nothing gets merged and both author's
  & reviewer's time is wasted. Create more PRs to address different concerns and
  everyone will be happy.
* For speculative changes, consider opening an issue and discussing it first.
  If you are suggesting a behavioral or API change, make sure you get explicit
  support from a protobuf team member before sending us the pull request.
* Provide a good PR description as a record of what change is being made and
  why it was made. Link to a GitHub issue if it exists.
* Don't fix code style and formatting unless you are already changing that
  line to address an issue. PRs with irrelevant changes won't be merged. If
  you do want to fix formatting or style, do that in a separate PR.
* Unless your PR is trivial, you should expect there will be reviewer comments
  that you'll need to address before merging. We expect you to be reasonably
  responsive to those comments, otherwise the PR will be closed after 2-3 weeks
  of inactivity.
* Maintain clean commit history and use meaningful commit messages. PRs with
  messy commit history are difficult to review and won't be merged. Use rebase
  -i upstream/master to curate your commit history and/or to bring in latest
  changes from master (but avoid rebasing in the middle of a code review).
* Keep your PR up to date with upstream/master (if there are merge conflicts,
  we can't really merge your change).
* All tests need to be passing before your change can be merged. We recommend
  you run tests locally before creating your PR to catch breakages early on.
  Ultimately, the green signal will be provided by our testing infrastructure.
  The reviewer will help you if there are test failures that seem not related
  to the change you are making.

## Reviewer Guidelines

* Make sure that all tests are passing before approval.
* Apply the "release notes: yes" label if the pull request's description should
  be included in the next release (e.g., any new feature / bug fix).
  Apply the "release notes: no" label if the pull request's description should
  not be included in the next release (e.g., refactoring changes that does not
  change behavior, integration from Google internal, updating tests, etc.).
* Apply the appropriate language label (e.g., C++, Java, Python, etc.) to the
  pull request. This will make it easier to identify which languages the pull
  request affects, allowing us to better identify appropriate reviewer, create
  a better release note, and make it easier to identify issues in the future.
