Contributing to the Feed

Contributor License Agreement

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. Head over to to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you‘ve already submitted one (even if it was for a different project), you probably don’t need to do it again.

Patch Acceptance Process

  1. Prepare a git commit that implements the feature. Don't forget to add tests.

  2. Ensure you've signed a Contributor License Agreement.

  3. Create a new code review on Gerrit.

    1. Have an automatically generated “Change Id” line in your commit message. If you haven't used Gerrit before, it will print a bash command to create the git hook and then you will need to run git commit --amend to add the line.

      See the Gerrit documentation for more information about uploading changes.

  4. Wait for Feed team member to assign you a reviewer.

  5. Complete a code review. Amend your existing commit and re-push to make changes to your patch.

  6. An engineer at Google applies the patch to our internal version control system. The patch is exported as a Git commit, at which point the Gerrit code review is closed.

Coding Standards


All pull requests must follow the Google Java style guide.

Build Targets

Use java_library when possible, and android_library when the sources depend on an android_library or Android code.

Library Size

A key feature of this library is its low impact on method count and dex size. In order to maintain this key feature of the library, we have developed a set of best practices. While maintaining a low impact is important, these best practices balance the need of low impact with the necessity of code health.

  1. Avoid enums. Use @IntDef and @StringDef instead.

  2. Limit the use of Protobufs. Protobufs add a lot of methods compared to a simple POJO. In some cases Protobufs are necessary or appropriate, such as when serialization is required and the protobuf message evolves. If using Protobufs, follow these guidelines:

    1. Avoid using has() if possible.
    2. Only use builders when necessary. In some cases you may only need to read from a proto. In these cases, builders can be avoided.
    3. Limit the use of enums. These produce a lot of methods.
  3. Trust Proguard to optimize certain things:

    1. Proguard will eliminate synthetic accessors, so don't artificially increase visibility of variables when used in lambdas or anonymous classes. If your IDE warns you about these, you can turn the warning off.
    2. Proguard will inline simple getters, so don't sacrifice encapsulation by exposing fields directly.
    3. Proguard will inline small helper methods, especially if they don‘t have dependencies on the class instance (i.e. they’re static). Prefer many small methods to few large methods.
  4. For internal code (I.e. not exposed to hosts), don't declare an interface if there is only one concrete implementation.

Compiling and Testing

Feed libraries use Bazel in order to build. Bazel must first be setup to build Android apps. See here for instructions on how to setup Bazel for Android.

After setting up Bazel the following command will build all Feed libraries: bazel build src/main/... The following can then be used to run all Feed library tests: bazel test src/test/...