Committer Guide

This guide is for committers and covers Beam’s guidelines for reviewing and merging code.

Pull request review objectives

The review process aims for:

Granularity of changes:

Always get to LGTM (“Looks good to me!”)

After a pull request goes through rounds of reviews and revisions, it will become ready for merge. A reviewer signals their approval either by GitHub “approval” or by a comment such as “Looks good to me!” (LGTM).

Once a pull request is approved, any committer can merge it.

Exceptions to this rule are rare and made on a case-by-case basis. A committer may use their discretion for situations such as build breaks. In this case, you should still seek a review on the pull request! A common acronym you may see is “TBR” – “to be reviewed”.

Always go through a pull request, even if you won’t wait for the code review. Committers should never commit anything without going through a pull request, even when it is an urgent fix or rollback due to build breakage. Skipping pull request bypasses test coverage and could potentially cause the build to fail, or fail to fix breakage. In addition, pull requests ensure that changes are communicated properly and potential flaws or improvements can be spotted, even after the merge happens.

Contributor License Agreement

If you are merging a larger contribution, please make sure that the contributor has an ICLA on file with the Apache Secretary. You can view the list of committers here, as well as ICLA-signers who aren’t yet committers.

For smaller contributions, however, this is not required. In this case, we rely on clause five of the Apache License, Version 2.0, describing licensing of intentionally submitted contributions.

Tests

Before merging, please make sure that Jenkins tests pass, as visible in the GitHub pull request. Do not merge the pull request if there are test failures.

If the pull request contains changes that call for extra test coverage, you can ask Jenkins to run an extended test suite. For example, if the pull request modifies a runner, you can run the full ValidatesRunner suite with a comment such as “Run Spark ValidatesRunner”. You can run the examples and some IO integration tests with “Run Java PostCommit”.

Finishing touches

At some point in the review process, the change to the codebase will be complete. However, the pull request may have a collection of review-related commits that are not meaningful to preserve in the history. The reviewer should give the LGTM and then request that the author of the pull request rebase, squash, split, etc, the commits, so that the history is most useful:

Merging it!

While it is preferred that authors squash commits after review is complete, there may be situations where it is more practical for the committer to handle this (such as when the action to be taken is obvious or the author isn’t available). The committer may use the “Squash and merge” option in Github (or modify the PR commits in other ways). The committer is ultimately responsible and we “trust the committer’s judgment”!

After all the tests pass, there should be a green merge button at the bottom of the pull request. There are multiple choices. Unless you want to squash commits as part of the merge (see above) you should choose “Merge pull request” and ensure “Create a merge commit” is selected from the drop down. This preserves the commit history and adds a merge commit, so be sure the commit history has been curated appropriately.

Do not use the default GitHub commit message, which looks like this:

Merge pull request #1234 from some_user/transient_branch_name

[BEAM-7873] Fix the foo bizzle bazzle

Instead, pull it all into the subject line:

Merge pull request #1234: [BEAM-7873] Fix the foo bizzle bazzle

If you have comments to add, put them in the body of the commit message.