Best Practices for Faster PR Reviews


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This post slightly modified from Kubernetes documentation at https://github.com/kubernetes/community/blob/master/contributors/guide/pull-requests.md#best-practices-for-faster-reviews

Best Practices for Faster Reviews

You’ve just had a brilliant idea on how to make a project better. Let’s call that idea Feature-X. Feature-X is not even that complicated. You have a pretty good idea of how to implement it. You jump in and implement it, fixing a bunch of stuff along the way. You send your pull request - this is awesome! And it sits. And sits. A week goes by and nobody reviews it. Finally, someone offers a few comments, which you fix up and wait for more review. And you wait. Another week or two go by. This is horrible.

Let’s talk about best practices so your pull request gets reviewed quickly.

1. Is the feature wanted?

Are you sure Feature-X is something the project team wants or will accept? Is it implemented to fit with other changes in flight? Are you willing to bet a few days or weeks of work on it?

It’s better to get confirmation beforehand. Check the Github issue queue and/or ask!

Even for small changes, it is often a good idea to gather feedback on an issue you filed, or even simply ask in the appropriate Team43 Slack channel or right here to invite discussion and feedback from code owners.

2. Smaller Is Better: Small Commits, Small Pull Requests

Small commits and small pull requests get reviewed faster and are more likely to be correct than big ones.

Attention is a scarce resource. If your pull request takes 60 minutes to review, the reviewer’s eye for detail is not as keen in the last 30 minutes as it was in the first. It might not get reviewed at all if it requires a large continuous block of time from the reviewer.

Breaking up commits

Break up your pull request into multiple commits, at logical break points.

Making a series of discrete commits is a powerful way to express the evolution of an idea or the
different ideas that make up a single feature. Strive to group logically distinct ideas into separate commits.

For example, if you found that Feature-X needed some prefactoring to fit in, make a commit that JUST does that prefactoring. Then make a new commit for Feature-X.

Strike a balance with the number of commits. A pull request with 25 commits is still very cumbersome to review, so use
judgment.

Breaking up Pull Requests

Or, going back to our prefactoring example, you could also fork a new branch, do the prefactoring there and send a pull request for that. If you can extract whole ideas from your pull request and send those as pull requests of their own, you can avoid the painful problem of continually rebasing.

Some of our projects have a fast-moving codebase - lock in your changes ASAP with your small pull request, and make merges be someone else’s problem.

Multiple small pull requests are often better than multiple commits. Don’t worry about flooding us with pull requests. We’d rather have 100 small, obvious pull requests than 10 unreviewable monoliths.

We want every pull request to be useful on its own, so use your best judgment on what should be a pull request vs. a commit.

As a rule of thumb, if your pull request is directly related to Feature-X and nothing else, it should probably be part of the Feature-X pull request. If you can explain why you are doing seemingly no-op work (“it makes the Feature-X change easier, I promise”) we’ll probably be OK with it. If you can imagine someone finding value independently of Feature-X, try it as a pull request. (Do not link pull requests by # in a commit description, because GitHub creates lots of spam. Instead, reference other pull requests via the pull request your commit is in.)

3. Open a Different pull request for Fixes and Generic Features

Put changes that are unrelated to your feature into a different pull request.

Often, as you are implementing Feature-X, you will find bad comments, poorly named functions, bad structure, weak type-safety, etc.

You absolutely should fix those things (or at least file issues, please) - but not in the same pull request as your feature. Otherwise, your diff will have way too many changes, and your reviewer won’t see the forest for the trees.

Look for opportunities to pull out generic features.

For example, if you find yourself touching a lot of modules, think about the dependencies you are introducing between packages. Can some of what you’re doing be made more generic and moved up and out of the Feature-X package? Do you need to use a function or type from an otherwise unrelated package? If so, promote! We have places for hosting more generic code.

Likewise, if Feature-X is similar in form to Feature-W which was checked in last month, and you’re duplicating some tricky stuff from Feature-W, consider prefactoring the core logic out and using it in both Feature-W and
Feature-X. (Do that in its own commit or pull request, please.)

4. Comments Matter

In your code, if someone might not understand why you did something (or you won’t remember why later), comment it. Many code-review comments are about this exact issue.

If you think there’s something pretty obvious that we could follow up on, add a TODO.

5. Test

Nothing is more frustrating than starting a review, only to find that the tests are inadequate or absent. Very few pull requests can touch code and NOT touch tests.

If you don’t know how to test Feature-X, please ask! We’ll be happy to help you design things for easy testing or to suggest appropriate test cases.

6. Squashing and Commit Titles

Your reviewer has finally sent you feedback on Feature-X.

Make the fixups, and don’t squash yet. Put them in a new commit, and re-push. That way your reviewer can look at the new commit on its own, which is much faster than starting over.

We might still ask you to clean up your commits at the very end for the sake of a more readable history, but don’t do this until asked: typically at the point where the pull request would otherwise be tagged LGTM.

Each commit should have a good title line (<70 characters) and include an additional description paragraph describing in more detail the change intended.

General squashing guidelines:

  • Sausage => squash

Do squash when there are several commits to fix bugs in the original commit(s), address reviewer feedback, etc. Really we only want to see the end state and commit message for the whole pull request.

  • Layers => don’t squash

Don’t squash when there are independent changes layered to achieve a single goal. For instance, writing a code munger could be one commit, applying it could be another, and adding a precommit check could be a third. One could argue they should be separate pull requests, but there’s really no way to test/review the munger without seeing it applied, and there needs to be a precommit check to ensure the munged output doesn’t immediately get out of date.

A commit, as much as possible, should be a single logical change.

7. KISS, YAGNI, MVP, etc.

Sometimes we need to remind each other of core tenets of software design - Keep It Simple, You Aren’t Gonna Need It, Minimum Viable Product, and so on. Adding a feature “because we might need it later” is antithetical to software that ships. Add the things you need NOW and (ideally) leave room for things you might need later - but don’t implement them now.

8. It’s OK to Push Back

Sometimes reviewers make mistakes. It’s OK to push back on changes your reviewer requested. If you have a good reason for doing something a certain way, you are absolutely allowed to debate the merits of a requested change. Both the reviewer and reviewee should strive to discuss these issues in a polite and respectful manner.

You might be overruled, but you might also prevail. We’re pretty reasonable people. Mostly.

Another phenomenon of open-source projects (where anyone can comment on any issue) is the dog-pile - your pull request gets so many comments from so many people it becomes hard to follow. In this situation, you can ask the primary reviewer (assignee) whether they want you to fork a new pull request to clear out all the comments. You don’t HAVE to fix every issue raised by every person who feels like commenting, but you should answer reasonable comments with an explanation.

9. Common Sense and Courtesy

No document can take the place of common sense and good taste. Use your best judgment, while you put
a bit of thought into how your work can be made easier to review. If you do these things your pull requests will get merged with less friction.