I spend a lot of my time on pull requests. I have a few thoughts about what works and what doesn't in the pull request process.
Be a good requester
TLDR: Make it easy for reviewers.
As the person creating a pull request, you're going to be asking reviewers for some of their time and attention; both are finite, so do what you can to make it easy for them. It'll help you get this change in faster and, if you keep it up, might earn you a reputation in your company as someone who does good work and is thoughtful.
Keep it small (if you can)
Small, focused pull requests from short-lived feature branches have the easiest time getting merged. They are:
- Quicker and more digestible (and reviewers are less likely to bail)
- Less likely to need lengthy rework if you've taken a wrong turn
- Less likely to get conflicted with the main branch and need manual resolution
In reality you'll sometimes need to do a large change that takes several days or even weeks to finish, but that doesn't mean you should sit on one branch for that time and raise a "big bang" pull request at the end. Instead, find ways to split it up into smaller changes that can be done incrementally without breaking anything.
For example, you might be doing some preparatory refactoring to lay the groundwork for your new functionality, or bolstering test coverage of existing behaviour to give you the confidence to start making changes. Both are good candidates for a pull request in their own right.
Once you get into actually adding your new functionality, keep to this mantra of small and incremental changes. Try working from the outside in --- starting with the UI or the API entry point, stubbing the next layer in as you go, and using feature flags to keep it hidden until it's ready. As well as preventing you from drifting off the mainline and/or doing too-big pull requests, this approach gives you a chance to tag expert reviewers when working in their area, without dragging in too many people at a time.
Away from the actual code, there are a few things you can do to make sure your pull request is approachable.
Don't leave the description blank. Use it to clearly outline:
- The reason for the changes
- What they consist of at a high level
- What behaviour they produce
This should give reviewers some good context for what they're about to see, and save them having to go off and read issue descriptions or acceptance criteria. If the changes have a non-trivial UI impact, think about adding a couple of screenshots.
If you can predict any queries that reviewers might have, try to address them pre-emptively by adding comments yourself, inline with the code. You can call out mitigating factors and/or other approaches that were considered and discarded.
Finally, spend five minutes looking over the pull request yourself before you add any reviewers; you'll be amazed how often you find typos, commented-out code you forgot to delete, defunct tests etc. This will save your reviewers time and might save you some embarassment.
Choice of reviewers
Pull requests are a really good opportunity for people to learn, so it's a bit of a waste if just one person is tagged for review (especially if it's always the same person). On the flipside, having the whole team tagged on every pull request can become a source of distraction, and makes it more likely that no one will review as each person expects that someone else will get to it. So figure out what works for your team here on the balance of throughput and knowledge sharing.
Also, think about people outside the immediate team: is there someone who has worked in this area a lot and could give some valuable feedback, or someone who's expressed an interest in a tool or technique you've used and might like to see what you've done?
If there's one person whose approval you really want before you're happy to merge, make sure you tell them, so they can avoid being an unwitting blocker.
Be a good reviewer
TLDR: Be nice.
There will be times when you aren't going to review a pull request you've been tagged on. It might be that you're too busy to give it the proper attention in a timely manner, or that you don't feel you're best-placed to give a meaningful review, given your skills/knowledge etc. Either way, say so.
Critique with care
Coming into a code review, resist the urge to go straight in and start commenting on stuff that jumps out at you. Instead, do a quick pass over the whole pull request --- the answers to your questions might be in there, if you take a minute to look.
When you do come to leave some critical feedback, think carefully about what to say and how. As with most communication that isn't face-to-face, it's easy to come across like a jerk even if you don't mean to, so it's worth going out of your way to be cordial and constructive. When you've spotted a problem, consider putting to the requester as a question, like "Not sure, but this looks to me like it will break if the second argument is null, could you add a test to check?", or "This might read better using a stream, what do you think?".
Many comments or suggestions you add will be subjective to some degree, so it's good to provide information that supports your point of view. For example, if you're pointing out that some internal standard or convention is being broken, link to where the standards are documented, and to a conforming example elsewhere in the codebase. If you are suggesting a different tool or technique for something, link to an article that explains it.
Also, don't forget about positive feedback. As much as anything else, a review is a chance for you to call out any good stuff you see. The odd "This is a nice pattern, would like to see more of it" won't do any harm, and might provide a bit of balance if you have left some more critical feedback elsewhere.
If you find yourself leaving comments on pull requests about code style (indents, spacing, etc), something is wrong. Tools like ESLint and Prettier were built to do exactly this sort of thing, so get going with one now if you haven't already. Being told your code doesn't look right hurts your feelings; better that it comes from a robot than a person.
Aside from stylistic stuff, if you find yourself repeatedly picking up on the same pitfall or anti-pattern in code reviews, look into whether you can automate that too; many lint tools provide a way to write custom rules.
Should you even do pull requests though?
I think the article cited there is a very fair critique of the way that pull requests often work in practise. Long-lived branches and big pull requests sitting around for days aren't good on any level - but it doesn't have to be that way. There are some great approaches outlined in the article that you can use with pull requests to avoid them becoming a bottleneck, like pairing as you go.