Pull Request Linting as a Service: Lintron is Revelry’s Code Review Robot

I’m here to tell you the story of Lintron, our pull request linting robot. Lintron is a tool that we built to, basically, perform code reviews as a service. It automatically lints all code in all of our pull requests at Revelry. We’ve been using it constantly, and we’ve had amazing results.

Before Lintron

Before Lintron, our code quality standards and style guides lived mostly in our heads. They were interpreted and enforced differently by different code reviewers. Also, reviewers had to comment on each code quality or style issue by hand. This approach made a lot of busy work for reviewers and resulted in code that wasn’t as consistent as we wanted.

It was silly. We had people doing static analysis that could be done by robots.

So I made Lintron.

What is Lintron?

Lintron listens for pull request webhooks. Then, it retrieves the PR and its files from GitHub. It runs each file through one or more linters (determined by file extension) and then uses the GitHub comments API to list any violations immediately next to the corresponding line of code in the diff (see the screenshot at the top of this post). It ignores violations on lines that the PR doesn’t touch.

pull request robot

Lintron, our pull request robot, is a Rails application with no database. PRs are linted immediately, and Lintron retains no local state. I used the GitHub API as the only data store. I wrapped each linter in a common interface (i.e. the adapter pattern) so that the application code stays extremely simple.

Lintron currently has adapters for these linters:

The results have been great

Within weeks of deploying Lintron, our code style had become much more consistent. The robot’s consistent eye has also saved us from many code smells and logic issues that might’ve escaped human reviewers.

When we create a new code standard, we don’t send around a memo. We update Lintron. Within a week, everyone figures out the new rule and writes better code.

The most important result is that reviewers can now focus on providing substantive feedback, rather than spending their time on rote style issues.

As Joel said:

joel on pull request robot

You can use it too!

If you want to try Lintron out, the source is available on Revelry’s GitHub repo.

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