Fixing MozReview's sore spots

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MozReview was intentionally released early, with a fairly minimal feature set, and some ugly things bolted onto a packaged code-review tool. The code-review process at Mozilla hasn’t changed much since the project began—Splinter, a slightly fancier UI than dealing with raw diffs, notwithstanding. We knew this would be a controversial subject, with a variety of (invariably strong) opinions. But we also knew that we couldn’t make meaningful progress on a number of long-desired features, like autolanding commits and automatic code analysis, without moving to a modern repository-based review system. We also knew that, with the incredible popularity of GitHub, many developers expect a workflow that involves them pushing up commits for review in a rich web UI, not exporting discrete patches and looking at almost raw diffs.

Rather than spending a couple years off in isolation developing a polished system that might not hit our goals of both appealing to future Mozillians and increasing productivity overall, we released a very early product—the basic set of features required by a push-based, repository-centric code-review system. Ironically, perhaps, this has decreased the productivity of some people, since the new system is somewhat raw and most definitely a big change from the old. It’s our sincere belief that the pain currently experienced by some people, while definitely regrettable and in some cases unexpected, will be balanced, in the long run, by the opportunities to regularly correct our course and reach the goal of a world-class code review-and-submission system that much faster.

And so, as expected, we’ve received quite a bit of feedback. I’ve been noticing a pattern, which is great, because it gives us insight into classes of problems and needs. I’ve identified four categories, which interestingly correspond to levels of usage, from basic to advanced.

Understanding MozReview’s (and Review Board’s) models

Some users find MozReview very opaque. They aren’t sure what many of the buttons and widgets do, and, in general, are confused by the interface. This caught us a little off-guard but, in retrospect, is understandable. Review Board is a big change from Splinter and much more complex. I believe one of the sources of most confusion is the overall review model, with its various states, views, entry points, and exit points. Splinter has the concept of a review in progress, but it is a lot simpler.

We also had to add the concept of a series of related commits to Review Board, which on its own has essentially a patch-based model, similar to Splinter’s, that’s too limited to build on. The relationship between a parent review request and the individual “child” commits is the source of a lot of bewilderment.

Improving the overall user experience of performing a review is a top priority for the next quarter. I’ll explore the combination of the complexity of Review Board and the commit-series model we added in a follow-up post.

Inconveniences and lack of clarity around some features

For users who are generally satisfied by MozReview, at least, enough to use it without getting too frustrated, there are a number of paper cuts and limitations that can be worked around but generate some annoyance. This is an area we knew we were going to have to improve. We don’t yet have parity with Splinter/Bugzilla attachments, e.g. reviewers can’t delegate review requests, nor can they mark specific files as reviewed. There are other areas that we can go beyond Bugzilla, such as being able to land parts of a commit series (this is technically possible in Bugzilla by having separate patches, but it’s difficult to track). And there are specific things that Review Board has that aren’t as useful for us as they could be, like the dashboard.

This will also be a big part of the work in the next quarter (at least).

Inability to use MozReview at all due to technological limitations

The single biggest item here is lack of support for git, particularly a git interface for hg repos like mozilla-central. There are many people interested in using MozReview, but their work flows are based around git using git-cinnabar. gps and kanru did some initial work around this in bug 1153053; fleshing this out into a proper solution isn’t a small task, but it seems clear that we’ll have to finish it regardless before too long, if we want MozReview to be the central code-review tool at Mozilla. We’re still trying to decide how this fits into the above priorities; more users is good, but making existing users happier is as well.

Big-ticket items

As mentioned at the beginning of this post, the main reason we’re building a new review tool is to make it repository-centric, that is, based around commits, not isolated patches. This makes a lot of long-desired tools and features much more feasible, including autoland, automatic static analysis, commit rewriting to automatically include metadata like reviewers, and a bunch of other things.

This has been a big focus for the last few months. We’ve had autoland-to-try for a little while now, and autoland-to-inbound is nearly complete. We have a generic library for static analysis with which we’ll be able to build various review bots. And, of course, the one big feature we started with, the ability push commits to MozReview instead of exporting standalone patches, which by itself is both more convenient and preserves more information.

After autoland-to-inbound we’ll be putting aside other big features for a little while to concentrate on general user experience so that people enjoy using MozReview, but rest assured we’ll be back here to build more powerful workflows for everyone.

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