Hunting the Shmoo

One of the pleasures of working at Mozilla, has been learning and using the Mercurial version control system. Over the past decade, I’ve spent countless hours tinkering my worfklow to be just so. Reading docs and articles, meticulously tweaking settings and even writing an extension.

I used to be very passionate about Mercurial. But as time went on, the culture at Mozilla started changing. More and more repos were created in Github, and more and more developers started using git-cinnabar to work on mozilla-central. Then my role changed and I found that 90% of my work was happening outside of mozilla-central and the Mercurial garden I had created for myself.

So it was with a sense of resigned inevitability that I took the news that Mozilla would be migrating mozilla-central to Git. The fire in me was all but extinguished, I was resigned to my fate. And what’s more, I had to agree. The time had come for Mozilla to officially make the switch.

Glandium wrote an excellent post outlining some of the history of the decisions made around version control, putting them into the context of the time. In that post, he offers some compelling wisdom to Mercurial holdouts like myself:

I’ll swim against the current here, and say this: the earlier you can switch to git, the earlier you’ll find out what works and what doesn’t work for you, whether you already know Git or not.

When I read that, I had to agree. But, I just couldn’t bring myself to do it. No, if I was going to have to give up my revsets and changeset obsolesence and my carefully curated workflows, then so be it. But damnit! I was going to continue using them for as long as possible.

And I’m glad I didn’t switch because then I stumbled upon Jujutsu.

Taskcluster Github is the Taskcluster service responsible for kick starting tasks on Github repositories. At a high level:

1. You install a Taskcluster app from the Github marketplace.
2. This app sends webhooks to the Github service.
3. Upon receiving a webhook, the Github service processes your repository’s .taskcluster.yml file.
4. The Github service schedules tasks (if any) and updates the Github checks suite, or comments on your push / pull-request if there is an error.

While the service itself is relatively simple, testing it locally can be a pain! One approach might be to try and synthesize Github’s webhook events, and then intercept the network requests that the Github service makes in response. But this is tricky to do, and without actually seeing the results in a proper Github repo, it’s hard to be sure that your changes are working as intended.

Ideally you would have a real repo, with a development version of the app listed in the Github Marketplace, hooked up to a Taskcluster Github service running on your local machine. This way you could trigger webhooks by performing real actions in your repo (such as opening a pull-request). Better yet, you could see exactly how your Github service changes react!

Thanks to a lot of great work from Yarik, this is easier than ever and is all documented (or linked to) from this page. If you are already familiar with Taskcluster development, or enjoy figuring things out yourself, you may wish to skip this post and read the docs instead. But if you are a Taskcluster newbie, and would appreciate some hand holding, follow along for a step by step tutorial on how to work on and test Taskcluster Github!

Introducing taskgraph --diff to help validate your task configuration changes.

Last time we looked at some ways reviewers can keep the review process moving efficiently. This week, let’s put on our author hats and do the same thing.

In the next two posts we will examine the etiquette of using Phabricator. This post will examine tips from the reviewer’s perspective, and next week will focus on the author’s point of view. While the social aspects of etiquette are incredibly important, we should all be polite and considerate, these posts will focus more on the mechanics of using Phabricator. In other words, how to make the review process as smooth as possible without wasting anyone’s time.

Let’s dig in!

If it ain’t broke don’t fix it.

This old addage is valuable advice that has been passed down through generations. But it hasn’t stopped these people from rewriting command line tools perfected 30+ years ago in Rust.

This week we’ll take a quick look at exa, a replacement for ls. So why should you ignore the wise advice from the addage and replace ls? Because there are marginal improvements to be had, duh! Although the improvements in this case are far from marginal.

Following up last week’s post on some mach try fundamentals, I figured it would be worth posting some actual concrete tips and tricks. So without further ado, here are some things you can do with ./mach try you may not have known about in rapid fire format.

There is a lot of confusion around mach try. People frequently ask “How do I get task X in mach try fuzzy?” or “How can I avoid getting backed out?”. This post is not so much a tip, rather an explanation around how mach try works and its relationship to the CI system (taskgraph). Armed with this knowledge, I hope you’ll be able to use mach try a little more effectively.

Mozilla developers often need to juggle multiple build configurations in their day to day work. Strategies to manage this sometimes include complex shell scripting built into their mozconfig, or a topsrcdir littered with mozconfig-* files and then calls to the build system like MOZCONFIG=mozconfig-debug ./mach build. But there’s another method (which is basically just a variant on the latter), that might help make managing mozconfigs a teensy bit easier: mozconfigwrapper.

In the interest of not documenting things in blog posts (and because I’m short on time this morning), I invite you to read the README file of the repo for installation and usage instructions. Please file issues and don’t hesitate to reach out if the README is not clear or you have any problems.

Have you ever submitted a patch to Phabricator only to have reviewbot reveal dozens of lint errors all over? Or worse yet, have you landed before reviewbot had a chance to analyze your patch and been backed out over lint failures? If so fear not, we’ve all been there. Still, it’s hard not to feel a little embarrassed when it happens. Luckily for you, it’s pretty easy to eliminate the possibility of it ever happening again!