Earlier this week, I landed some changes to the Firefox development environment that aggressively make mach prompt to run mach mercurial-setup. Full details in bug 1182677.

As expected, the change resulted in a fair amount of whining and bemoaning among various Firefox developers. I wanted to take some time to explain why we moved forward, even though we knew not everyone would like the feature.

My official job title at Mozilla is Developer Productivity Engineer. My job is to make you do your job better.

I've been an employee at Mozilla for four years and in that time I've witnessed a surprising lack of understanding around version control tools. (I don't think Mozilla is significantly different from most other companies here.) I find that a significant number of people are practicing sub-optimal version control workflows because they don't know any better (common) or because they are unwilling to change from learned habits.

Furthermore, Mercurial is a highly customizable tool. A lot of Mozillians have spent a lot of time developing useful extensions to Mercurial that enable Mozillians to use Mercurial more effectively and to thus become more productive. The latest epic time-saving hack is Nick Alexander's work to make Fennec build 80% faster by having deep integration with version control.

mach mercurial-setup is almost two years old. Yet, when assisting my fellow Mozillians with Mercurial issues, my "have you run mach mercurial-setup?" question is still often met with blank stares followed by "wait, there's a mach mercurial-setup?!" What's even more frustrating is people wrongly believing that Mercurial can't do things like rebasing and then spreading misinformation about the lackings of Mercurial. (Mercurial has many advanced features disabled out of the box so new users don't footgun themselves.)

Just like Firefox would be irrelevant if it didn't have millions of users, your awesome tool is mostly irrelevant if you are its only user. That's why when I hear of someone say they created an amazing tool for themselves or modified a third party tool without sending the improvements upstream, my blood pressure rises a little. It rises because here this person did something awesome and they or some limited subset of people who happened to be following the person on Twitter or reading their blog at that point in time managed to a) know about the tool b) take the effort to install it. The uptake rate is insanely low and return on investment for that tool is low. It results in duplication of effort. I find this painfully frustrating because I want everyone to have easy access to the best tools available. This requires that tools are well advertised and easy to install and use.

The primary goal of mach mercurial-setup is to make it super easy for anyone to have an optimal Mercurial experience. It was apparent to me that despite mach mercurial-setup existing, numerous people didn't know it existed or weren't using it. Your awesome tool isn't very awesome unless people are using it. And a lot of the awesome tools people have built around Mercurial at Mozilla weren't being utilized and lots of productivity wins were thus being unrealized. Forcefully pushing mach mercurial-setup onto people is thus an attempt to unlock unrealized productivity wins and to make people happier about the state of their tools.

I'm not thrilled that mach's prompting to run mach mercurial-setup is as disruptive as it is. It's bad user experience. I know better. But, (and this is explained somewhat in the bug), other solutions are more complicated and have other gotchas. The current, invasive implementation was the easiest to implement and has the biggest bang for the buck in terms of adoption. We knew people would complain about it. But from my perspective, it was do this or do nothing. And nothing hadn't been very effective. So we did something.

There has been lots of feedback about the change this week. Most surprising to me is the general sentiment of "I don't want something automatically changing my hgrc file." I find this surprising because mach mercurial-setup puts the user firmly in control by prompting before doing anything, thus respecting user choice and avoiding gotchas and unwanted changes. It's clear this property needs to be advertised a bit more so people aren't scared to run mach mercurial-setup and don't spread fear, uncertainty, and doubt about the tool to others. (I also find it somewhat surprising people would think this in the first place: I'd like to think we'd implicitly trust most Mozillians to implement tools that respect user choice and don't do malicious things.)

Like all software, things can and will change. The user experience of this new feature isn't terrific. We'll iterate on it. If you want to help enact change, please file a bug in Core :: mach (for now) and we'll go from there.

Thank you for your patience and your understanding.