Dipping my toes in the Servo waters

I’m very interested in Rust and Servo, and have been following their development closely. I wanted to actually do some coding in Rust, so I decided to start making small contributions to Servo.

At this point I have landed two changes in the tree — one to add very basic memory measurements for Linux, and the other for Mac — and I thought it might be interesting for people to hear about the basics of contributing. So here’s a collection of impressions and thoughts in no particular order.

Getting the code and building Servo was amazingly easy. The instructions actually worked first time on both Ubuntu and Mac! Basically it’s just apt-get install (on Ubuntu) or port install (on Mac), git clone, configure, and make. The configure step takes a while because it downloads an appropriate version of Rust, but that’s fine; I was expecting to have to install the appropriate version of Rust first so I was pleasantly surprised.

Once you build it, Servo is very bare-boned. Here’s a screenshot.


There is no address bar, or menu bar, or chrome of any kind. You simply choose which page you want to display from the command line when you start Servo. The memory profiling I implemented is enabled by using the -m option, which causes memory measurements to be periodically printed to the console.

Programming in Rust is interesting. I’m not the first person to observe that, compared to C++, it takes longer to get your code past the compiler, but it’s more likely to to work once you do. It reminds me a bit of my years programming in Mercury (imagine Haskell, but strict, and with a Prolog ancestry). Discriminated unions, pattern matching, etc. In particular, you have to provide code to handle all the error cases in place. Good stuff, in my opinion.

One thing I didn’t expect but makes sense in hindsight: Servo has seg faulted for me a few times. Rust is memory-safe, and so shouldn’t crash like this. But Servo relies on numerous libraries written in C and/or C++, and that’s where the crashes originated.

The Rust docs are a mixed bag. Libraries are pretty well-documented, but I haven’t seen a general language guide that really leaves me feeling like I understand a decent fraction of the language. (Most recently I read Rust By Example.) This is meant to be an observation rather than a complaint; I know that it’s a pre-1.0 language, and I’m aware that Steve Klabnik is now being paid by Mozilla to actively improve the docs, and I look forward to those improvements.

The spotty documentation isn’t such a problem, though, because the people in the #rust and #servo IRC channels are fantastic. When I learned Python last year I found that simply typing “how to do X in Python” into Google almost always leads to a Stack Overflow page with a good answer. That’s not the case for Rust, because it’s too new, but the IRC channels are almost as good.

The code is hosted on GitHub, and the project uses a typical pull request model. I’m not a particularly big fan of git — to me it feels like a Swiss Army light-sabre with a thousand buttons on the handle, and I’m confident using about ten of those buttons. And I’m also not a fan of major Mozilla projects being hosted on GitHub… but that’s a discussion for another time. Nonetheless, I’m sufficiently used to the GitHub workflow from working on pdf.js that this side of things has been quite straightforward.

Overall, it’s been quite a pleasant experience, and I look forward to gradually helping build up the memory profiling infrastructure over time.

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