Thursday, April 30, 2015

rustfmt - call for contributions

I've been experimenting with a rustfmt tool for a while now. Its finally in working shape (though still very, very rough) and I'd love some help on making it awesome.

rustfmt is a reformatting tool for Rust code. The idea is that it takes your code, tidies it up, and makes sure it conforms to a set of style guidelines. There are similar tools for C++ (clang format), Go (gofmt), and many other languages. Its a really useful tool to have for a language, since it makes it easy to adhere to style guidelines and allows for mass changes when guidelines change, thus making it possible to actually change the guidelines as needed.

Eventually I would like rustfmt to do lots of cool stuff like changing glob imports to list imports, or emit refactoring scripts to rename variables to adhere to naming conventions. In the meantime, there are lots of interesting questions about how to lay out things like function declarations and match expressions.

My approach to rustfmt is very incremental. It is usable now and gives good results, but it only touches a tiny subset of language items, for example function definitions and calls, and string literals. It preserves code elsewhere. This makes it immediately useful.

I have managed to run it on several crates (or parts of crates) in the rust distro. It also bootstraps, i.e., you can rustfmt on rustfmt before every check-in, in fact this is part of the test suite.

It would be really useful to have people running this tool on their own code or on other crates in the rust distro, and filing issues and/or test cases where things go wrong. This should actually be a useful tool to run, not just a chore, and will get more useful with time.

It's a great project to hack on - you'll learn a fair bit about the Rust compiler's frontend and get a great understanding of more corners of the language than you'll ever want to know about. It's early days too, so there is plenty of scope for having a big impact on the project. I find it a lot of fun too! Just please forgive some of the hackey code that I've already written.

Here is the rustfmt repo on GitHub. I just added a bunch of information to the repo readme which should help new contributors. Please let me know if there is other information that should go in there. I've also created some good issues for new contributors. If you'd like to help out and need help, please ping me on irc (I'm nrc).

Monday, April 13, 2015

Contributing to Rust

I wrote a few things about contributing to Rust. What with the imminent 1.0 release, now is a great time to learn more about Rust and contribute code, tests, or docs to Rust itself or a bunch of other exciting projects.

The main thing I wanted to do was make it easy to find issues to work on. I also stuck in a few links to various things that new contributors should find useful.

I hope it is useful, and feel free to ping me (nrc in #rust-internals) if you want more info.

Sunday, April 12, 2015

New tutorial - arrays and vectors in Rust

I've just put up a new tutorial on Rust for C++ programmers: arrays and vectors. This covers everything you might need to know about array-like sequences in Rust (well, not everything, but at least some of the things).

As well as the basics on arrays, slices, and vectors (Vec), I dive into the differences in representing arrays in Rust compared with C/C++, describe how to use Rust's indexing syntax with your own collection types, and touch on some aspects of dynamically sized types (DSTs) and fat pointers in Rust.

Friday, April 03, 2015

Graphs in Rust

Graphs are a bit awkward to construct in Rust because of Rust's stringent lifetime and mutability requirements. Graphs of objects are very common in OO programming. In this tutorial I'm going to go over a few different approaches to implementation. My preferred approach uses arena allocation and makes slightly advanced use of explicit lifetimes. I'll finish up by discussing a few potential Rust features which would make using such an approach easier.

There are essentially two orthogonal problems: how to handle the lifetime of the graph and how to handle it's mutability.

The first problem essentially boils down to what kind of pointer to use to point to other nodes in the graph. Since graph-like data structures are recursive (the types are recursive, even if the data is not) we are forced to use pointers of some kind rather than have a totally value-based structure. Since graphs can be cyclic, and ownership in Rust cannot be cyclic, we cannot use Box<Node> as our pointer type (as we might do for tree-like data structures or linked lists).

No graph is truly immutable. Because there may be cycles, the graph cannot be created in a single statement. Thus, at the very least, the graph must be mutable during its initialisation phase. The usual invariant in Rust is that all pointers must either be unique or immutable. Graph edges must be mutable (at least during initialisation) and there can be more than one edge into any node, thus no edges are guaranteed to be unique. So we're going to have to do something a little bit advanced to handle mutability.


Read the full tutorial, with examples. There's also some discussion of potential language improvements in Rust to make dealing with graphs easier.