The Rust Libz Blitz

May 5, 2017 · Brian Anderson, David Tolnay, and Aaron Turon

To help bring our 2017 vision for Rust to fruition, the Rust subteams are launching initiatives targeted at specific roadmap goals. This post covers the library team's major initiative: raising a solid core of the Rust crate ecosystem to a consistent level of completeness and quality. This work is guided in part by what we learned in producing the Rust standard library, and will result in a "cookbook" chock full of ready-made examples for common tasks, drawing from a careful selection of Rust crates.

(Also, ICYMI: please participate in the State of Rust survey; even if you don't use Rust, we'd love to hear from you!)

Batteries included?

You can't be productive in a language without libraries that are easy to find and use. Of course, the easiest library to find is the standard library, and many languages have taken a "batteries included" approach that includes APIs for a broad set of tasks directly in the standard library. There's a lot of upside to doing so: it means there's just one place to look for common tasks, with APIs that (hopefully!) cohere across tasks, compatibility across the ecosystem, and a promise of library maintenance. What's not to like?

There's a countervailing mindset which, in its harshest terms, says "the standard library is where code goes to die" (a complaint sometimes heard about batteries-included standard libraries). Because the standard library is coupled to the language itself, it is released at the same frequency as the language is, and making breaking changes means breaking the whole language. For these reasons and others, standard libraries tend to evolve conservatively.

As usual in the Rust world, our goal is to have our cake and eat it too. Can we provide something like a batteries-included experience, without ossifying that code in the standard library? This is a particularly vital question for Rust because, as a community, we are still rapidly exploring and iterating on best practices for ownership-based API design.

The key ingredient to our approach is Cargo, the package manager that shipped with Rust 1.0 and has been improving ever since. Cargo provides a unified dependency and workflow story across the entire Rust ecosystem, and makes adding dependencies a painless and relatively low-risk proposition. The ability to share code with ease is a powerful change to the character of, and audience for, traditional systems programming tasks.

Because of Cargo, we can "include batteries" without literally putting them into the standard library; pulling in other crates is nearly as easy as using the standard library (and will likely get even easier this year). But to capitalize on this ability to the fullest, we need to have excellent libraries. Our mission for 2017 is to ensure that crates are available for a wide swath of common tasks and that they are discoverable, cohesive, featureful, and well-documented.

The Rust Libz Blitz

Fortunately, while the standard library has stayed small and focused, the ecosystem has been growing at breakneck pace. So the challenge here isn't greenfield library work. It's more a question of: how can the Rust community work in a focused way to polish, consolidate, and surface a core set of libraries for essential tasks? Our answer is the Rust Libz Blitz.

The basic idea is to:

  • Collectively review a few crates at a time in a shared forum. The review draws in part from a set of API guidelines.
  • Every two weeks, hold a library team meeting focused on open questions around one of these crates, with the author in attendance.
  • Push this feedback onto a tracking issue for the crate, and point the Rust community there to help shoulder the burden of making improvements.
  • Write up entries for each crate in a new Rust Cookbook, which will make it easy to discover the crate and jump into using it.

The Rust library team has been quietly engaging in this process already for the past couple of months, to sort out the kinks. But now, we want to open it up to the whole Rust community. In the rest of the post, we'll dive a bit more deeply into the mechanics and goals of this process.

Rust standards of quality

In all the work on the standard library, we have gained a sense of what makes Rust APIs great: principles like "make performance characteristics clear" and "use ownership to encapsulate invariants"; consistent naming conventions like mut, ref, as, into, that let users intuit what they don't know from what they do; small details of presentation that add up, like consistently documenting possible error cases in a dedicated "Errors" section; and so many more factors to consider when publishing Rust crates.

In 2017 we plan to apply the principles behind the design of std to an ever-widening foundation of critical Rust libraries. Along the way we will document what we learn about Rust library design.

The product of this process will be a mature core of libraries together with a set of API guidelines that Rust authors can follow to gain insight into the design of Rust and level up crates of their own interest. Today those guidelines are in a very early state, but give you a sense of where we are headed with this effort. Take a look and file issues where things are unclear or missing!

Rust standards of documentation

We recently ran a small survey to see what Rust programmers care most about when evaluating a crate. The most common criterion, by far, was documentation. So a big part of the Libz Blitz process will be evaluating and improving the documentation of the targeted crates, which will supplement ongoing efforts to rewrite the Rust book and provide comprehensive examples for the standard library. The API guidelines contain a section dedicated to great documentation, and we aim for a consistent, easy to navigate docs experience across all of the core crates.

Beyond documentation within the crates themselves (which tends to be more of the "reference" flavor), we are also starting a Rust Cookbook, which will be organized around problems you want to solve, and provide quick, concrete example code you can drop directly into your project, drawing from a variety of crates (including the standard library). Examples like these are one of the most useful tools for quickly getting productive with a library, and collecting them all in one place, organized by problem, will help get us to a "batteries included" experience when working with Rust.

Part of the work done in the Libz Blitz for each crate will be identifying the key problem statements the crate is trying to address, and adding strong examples for each to the cookbook.

Rust standards of discoverability

Perhaps the biggest downside to having a small standard library is the problem of discoverability: when a Rust programmer needs to take on a task not covered by the standard library, how do they figure out where to look?

The cookbook mentioned above will undoubtedly become a major part of our answer. But at the same time, we want to ensure that there's space for new crates to emerge, and that people can easily find crates beyond the most common problem areas. To that end, we're attacking discoverability head on, by rolling out badges for various quality indicators on, and greatly improving the default ranking of results (a design debated vigorously through an RFC). There's plenty of room for more work here, so if you have ideas about further improving discoverability on, please start a thread!

Rust standards of community

We have some idea of what goes into publishing exceptional Rust crates, but the Rust library team is not the sole authority of Rust API design—the Rust crate ecosystem is created by all of us together and there are many lessons yet to learn. In recognition of that, the library team is architecting our efforts to be as welcoming and inclusive as we can.

We will kick off forum discussions for evaluating existing crates that we believe are vital to set on a path toward stability, and which mostly need polish-level work to get there. These evaluations will be collaborative and intended for public commentary. They are designed to identify any issues separating the crate from "1.0" status (in terms of quality and API stability, as well as literal version number). Issues may include poor adherence to Rust API design principles, substantial missing functionality, planned API refactors, incomplete documentation, or any number of unique circumstances.

We'll have a small handful of such evaluations going on in parallel. Every two weeks, the library team will take up one of the evaluations for discussion in our regular video conference, which will be recorded and made available on Air Mozilla and the Rust YouTube channel. One goal of these meetings will be to plan out a roadmap for stabilizing the crate in question. The other goal will be to identify any lessons to be learned from the crate and distill those into broadly applicable API guidelines.

We will have a rotating band of guests (including the crate authors) at the video conferences by invitation, in order to strengthen the bonds between the Rust team and the authors of the Rust ecosystem, and to foster shared values among the same.

Based on the evaluations and library team review, we will file issues that we believe are important to resolve before producing a stable release of the crate. We are counting on many of these issues being amenable to casual contributions.

Here are the issues that arose from the very simple byteorder crate (all resolved now):

Beyond byteorder we've already worked this process for several other simple crates to get a feel for it: bitflags, tempdir, flate2, and lazy_static. Even these, the most basic of crates, have some work left to do but you can expect them to have "1.0" releases soon. As the crates under evaluation grow in scope, presumably the tasks that arise will grow as well.

What crates are we going to focus on?

Rust has some amazing libraries in the works: things like tokio which is a really fast asynchronous I/O framework; like diesel, a really fast library for interacting with database tables; and like rocket, a really fast web framework.

We are not going to be touching them.

These high-profile libraries are built on dozens of smaller crates that perform crucial functions across the ecosystem: random number generation, memory mapping, compression, and so much more. We need to polish off the lower layers of the Rust stack so that those high-level libraries have a stable foundation to build on.

Focusing on these lower layers is not only a practical consideration but a technical one—a crate should not be stable until its public dependencies are stable. Consider what it would mean for a hypothetical diesel 1.0 to export a function returning a type from a still-rapidly-developed uuid 0.5. Before long it would be incompatible with other libraries using newer versions of uuid.

Furthermore, many of these high-level libraries are very much undergoing their own rapid development, with their own strong leadership. We don't want to impose on those crates' authors' abilities to experiment with their designs by pressuring them to declare crates stable before they are ready. Those libraries will mature in time.

But there are many foundational libraries that have reached relative stability, and are in some cases functionally complete and being widely used in production. Some need little work to put them across the finish line. Some, like the rand crate, are widely used but known to have unsatisfactory designs. We want to finally put those crates to bed.

We are currently drawing this list of foundational crates by combining dependency data, various existing curated crate listings, and good old gut feeling. The exact list is definitely up for debate, and we hope that the broader community will also apply this process completely independently to crates the libs team won't have time to discuss.

How can I help?

We're glad you asked! Creating a solid core of libraries for a young language is not the work of a single person or team—it is the work of the entire community. The central point of coordination is a thread on the Rust internals forum. Read that thread for all the dirty details about what we're doing, and for ongoing opportunities to get involved.

Roles that need your help:

  • Crate lead. Each crate needs a volunteer to lead the evaluation effort. That entails starting up a thread, breaking up the evaluation work into small work items that can be taken on by others in the community, keeping the discussion moving in productive directions, making sure the evaluation is completed on time, presenting the results at the libs team meeting, and, finally, filing discrete, actionable issues on everything raised, and funneling them to TWiR.

    Anyone can be a crate lead, but it's a substantial commitment and is largely about organization, communication, and consensus, and requires presenting to the libs team in a video meeting.

  • Crate evaluator. This is the preliminary work of comparing a crate to the API guidelines, identifying deficiencies, and raising observations about API design that may impact the guidelines. It will often require working with the crate author to understand a crate's known shortcomings.

    Each evaluation will be published to the coordination thread, providing an opportunity for general feedback. Open feedback allows for a wide range of voices to be heard and is an important check against design myopia.

    This effort is collaborative and everyone is welcome to participate in this way at any time. The crate lead will help create opportunities to jump in.

  • Documentation slinger. A lot of the work involved in getting a crate up to full quality is improving documentation, including writing up cookbook entries. There will be lots of opportunities for this kind of high value work.

    Everyone is welcome to participate in this way at any time. The crate lead will help create opportunities to jump in.

  • Library hacker. Somebody must do the programming work of resolving the issues on the roadmap to stability for each crate. We expect to produce many discrete work items and that many of them will be accessible to inexperienced Rust programmers.

    Everyone is welcome to participate in this way at any time. The crate lead will help create opportunities to jump in.

  • Library designer. There remain some important libraries that are only lightly maintained but are known to require significant design work (again thinking of rand especially). These will not improve without a dedicated and skilled author to drive them forward. We are going to be looking out for authors with the design skills necessary to fix the problems, and the social skills necessary to navigate the process.

    We will occasionally make pleas for help on specific design matters as they arise.

  • Libs team guest. The library team will spend one of their video meetings reviewing each crate evaluation. We hope that the crate authors will be interested in joining us, sharing their unique expertise, and getting to know the libs team. This kind of interaction creates strong bonds in a way that communicating through text does not. We hope this will foster shared values across the ecosystem, and pave the way for expanding the libs team more formally.

    This will be by invitation and focused on authors with an existing reputation for high quality work and productive collaboration.

  • Crate author. The libs team has some specific functionality and crates it wants to focus on this year. Outside of that, we are hopeful that the process and guidelines we develop will be widely useful and that crate authors will independently seek to evaluate and improve their own crates in similar ways.


Here's the plan:

  • We will directly improve the most important crates you use every day.
  • We will provide crate authors the guidance they need to do the same, in the form of API guidelines.
  • We will create an endless stream of accessible contribution opportunities that directly contribute to key Rust strategic goals.
  • We will produce cohesive documentation on how to use Rust's most foundational crates, in the form of a crate cookbook.
  • We will launch a self-sustaining process of library improvement that can by applied consistently across the entire ecosystem.

Thank you to everyone who has contributed thus far, including Alisha Aneja, Andrew Gallant, Brad Anderson, Charles Chamberlain, Dan Burkert, David Harris, Jan-Erik Rediger, Peter Atashian, Roman Frołow, Sean McArthur, Simon Sapin, Stephan Buys, Steven Fackler, Trent Spice.