Rust Lang Roadmap for 2024

Apr. 4, 2022 · Josh Triplett, Niko Matsakis on behalf of The Rust Lang Team

Note: this blog post is a snapshot of the living roadmap at https://lang-team.rust-lang.org/roadmaps/roadmap-2024.html. Subsequent changes may occur in that version, but not in this blog post. Please see that page for the most up-to-date version.

Lang Team Roadmap 2024

Rust 1.0 was released in 2015. Since that time, we've seen Rust grow from a small language used for a handful of prominent projects into a mainstay in use at virtually every major tech company.

As we work towards Rust 2024, it's natural to ask what's next for the language. This roadmap provides insight into that question by describing what we, as members of the lang team with input from other Rust teams, would like to prioritize.

We have two goals with this roadmap:

  • to give people a sense for what to expect in Rust over the next few years;
  • for those who would like to contribute to Rust, to help provide "starting points" for how to get involved, and a sense for what kind of projects we are looking for.

Also see the Rust Compiler Ambitions for 2022, for plans from the Rust Compiler team, and watch the Inside Rust blog for the upcoming roadmap from the Rust Library team.

Rust 2024: scaling empowerment

Rust's goal is to empower everyone to build reliable and efficient software. Success requires not only designing and implementing a great language with great libraries and great tools, but also maintaining a great and supportive community.

Our focus for Rust 2024 is to scale empowerment in many different ways. As we grow, we face increasing challenges in how we can scale the ways in which we empower people to an increasing number of people. This roadmap presents three general themes we plan to focus on:

  • Flatten the (learning) curve: scaling to new users and new use cases
    • Make Rust more accessible to new and existing users alike, and make solving hard problems easier.
  • Help Rust's users help each other: scaling the ecosystem
    • Empower library authors so they can---in turn---empower their users.
  • Help the Rust project scale: scaling the project
    • Develop processes to scale to the needs and use cases of a growing number of users; evaluate and finish projects we've started.

For each theme, we'll describe our goals for Rust 2024, and give a few examples of the kinds of things that we're working on right now, as well as the kinds of things we would like to do over the next few years.

This roadmap is a starting point. Our intent is to highlight those areas that will have the biggest impact on Rust's success. Specific examples will change over time, whether because they're finished or because new proposals arise. As 2023 approaches, we will revisit these themes to see how much progress we have made, and whether we wish to adjust the list.

Theme: Flatten the (learning) curve

The vision

Thanks to a consistent focus on ergonomics, Rust has become considerably easier to use over the last few years. Companies building large teams of Rust users report that the typical onboarding time for a Rust engineer is around 3-6 months. Once folks learn Rust, they typically love it. Even so, many people report a sense of high "cognitive overhead" in using it, and "learning curve" remains the most common reason not to use Rust. The fact is that, even after you learn how the Rust borrow checker works, there remain a lot of "small details" that you have to get just right to get your Rust program to compile.

For Rust 2024, we will identify and eliminate many of those patterns and idiosyncracies that one must learn to use Rust; our goal is to let you focus squarely on the "inherent complexity" of your problem domain and avoid "accidental complexity" from Rust as much as possible.

Async and embedded Rust are areas of particular interest. We have made a lot of strides to support those areas, and they are growing rapidly. Nonetheless, Rust lacks many core capabilities that would be required to make working in those domains not only possible but straightforward and delightful. For Rust 2024, we will close that gap.

Our plan for achieving this vision is to focus on four high-level goals (in order from broad to precise):

  • More precise analyses, less rigamarole: Make the compiler better able to recognize when code is correct via improvements to the borrow checker, type inference, and so forth. Identify and eliminate "boilerplate" patterns like having to copy-and-paste the same set of where clauses everywhere.
  • Express yourself more easily: Where necessary, extend the language so you can express what you want your code to do more directly. In some cases this takes the form of syntactic sugar (such as let-else) but in other cases it may mean extending the type system to be able to describe new patterns (such as generic associated types).
  • Improve async support: Extend our async-await support beyond the current "MVP" to include features like async fns in traits, async drop, and other features needed to support the async vision document roadmap.
  • Make dyn Trait more usable: Broaden the set of traits that can be used with dyn and make working with dyn closer to working with generics.

How you can help

Join the rust-lang Zulip, and either start a thread in the #t-lang/roadmap-2024 stream, or send a private message to nikomatsakis if you'd like to discuss privately first.

The plan (so far)

Current active initiatives in each category include:

  • More precise analyses, less rigamarole:
    • Non-lexical lifetimes were a big stride forward, but the polonius project promises to improve the borrow check's precision even more.
    • Implied bounds promise to remove a lot of copy-and-pasting of where clauses.
  • Express yourself more easily:
    • let-else directly express the "match this variant or return/continue/etc" pattern.
    • let-chains allow you to express iterative refinement with a series of pattern-matches and conditionals
    • "Type alias" impl Trait permits APIs to name previously unnameable types. This is part of a larger effort to expand impl Trait.
    • Generic associated types allow traits to express a number of patterns (like "iterable") that the current trait system cannot handle. They are a particularly important foundational piece for async programming.
  • Improve async support:
    • We are working to support async fns in traits, including both static dispatch and dyn dispatch.
  • Make dyn Trait more usable:

Looking forward

Looking beyond the initiatives that are in progress, there's a lot of room for more improvement. Here are some other ideas we'd like to see. For many of these ideas, the main thing they need is someone to own the design! If you might be interested in giving that a try, come to #t-lang/roadmap-2024 to discuss, or send a private message to nikomatsakis.

  • More precise analyses, less rigamarole:
    • Deref patterns: Permit matching types with patterns they can dereference to, such as matching a String with a "str".
    • Perfect derive: determine the precise conditions for generic type parameters based on the types of a struct fields. For instance, #[derive(Clone)] struct MyStruct(Rc<T>) would not require T: Clone, because Rc<T> can be cloned without it.
    • Autoref, operators, and clones: Generic methods that operate on references sometimes necessitate types like &u32; since u32 is Copy, we could automatically make it a reference. We've historically had some hesitance to add more reference-producing operations, because it can lead to types the user doesn't expect (such as &&&str). We have some ideas to simplify those cases and avoid unnecessary double-references.
  • Express yourself more easily:
    • Generators, allowing users to write iterators (async and otherwise) using custom syntax.
  • Improve async support:
    • After adding async fn in traits, we intend to add support for async drop, async closures, and potentially other features.
  • Make dyn Trait more usable:
    • Make more patterns "object safe" and thus usable in dyn Trait objects, including passing self by value and handling impl Trait in argument position (see this post for more information).

Theme: Help users help each other

The vision

Rust's combination of ownership and borrowing, low-level systems control, and powerful extensibility mechanisms like procedural macros makes it a great language for writing libraries. And, thanks to Cargo, using a library in your program only takes a few lines of code. Nonetheless, there are a number of things that library authors can't do, or can't do easily -- for example, they can't control the error messages you see or deploy an "unstable" feature that requires special opt-in to use. For Rust 2024, we want to build features that empower library authors to better serve their users, either by helping to manage the feature lifecycle or by expanding the capabilities of what a library can do.

We encourage people to experiment and explore in the library ecosystem, building new functionality for people to use. Sometimes, that new functionality becomes a foundation for others to build on, and standardizing it simplifies further development atop it, letting the cycle continue at another level. However, some aspects of the Rust language (notably coherence) make it harder to extend the Rust standard library or well-established crates from separate libraries, discouraging experimentation. Other features (such as aspects of method resolution) make it hard to promote best-in-class functionality into the standard library or into well-established crates without breaking users of the crates that first developed that functionality. For Rust 2024, we want to pursue changes that enable more exploration in the ecosystem, and enable stable migration of code from the ecosystem into the standard library.

Our plan for achieving this vision is to focus on four categories of work:

  • Feature lifecycle: Help library authors support features as they move from experimental to finalized. Help library authors manage their development lifecycle and evolution.
  • Richer abstractions: Extend the language to let library authors express richer abstractions.
  • Custom developer experience: Permit library authors can tailor the developer experience, for example by tailoring the error messages a user gets when traits are not implemented or introducing custom lints.
  • Interoperability: The library ecosystem can easily coordinate, making libraries work together without tying them together. Library authors can write code that is portable across many environments or specific to one, as they please.

How you can help

Join the rust-lang Zulip, and either start a thread in the #t-lang/roadmap-2024 stream, or send a private message to Josh Triplett if you'd like to discuss privately first.

The plan (so far)

Current active initiatives in each category include:

  • Feature lifecycle:
  • Richer abstractions:
  • Custom developer experience:
    • We are not currently doing any coordinated initiatives here, though there are ongoing efforts that help lay groundwork for this.
  • Interoperability:

Looking forward

Looking beyond the initiatives that are in progress, there's a lot of room for more improvement. Here are some other ideas we'd like to see. For many of these ideas, the main thing they need is someone to own the design! If you might be interested in giving that a try, come to #t-lang/roadmap-2024 to discuss, or send a private message to Josh Triplett.

  • Feature lifecycle:
    • All ecosystem crates can have "release trains", with the equivalent of "nightly features" that require a stability opt-ins. Top-level crates retain control over whether any of their dependencies may use nightly features.
  • Richer abstractions:
    • Allow libraries to implement the Fn traits to define callable objects.
    • Variadic tuples and variadic generics would address a common pain point of "implement this trait for tuples of any arity".
  • Custom developer experience:
    • Allow libraries to provide custom lints for their users.
    • Allow libraries to control or customize Rust diagnostics, especially for trait resolution failures.
  • Interoperability:
    • Revive the stalled portability lint or pursue an alternative design (a recent suggestion is that the "platform" might be a global service, similar to RFC 2492, permitting one to use where clauses to designate portable code)
    • The coherence rules make it hard to implement interoperability traits; we should find a way to lift this restriction, while preserving coherence's key benefits.
    • Adopt a standard way to write performance benchmarks (perhaps simply adopt criterion officially).
    • Better support for dynamic linking, with richer and safer types than the C ABI. For instance, implement an extern "safe" providing a subset of Rust's rich types.

Theme: Help the Rust project scale

The vision

The Rust repo is a blizzard of activity. This is great, but it can be overwhelming, particularly if you are trying to figure out the status of some particular thing that you are interested in or would like to contribute to.

To ship Rust 2024 and make Rust all that it can be, we need a system that makes it easy for people to find out what's going on and how they can help. We want to scale our language development through delegation, empowering developers to own and drive the work that they are passionate about. Lang team liaisons and frequent lang team check-in will help ensure quality, stability, and overall coherence. The team itself will have a clear "path to membership" that helps us to maintain our membership and make sure we have the expertise we need.

Our plan for achieving this vision is to focus on four categories of work:

  • See the status at a glance: We want it to be easy to identify what things the lang-team is actively working on and how far those designs have come. We want every tracking issue to clearly identify what "next steps" are needed to push that particular feature over the finish line and make sure that those steps are clearly documented for would-be contributors.
  • Clear owners and clear communication: Rust operates by consensus, but that doesn't mean that everybody has to know all the details of everything. We need a system that has clear owners for the work to be done, and ideally, owners that are not on the lang team. Simply dividing work though can lead to conflicts later on, so we also need frequent communication and updates to ensure that everyone is keeping abreast of the overall direction things are going, and to surface concerns early.
  • Efficient, open processes with tooling support: We are always looking for ways to improve how we operate to help us stay on top of what is going on in the Rust project and to reach conclusions more quickly. One thing we've noticed is that processes that are supported by bots or other tooling tend to work much better.

How you can help

Join the rust-lang Zulip, and either start a thread in the #t-lang/roadmap-2024 stream, or send a private message to Josh Triplett and nikomatsakis if you'd like to discuss privately first.

The plan (so far)

Current active initiatives in each category include:

  • See the status at a glance:
    • The initiative project board tracks all the currently active initiatives that we are focusing on. For each one, it shows their current stage along with their owners and lang-team liaisons.
    • During the backlog bonanza meetings, we are going through each older tracking issue and identifying what kinds of work is needed to move it forward (needs a summary, needs design work, etc).
    • We're taking the time to stabilize features that people are using, and remove incomplete features as well as features people are not using, with the eventual goal of treating everything open as "in-flight" rather than "unknown". We will also reduce the total number of in-flight features.
  • Clear owners and clear communication:
    • The initiative system assigns each task an owner, who drives the design, as well as a lang-team liaison, who helps ensure alignment with the team. More work is needed to get this system up and running smoothly.
    • We are launching a formality team that will take ownership of ensuring Rust's type soundness and diving into the details. This will help to grow the set of people with expertise in that area while also allowing the main lang team to consult as needed.
  • Efficient, open processes with tooling support:
    • We have designed a new consensus decision process that is designed to overcome some of the shortcomings we've seen with rfcbot; it needs to be implemented. This will help us make easily reversible decisions easier, enable more experimentation, make it smoother to raise and resolve concerns, and keep track of potential issues from proposal through to stabilization

Looking forward

Looking beyond the initiatives that are in progress, there's a lot of room for more improvement. Here are some other ideas we'd like to see. If you might be interested in giving that a try, come to #t-lang/roadmap-2024 to discuss, or send a private message to Josh Triplett and nikomatsakis.

  • See the status at a glance:
    • Find ways to integrate the older tracking issues with active initiatives; reduce the manual updates required to keep the project board in sync.
    • Improve the visualization of projects and blockers to something more compelling and easier to follow.
  • Clear owners and clear communication:
    • Beyond the type system, there are other areas where forming specialized teams could be useful.
  • Efficient, open processes with tooling support:
    • Generally improve rustbot to make meetings more efficient.
    • Improve and automate the process of going from initiative proposal to tracked initiative.

Conclusion

We hope that this post has given you a taste for what we plan to focus on over the next few years. If you'd like to help us reach these goals, please get involved! We've listed a number of active initiatives for each point, but we've also included a lot of ideas that are looking for an owner. Whether you prefer to code, design, document, or organize, there's work for you to do. And if the only thing you want to do with Rust 2024 is to use it, we welcome that too. Happy Rust hacking to y'all!