Implement restrictions, prepare for stabilization (original) (raw)

Summary

RFC 3323 will be implemented and feature-complete, with all syntax questions resolved. The features will be prepared for stabilization.

Motivation

The RFC for restrictions was accepted over two years ago, but the pull request implementing it has been stalled for a long time for a variety of reasons. Implementing the feature will permit testing, feedback, and stabilization.

The status quo

Sealed traits are a common pattern in Rust, but are not currently supported by the language itself. Instead, they are implemented using a combination of visibility modifiers and nested modules. Fields with restricted mutability are currently only possible with getters and setters, setting aside (ab)using Deref implementations.

More details are available in the RFC.

The next 6 months

The accepted restrictions RFC represents the end goal of this project goal. All unresolved questions should be discussed and resolved, with the two features (impl_restrictions andmut_restrictions) being ready for stabilization. Future possibilities are likely considered at a high level, but are not the focus of this project goal.

Ownership and team asks

Owner: Jacob Pratt

Definitions

Definitions for terms used above:

• Discussion and moral support is the lowest level offering, basically committing the team to nothing but good vibes and general support for this endeavor.
• Author RFC and Implementation means actually writing the code, document, whatever.
• Design meeting means holding a synchronous meeting to review a proposal and provide feedback (no decision expected).
• RFC decisions means reviewing an RFC and deciding whether to accept.
• Org decisions means reaching a decision on an organizational or policy matter.
• Secondary review of an RFC means that the team is "tangentially" involved in the RFC and should be expected to briefly review.
• Stabilizations means reviewing a stabilization and report and deciding whether to stabilize.
• Standard reviews refers to reviews for PRs against the repository; these PRs are not expected to be unduly large or complicated.
• Prioritized nominations refers to prioritized lang-team response to nominated issues, with the expectation that there will be some response from the next weekly triage meeting.
• Dedicated review means identifying an individual (or group of individuals) who will review the changes, as they're expected to require significant context.
• Other kinds of decisions:
  • Lang team experiments are used to add nightly features that do not yet have an RFC. They are limited to trusted contributors and are used to resolve design details such that an RFC can be written.
  • Compiler Major Change Proposal (MCP) is used to propose a 'larger than average' change and get feedback from the compiler team.
  • Library API Change Proposal (ACP) describes a change to the standard library.

Frequently asked questions

Isn't the syntax already decided?

While the RFC was accepted without this being an unresolved question (aside from a simpler syntax for common cases), I believe that an attribute-based syntax such as #[restrict(impl(crate))] may be, but is not necessarily, favorable to the syntax in the RFC. This is because it is backwards-compatible with all existing macros and prevents nontrivial additions to the width of code.