Tracking Issue for RFC 3484: Unsafe Extern Blocks

[traviscross]

This is a tracking issue for the RFC 3484: Unsafe Extern Blocks

• Unsafe Extern Blocks rfcs#3484

The feature gate for the issue is #![feature(unsafe_extern)].

About tracking issues

Tracking issues are used to record the overall progress of implementation. They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions. A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature. Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Accept the RFC.
  • Unsafe Extern Blocks rfcs#3484
• Add the next edition to rustc.
• Implement in nightly Rust 2027.
• Implement migration lints.
• Add documentation to the dev guide.
  • See the instructions.
• Add documentation to the reference.
  • See the instructions.
• Add documentation to the edition guide.
• Add formatting for new syntax to the style guide.
  • See the nightly style procedure.
• Ensure ready for Rust 2027 stabilization.

Unresolved Questions

• Extern declarations are actually always unsafe and able to cause UB regardless of edition. This RFC doesn't have a specific answer on how to improve pre-2027 code.
  • could use attributes

Implementation history

• Unsafe extern blocks #124482
• Add new safety enum for inner extern items #124455
• Rename Unsafe to Safety #125077
• Add "better" edition handling on lint-docs tool #125522

cc @Lokathor @spastorino

[oli-obk]

I have been reviewing some work (and the required refactorings), and the refactorings need refactorings of their own (not sure how many layers of turtles are needed, but it's not all the way down) 😓

The only way to get it done in time is to not do refactorings before, but just leave FIXMEs, which doesn't sit right with me. So:

let's not do this for the 2024 edition, but jump straight into implementing the 2027 edition