Tracking issue for Rust 2024: Match ergonomics rules 1C/2C

[traviscross]

This is a tracking issue for reserving space in match ergonomics in Rust 2024 for RFC 3627 and other proposals for the future of match ergonomics.

Rules

• Rule 1C: When the DBM (default binding mode) is not move (whether or not behind a reference), writing mut, ref, or ref mut on a binding is an error.
• Rule 2C: Reference patterns can only match against references in the scrutinee when the DBM is move.

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

• Implement in nightly Rust 2024 w/migration lints.
  • Match ergonomics 2024: implement mutable by-reference bindings #123080
  • Match ergonomics 2024: Implement eat-one-layer #123512
  • Match ergonomics 2024: let & patterns eat &mut #124567
  • Match ergonomics 2024: mut doesn't reset binding mode #123535
  • Match ergonomics 2024: migration lint #124639
• Stabilize in Rust 2024.
  • Implement edition 2024 match ergonomics restrictions #131381
• Add documentation to the reference.
  • See the instructions.
• Add documentation to the edition guide.
• Ensure ready for Rust 2024 stabilization.

Tracking for broader RFC 3627 work:

• Tracking Issue for match ergonomics 2024 (RFC 3627) #123076