Tracking Issue for match ergonomics 2024 (RFC 3627)

[Jules-Bertholet]

This is a tracking issue for changes to match ergonomics for the 2024 edition, as described in rust-lang/rfcs#3627.

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

• mut ref/mut ref mut (#![feature(mut_ref)]) Match ergonomics 2024: implement mutable by-reference bindings #123080
  • Bikeshed (ref (mut/ref mut (mut?)
  • Update all pattern diagnostics to ensure they know about this
• Changes to & and &mut patterns (#![feature(ref_pat_eat_one_layer_2024, ref_pat_eat_one_layer_2024_structural)]) Match ergonomics 2024: Implement eat-one-layer #123512
• Allow & patterns to consume &mut references Match ergonomics 2024: let & patterns eat &mut #124567
• Don't reset binding mode on mut with edition >= 2024 Match ergonomics 2024: mut doesn't reset binding mode #123535
  • Edition migration lint (without rustfix)
• Rustfix Match ergonomics 2024: migration lint #124639
• RFC Match ergonomics 2024 rfcs#3627
  • Original design doc: https://hackmd.io/YLKslGwpQOeAyGBayO9mdw.
• N/A: Add documentation to the dev guide.
  • See the instructions.
• Stabilize Rule 1C, Rule 2C for Rust 2024.
  • Implement edition 2024 match ergonomics restrictions #131381
• Stabilize Rules 3-5 for all editions.
• Add documentation to the reference.
  • See the instructions.
• Add documentation to the edition guide.
• Ensure ready for Rust 2024 stabilization.

Tracking for Rust 2024 changes:

• Tracking issue for Rust 2024: Match ergonomics rules 1C/2C #131414

Unresolved Questions

• mut ref mut vs ref mut (mut syntax
• The HackMD says the reference types should be "compatible", what does this mean and why?

### Implementation history
- [ ] https://github.com/rust-lang/rust/pull/122978
- [ ] https://github.com/rust-lang/rust/pull/123080
- [ ] https://github.com/rust-lang/rust/pull/123311
- [ ] https://github.com/rust-lang/rust/pull/123512
- [ ] https://github.com/rust-lang/rust/pull/123535
- [ ] https://github.com/rust-lang/rust/pull/124047
- [ ] https://github.com/rust-lang/rust/pull/124567
- [ ] https://github.com/rust-lang/rust/pull/124639
- [ ] https://github.com/rust-lang/rfcs/pull/3627
- [ ] https://github.com/rust-lang/rust/issues/125058
- [ ] https://github.com/rust-lang/rust/pull/125084
- [ ] https://github.com/rust-lang/rust/pull/125168
- [ ] https://github.com/rust-lang/rust/pull/127008
- [ ] https://github.com/rust-lang/rust/issues/127257
- [ ] https://github.com/rust-lang/rust/pull/127369
- [ ] https://github.com/rust-lang/rust/issues/127559
- [ ] https://github.com/rust-lang/rust/pull/135237

See also #105647, #64586

@rustbot label T-lang A-patterns A-edition-2024

[Nadrieril]

Noting here that I no longer think we need the "&<pat> everywhere" part of the proposal. This makes the proposed fix less local but saves us in design and possible conflicts with deref patterns.

[Jules-Bertholet]

possible conflicts with deref patterns.

Can you elaborate? edit: oh I see, https://hackmd.io/YLKslGwpQOeAyGBayO9mdw#Deref-patterns

[traviscross]

@rustbot labels +I-lang-nominated

@Jules-Bertholet has picked up this work and is looking for a liaison for the experiment. Let's nominate to discuss.

[traviscross]

@rustbot labels -I-lang-nominated

We discussed this is in the lang meeting today, and I'll be picking up liaisoning on this one. Please let me know whenever anything is needed to move this forward.

Thanks to @Nadrieril for the original work here, and thanks to @Jules-Bertholet for carrying the torch forward.