Tracking issue for way to express intraprocedural finite state machines

[traviscross]

This is a tracking issue for some form of:

• RFC: Improved State Machine Codegen rfcs#3720

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

From #138777:

This feature is based on rust-lang/rfcs#3720, though it does not exactly implement it. Rather, this is a language experiment to figure out how to impove that RFC. So, the RFC will eventually match the implementation we end up with, rather than the other way around.

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

• Approve as lang experiment.
  • Add #[loop_match] for improved DFA codegen #138780 (comment)
• Accept an RFC.
  • RFC: Improved State Machine Codegen rfcs#3720
• Implement in nightly.
  • Add #[loop_match] for improved DFA codegen #138780
• Add documentation to the dev guide.
  • See the instructions.
• Add documentation to the reference.
  • See the instructions.
• Add formatting for new syntax to the style guide.
  • See the nightly style procedure.
• Stabilize.
  • See the instructions.

Unresolved Questions

TODO.

Related

TODO.

cc @bjorn3 @folkertdev @rust-lang/lang

[scottmcm]

I object under the phrasing as labelled matches. See rust-lang/rfcs#3720 (comment)

(I'm puzzled why an RFC open for less than a day got a tracking issue and label, TBH.)

[traviscross]

Some form of this seemed particularly likely to me to yield a request for an experiment, especially as they already have implementation work, so the tracking issue was for a place to hang that.