Implement `Clone` for generators

[canndrew]

Proposal

It would be nice if generators, like closures, could automatically implement Clone and Copy where possible. Is this something that the lang team would consider desirable? (It would certainly be useful to me).

There is some prior discussion of this on zulip here: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/.60Clone.60.20for.20generators

Mentors or Reviewers

@tmandry? @estebank?

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[canndrew]

I have implemented this here: https://github.com/canndrew/rust/tree/clone-generators

Would someone be willing to review it?

[oli-obk]

@rustbot second

[nikomatsakis]

@rustbot label +I-lang-nominated

Let's discuss this briefly in the lang meeting, but it seems good to me. The idea is to make generators implement Clone/Copy if they can, just as closures do now.

[nikomatsakis]

We discussed this in today's @rust-lang/lang meeting and the general consensus was that we were in favor of this change and that no RFC was required (this can be considered a logical extension of rust-lang/rfcs#2132. It would still require a tracking issue and an FCP on the PR that implements it -- it would also be good, @canndrew, to do a write-up of the proposed design for that issue (presumably a small one) to help guide the stabilization report.

[canndrew]

Sorry for the delayed response. I've been busy with work/life.

I've updated the PR to pass the CI checks and I've opened a tracking issue which includes a short write-up of the feature. Is this write-up the sort of thing you had in mind?

[apiraino]

@rustbot label -final-comment-period +major-change-accepted