Add Clone support for ProofWithPublicInputsTarget

[tikhono]

When I have done some recursive example, I found out the lack for Clone derive for ProofWithPublicInputsTarget.

Here example: https://gist.github.com/tikhono/6b3222ccaa2030280efcbc7038eeb373

Does the usage of clone correct? Or lack of this derive is intendant, so there are some reasonings for this?

[dlubarov]

Thanks for sending, this sees fine to me if it's needed. That said I think there are a couple other potential fixes,

• It looks like our current recursion examples call set_proof_with_pis_target before verify_proof. It does seem a bit odd to require that ordering though.
• We could change verify_proof to make proof_with_pis a reference. I think we usually take references to "target" structs (besides small ones which impl Copy); AFAIK there wasn't a particular reason we took a value in this case.

Do you think the reference change would address the issue for you?

[tikhono]

Yes, I think reference should work for me.

Thanks for fast response!

[dlubarov]

Sounds good! I made #828 to change that, it might just be a bit delayed as our build is broken at the moment (rust-lang/rust#105037)