Use zcash_script’s new Script trait

[sellout]

Motivation

This is a precursor to testing the Rust implementation of Zcash Script.

Blocked-On: ZcashFoundation/zcash_script#171 and publishing a new version of zcash_script with those changes.

Solution

This uses a trait that wraps the C++ Zcash Script implementation. As we progress toward cutting over to a Rust implementation, this trait will additionally have impls for the Rust version and a variant that runs both C++ & Rust, comparing the results.

Additionally, this eliminates a few cases from zebra_script::Error that can never be produced.

Tests

The tests are the same as the previous zebra_script tests – there should be no change in behavior.

Follow-up Work

This is blocked on a release of zcash_script containing ZcashFoundation/zcash_script#171.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.

[sellout]

This depends on ZcashFoundation/zcash_script#171.

[mpguerra]

Thank you for your PR! We're focusing on changes for NU6 testnet activation at the moment so we won't be able to prioritise this review for another week or two.

[sellout]

Re: the unchecked checkboxes

• there are no visible changes to add to the CHANGELOG and
• I don’t have permissions to add labels.

[arya2]

Re: the unchecked checkboxes

• there are no visible changes to add to the CHANGELOG and

We usually check boxes if they don't apply to the PR.

• I don’t have permissions to add labels.

Added a priority label.

Added a do-not-merge label as well, we should wait until the changes in zcash_script have been published before merging this PR.

[mpguerra]

Added a do-not-merge label as well, we should wait until the changes in zcash_script have been published before merging this PR.

What's next here? I see ZcashFoundation/zcash_script#171 has merged

[conradoplg]

What's next here? I see ZcashFoundation/zcash_script#171 has merged

We should double check this PR works with zcash_script main branch, and then I can make a zcash_script release and we point to that instead.

[sellout]

We should double check this PR works with zcash_script main branch, and then I can make a zcash_script release and we point to that instead.

I can do this, but wondering how to show that it’s successful – should I put up a temporary PR that just fetches zcash_script from GH instead of the crate registry and shows that everything still passes? And we’ll just close it afterward?

Also, I’m happy for there to be a zcash_script release now, but I figured it would be fine to leave it until the next PR or two land on zcash_script, which contain the actual Rust implementation.

[sellout]

You can simply change Cargo.toml in this PR to point zcash_script to a specific commit in its repo (i.e. the one corresponding to its current main), which I think would also make CI pass here.

Ok, this now points at the zcash_script master branch. I also made a PR (#8896, to be discarded) that shows that the current Zebra main branch (without this PR) will also work with the new zcash_script.

[mpguerra]

What's next here? I see ZcashFoundation/zcash_script#171 has merged

We should double check this PR works with zcash_script main branch, and then I can make a zcash_script release and we point to that instead.

I guess @sellout has done this already in #8896?

@conradoplg shall we do the zcash_script release and merge this?

[sellout]

I should have ZcashFoundation/zcash_script#175 merged today, which is effectively an addendum to ZcashFoundation/zcash_script#171, so it’s probably worth getting that in before the release … and I think it will involve at least a small change to this PR as a consequence.

[conradoplg]

I went ahead and updated this for the latest zcash_script which should be now working.

CI should fail only the cargo deny sources check since it's pointing to zcash_script master branch.

[sellout]

I wonder if the ZcashScript instance that’s used should be handled by a feature flag? I intended the CxxRustComparisonInterpreter to be mostly for testing, expecting one or the other to be in the release.

[conradoplg]

I wonder if the ZcashScript instance that’s used should be handled by a feature flag? I intended the CxxRustComparisonInterpreter to be mostly for testing, expecting one or the other to be in the release.

A feature flag sounds good. I seem to recall that the plan was to run both together for a while until we have assurance that the Rust one is equivalent, and then switch to the Rust one and get rid of the C++ one.

[nuttycom]

I wonder if the ZcashScript instance that’s used should be handled by a feature flag? I intended the CxxRustComparisonInterpreter to be mostly for testing, expecting one or the other to be in the release.

A feature flag sounds good. I seem to recall that the plan was to run both together for a while until we have assurance that the Rust one is equivalent, and then switch to the Rust one and get rid of the C++ one.

Yeah, I think it's important for some nodes to be running both simultaneously, taking the results from the C++ interpreter but loudly announcing any divergences. Probably even halting if there's a divergence, so that the node is left in a state where it's debuggable.