There are breaking changes between v0.11 and v0.12. We have information about the updates required to migrate your code in the Breaking Changes section of the v0.12.0 release notes, and we recommend starting there when migrating. This document will focus on come errors when migrating and their solutions.
Q: I’ve updated my risc0-build package to a known good version and am seeing the following error:
error: no matching package named `risc0-build` found
What’s going on?
A: If you’re encountering a build error with risc0-build, it’s possible that you need to update your rust-toolchain to a new version of rust nightly. An example line follows:
channel = "nightly-2022-10-28"
Q: How do I fix the error “found duplicate lang item panic_impl" (or oom)?
A: This happens if you use Rust Standard Library code in the zkVM guest without telling Cargo you need std support for the guest. If you are using std code in the guest, include "std" as one of the features of risc0_zkvm in the Cargo file for the guest code. (In the directory structure as our Rust starter template, this file is methods/guest/Cargo.toml.) You do still need to disable the default features of risc0_zkvm when it’s a guest dependency (since those include host-side features incompatible with the guest), so the line in the Cargo file will look something like this:
risc0-zkvm = { version = "0.12", default-features = false, features = [ "std" ] }Q: When building the guest methods crate, I’m getting a link error like this:
cannot find function `link` in crate `risc0_build`
What should I do?
A: For version 0.12, the risc0_build::link function is no longer necessary and was removed. Delete any [build.rs](http://build.rs) files that call this function as they aren't needed in this version.
Q: When I update I get an error “failed to select a version for bytemuck" (or some other package), but the details about the error don’t show a conflict. What’s wrong?
A: We believe this is related to yanked crate versions. You need to update your Cargo .lock files for both the host and guest side. If you are using the same directory structure as our Rust starter template, you can do this by running cargo update in both the root directory and methods/guest.