[R-pkg-devel] Feedback on "Using Rust in CRAN packages"

[Simon Urbanek]

> On 13/07/2023, at 2:50 PM, Kevin Ushey <kevinushey using gmail.com> wrote:
> 
> Package authors could use 'cargo vendor' to include Rust crate sources directly in their source R packages. Would that be acceptable?
> 


Yes, that is exactly what was suggested in the original thread.

Cheers,
Simon



> Presumedly, the vendored sources would be built using the versions specified in an accompanying Cargo.lock as well.
> 
> https://doc.rust-lang.org/cargo/commands/cargo-vendor.html
> 
> 
> On Wed, Jul 12, 2023, 7:35 PM Simon Urbanek <simon.urbanek using r-project.org> wrote:
> Yutani,
> 
> I'm not quite sure your reading fully matches the intent of the policy. Cargo.lock is not sufficient, it is expected that the package will provide *all* the sources, it is not expected to use cargo to resolve them from random (possibly inaccessible) places. So the package author is expected to either include the sources in the package *or* (if prohibitive due to extreme size) have a release tar ball available at a fixed, secure, reliable location (I was recommending Zenodo.org for that reason - GitHub is neither fixed nor reliable by definition).
> 
> Based on that, I'm not sure I fully understand the scope of your proposal for improvement. Carlo.lock is certainly the first step that the package author should take in creating the distribution tar ball so you can fix the versions, but it is not sufficient as the next step involves collecting the related sources. We don't want R users to be involved in that can of worms (especially since the lock file itself provides no guarantees of accessibility of the components and we don't want to have to manually inspect it), the package should be ready to be used which is why it has to do that step first. Does that explain the intent better? (In general, the downloading at install time is actually a problem, because it's not uncommon to use R in environments that have no Internet access, but the download is a concession for extreme cases where the tar balls may be too big to make it part of the package, but it's yet another can of worms...).
> 
> Cheers,
> Simon
> 
> 
> 
> > On 13/07/2023, at 12:37 PM, Hiroaki Yutani <yutani.ini using gmail.com> wrote:
> > 
> > Hi,
> > 
> > I'm glad to see CRAN now has its official policy about Rust [1]!
> > It seems it probably needs some feedback from those who are familiar with
> > the Rust workflow. I'm not an expert, but let me leave some quick feedback.
> > This email is sent to the R-package-devel mailing list as well as to cran@~
> > so that we can publicly discuss.
> > 
> > It seems most of the concern is about how to make the build deterministic.
> > In this regard, the policy should encourage including "Cargo.lock" file
> > [2]. Cargo.lock is created on the first compile, and the resolved versions
> > of dependencies are recorded. As long as this file exists, the dependency
> > versions are locked to the ones in this file, except when the package
> > author explicitly updates the versions.
> > 
> > Cargo.lock also records the SHA256 checksums of the crates if they are from
> > crates.io, Rust's official crate registry. If the checksums don't match,
> > the build will fail with the following message:
> > 
> >    error: checksum for `foo v0.1.2` changed between lock files
> > 
> >    this could be indicative of a few possible errors:
> > 
> >        * the lock file is corrupt
> >        * a replacement source in use (e.g., a mirror) returned a different
> > checksum
> >        * the source itself may be corrupt in one way or another
> > 
> >    unable to verify that `foo v0.1.2` is the same as when the lockfile was
> > generated
> > 
> > For dependencies from Git repositories, Cargo.lock records the commit
> > hashes. So, the version of the source code (not the version of the crate)
> > is uniquely determined. That said, unlike cargo.io, it's possible that the
> > commit or the Git repository itself has disappeared at the time of
> > building, which makes the build fail. So, it might be reasonable the CRAN
> > policy prohibits the use of Git dependency unless the source code is
> > bundled. I have no strong opinion here.
> > 
> > Accordingly, I believe this sentence
> > 
> >> In practice maintainers have found it nigh-impossible to meet these
> > conditions whilst downloading as they have too little control.
> > 
> > is not quite true. More specifically, these things
> > 
> >> The standard way to download a Rust ‘crate’ is by its version number, and
> > these have been changed without changing their number.
> >> Downloading a ‘crate’ normally entails downloading its dependencies, and
> > that is done without fixing their version numbers
> > 
> > won't happen if the R package does include Cargo.lock because
> > 
> > - if the crate is from crates.io, "the version can never be overwritten,
> > and the code cannot be deleted" there [3]
> > - if the crate is from a Git repository, the commit hash is unique in its
> > nature. The version of the crate might be the same between commits, but a
> > git dependency is specified by the commit hash, not the version of the
> > crate.
> > 
> > I'm keen to know what problems the CRAN maintainers have experienced that
> > Cargo.lock cannot solve. I hope we can help somehow to improve the policy.
> > 
> > Best,
> > Yutani
> > 
> > [1]: https://cran.r-project.org/web/packages/using_rust.html
> > [2]: https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
> > [3]: https://doc.rust-lang.org/cargo/reference/publishing.html
> > 
> >       [[alternative HTML version deleted]]
> > 
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